the guitar amplifier player_s guide - dave zimmerman

Table of Contents

IntroductionHow to Use This Book

Part One—Good Stuff

Chapter One—A Good AmpChoosing an Amp

All the Wrong Reasons

Chapter Two—Good ToneTry Recording Yourself

Playing Alone vs. Playing with a Band

Midrange Boost

Good Clean Tones

Clean and Clipping

Good Dirty Tones

A Word About Hum

Power Supply Hum

Heater Supply Hum

Other Forms of Internal Hum

High Gain Hiss

Chapter Three—Benchmark AmpsOlder Fender Tweeds

Later Fender Tweeds

Blackface Fender

Non-Master Volume 100 and 50 Watt Marshalls

Late ’60s to early ’70s

Heads and Cabs

Vox AC30

Dumble and Early Mesa/Boogie

Trainwreck

Master Volume Marshall

High Gain Multi-Channel Amps

Digital or Modeling Amplifiers and Computer Programs

Chapter Four—Great RecommendationsPeavey Classic 30 and Classic 50

Peavey Transistor Amps

Fender Reissue Tweed and Blackface Amps

Marshall 50 Watt Small Box Non-Master Volume Head

Marshall JCM800

Vox AC30

Two Rock

Tone King

Matchless

Trainwreck

Speaking of Decent Folks

Part Two—Tweaking Your Tone

Chapter Five—Dowsing for ToneReplacing a Speaker

Connecting Speakers — Series and Parallel

Removing Power Tubes

Biasing the New Power Tubes

Changing Rectifier Tubes

Tube Rectifier

Magic Resistor

Chapter Six—Cultivating Your StylePlaying a Non-Master Volume Amp

Jumping Channels in Vintage or Reissue Amps

Playing a Master Volume Amp

Chapter Seven—SpeakersFrequency Response

Efficiency

Power Handling Capability

Anatomy of a Guitar Speaker

Magnet Material

NIBs

Speaker Cone Material

Wood Fiber

Aluminum Cones

Hemp Cones

Speaker Diameter

Eight Inchers

Ten Inchers

Twelve Inchers

Fifteen Inchers

Speaker Manufacturers

Celestion

Jensen

Eminence

Ohms

Resistance and Impedance

Ohms, Practically Speaking

Chapter Eight—CabinetsOpen vs. Closed-Back Cabinets

Getting the Most Bass from Your Cab

Speaker Cloth

Chapter Nine—Power TubesOctal Power Tubes

EL84s

Power Tube Life

Tube Manufacturers

TAD, Ruby Tubes and Groove Tubes

JJ-Electronic

Svetlana

New Sensor

Tube Rectifiers

Chapter Ten—Preamp TubesNOS Preamp Tubes

Chapter Eleven—Cords and CablesGuitar Cable

Capacitors and Capacitance

Harmonic Content of a Sound Wave

Time Domain of a Sound Wave

Electronic Buffer

Speaker Cables

Ribbon Speaker Cable

Power Cable

One Last Tip

Chapter Twelve—A Word About VolumeWhy Higher Volume Sounds Better

Amp Response At Higher Volumes

Human Ear Response to Higher Volume

Wattage Knobs

Dummy Loads (aka Attenuators)

Master Volumes

Variable Transformers (aka Variacs)

The Sag Circuit

Part Three—The Basics

Chapter Thirteen—Amplifier BasicsThe Preamp

Gain Control

EQ/Tone Controls

Effects Control

Reverb

Tremolo/Vibrato

Effects Loops

The Power Amp

The Phase Inverter

Presence Control

Transformers

Choke or Inductor

Transformer Basics

Speakers and the Power Amplifier

Line Out

Chapter Fourteen—Distortion BasicsGain

Distortion

Clipping Hard and Soft

Harmonics

Harmonics and Clipping

Sub-Harmonics

That Ringing Fuzz Sound

Attenuators and Dummy Loads

Opportunities for Distortion

Overdrive and Boost/Distortion and Fuzz

Overdrive and Boost

Distortion and Fuzz

Preamp vs. Power Amp Distortion

Preamp Distortion

Power Amp Distortion

Power Supply Sag

Speaker Distortion

Chapter Fifteen—Tube BasicsTube Strengths

Transistor Strengths

How Tubes Work

Grid Voltage

Diodes

Rectifier Tubes

Triodes

Tetrodes

Pentodes

Kinkless Tetrodes

What’s in a Name?

Chapter Sixteen—Safety BasicsA Word About Attenuators

Speakers, Loads and Speaker Cable

Chapter Seventeen—Equipment Grounding The Death Switch

The Ground Wire

Part Four—Appendices

Appendix A—Speaker Ohm Charts 30 Watt Amplifier

50 Watt Amplifier

100 Watt Amplifier

100 Watt Amplifier

Appendix B—Power Tubal TonesTube Tone Characteristics

Tube Substitution Chart

Appendix C—Preamp Tube TypesPreamp Tube Types

Appendix D—Amplifier Block Diagrams

Checklists and Glossaries

Checklist A—Choosing an AmpPersonal Considerations

Amp Specific Questions

Checklist B—Safety GuidelinesSafety Guidelines Playing Your Amp

Safety Guidelines Working on Your Amp

Glossary A—Technical

Glossary B—Tonal

About the Author

theGUITARAMPLIFIERPLAYER’S GUIDEAn instruction & reference manual for musicians 2nd edition

Dave Zimmerman

Green Frog Publishing • East Montpelier, VT

The Guitar Amplifier Player’s Guideby Dave Zimmerman

Copyright © 2010 Green Frog Publishing.

Green Frog PublishingP.O. Box 46East Montpelier, VT 05651greenfrogpublishing.com

Second EditionWritten by Dave ZimmermanEdited by Cecilia BizzocoCopy edited by Jeff HoerthCover design by Nancy Sepe of Star Hill Studio DesignCover portrait by Lynn Bohannon of Lynn Bohannon Photography

All rights reserved. No part of this book may be reproduced or copied in any form or by any means, or stored in any database or retrieval system whatsoever without written permission from the author, except for brief quotations in articles or reviews where the source is made clear. For information, contact Maven Peal Instruments.

Green Frog Publishing is a trademark of Green Frog Publishing, and is not associated with any amplifier company or performing artist. All product and artist names and services identified throughout this book are used in editorial fashion only and for the benefit of such companies and artists with no intention of infringement of trademark. No such use, or the use of any trade name, is intended to convey endorsement of or other affiliation with this book.

Never remove your amplifier from the chassis without a technician’s assistance. Please refer to “Chapter Sixteen—Safety Basics” for more information. The information contained in this book is on an “As Is” basis without warranty. While every precaution has been taken in the preparation of this book, neither the author nor Maven Peal Instruments shall have any liability to any person or entity with respect to loss or damage caused or alleged to be caused directly or indirectly by the instructions contained in this book or by the musical equipment described in it.

EAN-13 978-0-9914359-4-4

Printed and bound in the United States of America.

http://www.greenfrogpublishing.com

http://www.starhilldesignstudio.com

http://www.lynnbohannonphotography.com

http://www.mavenpeal.com

Dedicated to Alexander.

Special thanks to Jeff Chapman, Ed & Deb Miller, Tom Wurtz and Al Walker.

... because it makes me feel good.

I was fascinated by music as a child. Playing my guitar takes me back to the wonderment I felt when I was young. When I hit a chord or play passage just right it makes me happy. I feel like I’m connected to a greater consciousness and all the great players that came before me... I can’t really explain it... the music was there before me, it will be there long after I’m gone... when I play, it makes me feel like all is right...

Joe Columna

Introduction

What I’ve found most surprising over the past twenty years making boutique amplifiers is the confusion — I suppose my marketing colleagues would consider it the “mystique” — surrounding what makes a great amplifier great.

While it is no secret that tubes and power amp distortion are a large part of what is behind the mystique, I imagine that larger manufacturers would be thrilled if guitarists would forget about tubes and power amp distortion. Tubes are just too expensive to make and too fragile to distribute. Eloquent power supplies and power amps are far more expensive to engineer and manufacture than transistor power supplies and power amps.

To make matters worse, much of the information available about amps, whether online, from stores or in books and magazines, is less than objective due to chasing the almighty dollar. The rest is esoteric, and for most, difficult to understand.

So, many players resort to buying the amp their favorite artist plays.

Once upon a time, big amp makers would give big name artists free amplifiers, and artists would actually play them.

Sadly, now manufacturers pay artists to use, or at least say they use, their amps. When a manufacturer makes a special artist model that “was designed in conjunction with guitar hero Sam Smith,” every one of those amps that manufacturer sells puts money into Sam Smith’s pocket.

And rightly so, you might add. Except the amps Sam Smith is using on stage an amp that has most likely been modified from the off-the-shelf model available to you in the store.

It gets worse. There have been instances when the Sam Smith model on stage has a light on, maybe even some tubes glowing, but Sam is actually plugged into a completely different, modified, vintage or boutique amp deftly hidden from the audience.

Another aspect that adds to the confusion surrounding what makes a great amp great is that artists like to keep their recording methods secret. The classic example is Jimmy Page of Led Zeppelin.

You can see the live concerts of Page in front of 100 or 200 Watt Marshall stacks. In the studio, however, Jimmy favored little amps and kept quite secret about what he was using. The speculation I hear most is that he used Supro amps, which makes sense listening to the raspy, bluesy tone on the first two Zeppelin albums.

So as a musician, you have many obstacles in your path as you try to figure out what works and doesn’t work for you.

The goals of This book are To:• Help shed light on the subject of guitar amp tone for both novice and pros.

• Help you understand the terms everyone uses when talking tone.

• Help you make tonal tweaks to your setup yourself before taking your amp to a tech to be modified, or bagging it altogether for a new one .

When I make suggestions for products that I like and why, keep in mind that I generally favor more vintage-style rock guitar sounds like earlier Van Halen, Led Zeppelin, The Rolling Stones, The Black Crows, Tool, The Red Hot Chili Peppers, ZZ Top, AC/DC (especially with Bon Scott), Alex Lifeson (who has a huge variety of tones), Jeff Beck, Sonny Landreth (the best slide player ever and an extremely nice person), Jimi Hendrix and of course the king of tone, Eric Johnson.

I also like a lot of bluesy stuff like B.B. King, Albert King, Stevie Ray Vaughn, Buddy Guy, Muddy Waters, Son House, etc. Some of the early rock and roll, while not my style, has tremendous guitar playing with great tone. Check out Elvis Presley and listen to the guitar.

I also like a lot of the more contemporary hard rock bands like The White Stripes, Jet, Three Doors Down, Staind, Seether, Lamb of God, and of course, Tenacious D.

I’m not the biggest fan of metal; some of it I do like, but much of it needs to have the bees removed before it really engages me. With the right equipment and approach, great metal tone can be had without the can-full-of-bees syndrome. For me, being able to tell what chord you are playing is important. When the tone gets so over-the-top distorted that you can play C or C# and nobody knows the difference, I’m a little put off.

That said, nothing sounds as great as an amp that seems as if it is about to blow up à la Neil Young or Jack White.

While I don’t personally listen to a lot of country or jazz, everyone can learn a thing or two about the clean-to-moderately distorted tones of great guitarists from these genres. One of the hardest goals to accomplish as an amp designer is to make great clean tones, so I really respect them when I hear them.

When playing clean, you can’t hide behind a lot of distortion or sustain. You really have to work your rig to get what you want out of it. As a result, jazz and country players tend to have really amazing technique. Nothing is more intimidating than sitting in with a guy who shows up to the gig with a vintage amp, a cord and his Tele.

So even if you are a dyed-in-the-wool metal head, spend a little time listening to a few tamer styles to get some tonal and technical ideas.

How to Use This Book“Part Two—Tweaking Your Tone” is the heart of this book. If you already know what tone you’re after (“Part One—Good Stuff”), and you already know how your amp works — or don’t honestly care — (“Part Three—The Basics”), then you only need to read “Part Two—Tweaking Your Tone”. This section is full of practical tips and instructions for customizing your amp’s tone. Before reading “Part Two—Tweaking Your Tone” please take a moment to review “Chapter Sixteen—Safety Basics”

“Part One—Good Stuff”You’ll find instructions to help you define the tone you seek.

“Part Two—Tweaking Your Tone”An overview of the various tonal tweaks you can make by yourself or with your tech. Includes step-by-step instructions for modifying your amp’s setup. Please take a moment to review “Chapter Sixteen—Safety Basics”before making any changes to your amplifier.

“Part Three—The Basics”No instructions here! “Part Three—The Basics” is chock-full of easy to read information on the technical background behind how your amp works.

“Part Four—Appendices”• “Checklist A—Choosing an Amp” contains six charts detailing the correct Ohms to use when hooking

up two speakers.

• “Appendix B—Power Tubal Tones”contains two charts showing the tonal characteristics and correct substitutions for different types of power tubes

• “Appendix C—Preamp Tube Types”contains two charts detailing different types of preamp tubes.

• “Appendix D—Amplifier Block Diagrams” contains two amplifier block diagrams; one of a vintage amp, the other of a typical modern amp.

To help organize your search for the perfect amp/tone, the “Checklist A—Choosing an Amp” checklists take into account your personal preferences as well as an amp’s individual characteristics. The “Checklist B—Safety Guidelines” checklists are essential when playing and working on your amp.

You’ll find “Glossary A—Technical” and “Glossary B—Tonal” describing terms everyone throws around but might not always understand.

Amplifiers carry high voltages; this translates to a lot of heat and volume. Throughout the book, I use three symbols to call your attention to possible dangers that you need to be aware of.

0 WARNINGFollow these instructions to avoid blowing your amp, getting yourself electrocuted or starting a fire.

� WARNINGFollow these instructions to avoid hearing loss or tinnitus.

Ω WARNINGFollow these instructions to avoid damage to your speaker(s).

Finally, the quotes at the beginning of each chapter are from customers and players I’ve had the pleasure of knowing over the years. I asked them why they love playing their guitar.

Regardless of the style of music you play or how experienced you are, I hope this book clears some of the mystery surrounding guitar amps and helps you discover the tone that inspires you to become the best musician you can be.

Enjoy!

Part One—Good Stuff

01 | “Chapter One—a GOOd amp”

02 | “Chapter twO—GOOd tOne”

03 | “Chapter three—BenChmark amps”

04 | “Chapter FOur—Great reCOmmendatiOns”

There is always music playing in my head. It might be anything from a nursery rhyme to Thelonious Monk and it will only subside if I pick up a guitar and play. I don’t know if it’s love anymore, I MUST play my guitar!

Spencer Ross

Chapter One—A Good Amp

A $3,000 amp with a $300 guitar always sounds better than a $300 amplifier with a $3,000 guitar. This concept is difficult for most players to digest, because after all, you are playing the guitar. But it’s true. So if your funds are limited, investing in a good guitar amp will have more positive impact on your tone than investing the entire budget on a great guitar.

A good guitar amp is as interactive and responsive (if not more so) as a great guitar. If your amp makes the same sound regardless of how you play the strings, you have a virtual keyboard, not a guitar amplifier.

Before I get into the details of what a good amp is, allow me to put all my personal prejudices on the table. I feel that transistor amps are best left to beginners who simply can’t afford a tube amp. While I have heard masters like B.B. King create wonderful tone from a Gibson Lab Series transistor amp — I can’t. I am just not good enough and you probably aren’t either. That said, I have played one or two fairly engaging transistor amps that are fun and, of course, lightweight and virtually maintenance free.

Ditto for digital modeling/computer amps. Every time I get a hold of a modeling amp, I feel as though it sounds and responds as if I’m playing through a robotic simulation of reality and I just want Out-of-The-Matrix. However, if you can’t afford a real guitar amp, plugging into something like GarageBand can be an excellent substitute and a great learning tool.

I am partial to high-end (boutique or vintage) tube amps. These amps offer an organic quality and engagement that doesn’t exist in most mass-produced tube amps. However, you may be surprised at how many inexpensive amps have a lot of the characteristics you are seeking when buying an amp.

Choosing an AmpWhat are those characteristics? While some are desirable to all players, others will depend on your specific needs.

When considering an amp, ask yourself These personal quesTions: • Do I need this amp for a wide variety of tones, or can I afford to get different amps for different tones?

If you are looking for a particular sound and don’t really care if your amp can do anything but that one sound, you just made your search much easier.

• Am I going to gig with this amp? If so, does the band’s PA allow me to mic my amp?

If you are going to gig with the amp, or can’t afford a collection of amps just yet (or roadies to lug them around), you most likely won’t want to go with a one trick pony. You will need a more versatile amp.

An amp that offers one great tone, no matter how fantastic that tone may be, usually won’t give you the versatility you’ll need when playing live, especially if you’re playing different rooms. While a more versatile amp might not offer one mind-blowing fabulous tone, the variety of tones it does offer will be more important to you during a gig.

If you can, stick a microphone in front of your smaller amp and let the PA create the volume needed for the audience. Then all your amp has to do is create great tone; it does not need to be really high-powered.

If you can’t mic your amp, you are probably going to need a relatively higher-powered amp to project into the audience — ideally one with a Wattage knob so you can adjust to different-sized rooms.

• How loud is my drummer?

As far as the stage volume is concerned, your amp needs to keep up with, but not overwhelm, your

drummer. If your drummer is really loud or you can’t mic your amp, you will need a high-Wattage amp.

• How loudly can I, or do I want to, play in my normal practice space?

Please be kind to everyone’s ears, including your own. If you can’t or don’t want to play really loudly, get a lower-Wattage amp so you can push the power amp into distortion without blowing your head off.

noW ask yourself These amp-specific quesTions:• Is the amp excessively noisy?

All amps are a bit noisy, but too much is a big negative.

• Does the amp have good string-to-string articulation when played both clean and distorted? Can I hear each individual string or do chords just turn into a roaring mush? Does the amp engage me and make me want to play? The answer to the last question may be in opposition to your answer to the first two questions. An articulate amp will not allow you to hide bad technique nor will it hide a crappy guitar. In fact, a great amp can make you feel initially like your guitar and/or your playing sucks.

Remember, you’ll never improve your playing style with an amp that sounds the same no matter how you play the strings, and you’ll never get great tone from a guitar with bad tone. An articulate amplifier can help you work on both issues.

• Does the amp fart out at the low end when pushed?

Some farting is OK if other aspects of the amp’s tone are just what you’re looking for. Many amps just won’t hold together on the low notes when overdriven. If you’ve got a powerful bass player, you don’t need your low end to be in your face. On the other hand, if you want to take up all of the sonic space you can with your tone, then you will want the bass end to hold up as much as possible.

• Does the amp take pedals well?

Many amps lose their character when playing with pedals. A good amp should be enhanced by pedals, not overwhelmed by them, particularly Boost and Overdrive pedals.

• Does the amp respond to my touch or does it feel like I’m playing a keyboard?

With high-gain settings you will often get the on/off keyboard-like effect. Good high-gain amps will give you the distortion/overdrive you want while remaining responsive to your touch.

• Does the amp sound good with both humbuckers and single coil pickups?

Some amps feel like a spike is being driven into your head when you plug in a Tele, while others sound like mush when you use a Les Paul. Be aware of how your guitar(s) affects your tone. Bring your guitar(s) with you when you try out an amp.

• Does turning the amp’s tone controls actually do something?

I don’t know why, but far too many manufacturers don’t seem to have this point down.

• Is the amp excessively buzzy when distorted?

When you hit a note or chord, can you hear a zing, fizz or buzz riding along the note? If so, you will be fighting that problem a lot if you ever decide to record.

• Are the amp’s power tubes self-biasing/cathode-bias or fixed-bias? If the power tubes are fixed-bias, does the amp offer an external bias feature so I can measure and change the bias current without taking the amp apart?

Power tubes wear out. If your amp isn’t cathode-biased (aka self-biasing) or doesn’t offer an external bias feature, you won’t be able to swap out old tubes without lugging your amp down to your tech. You will either be visiting your tech more often than you’d like, or you will learn to live with worn-out and/or poorly biased power tubes.

Self-biasing amps automatically adjust the bias to your new tubes, while external bias features allow you to easily adjust the bias from the back panel. Being able to adjust the bias opens up a new world of tweaking your amp’s tone, and enables you to keep tabs on your amp’s health.

Believe it or not, some fixed-biased amps exist that offer absolutely no bias adjustment at all, external or internal. The inability to adjust the bias is simply unacceptable, and I would never consider purchasing such an amp unless it were a vintage gem; then I would add a bias adjustment to it.

All the Wrong ReasonsI have noticed over the years a number of self-destructive reasons that seem to factor into some amp buying decisions. If you hear any of the following thoughts floating around in your head, please walk away and try again later.

My friends and/or the people on the news group really like it.

Really, please make your own decisions about what works for you since you are the one who has to play it.

I like the color.

Tolex or stain color are more important to some people than you would ever guess.

I don’t want to wait to buy the amp I really want but can’t afford, so I am going to get this one for now.

Stop right there. You are just encouraging amp manufacturers to make more crap that will eventually end up in a landfill. Please, if you are serious about your guitar, save up to buy the amp that allows you to shine. Then, if you ever move on to a different amp, or decide to stop playing altogether, you will have a much easier time selling a good amp on ebay or The Gear Page than unloading a boat anchor elsewhere.

I saw one in my favorite video on MTV.

Are they even playing videos anymore? If they are, you really cannot tell what the guitar player used to record that song by looking at the video. Think about it for a moment (the advertiser who put that amp in the video hopes you won’t).

Let’s say you are a famous rock star and play a Trainwreck amp, worth around $10k. Are you really going to bring it down to the studio set and let the dancing girls spray shaving cream all over it?

They are having a sale at the guitar store.

The guitar store (like the car dealership) is one of the last bastions where you can still haggle over price. I personally hate doing this, but you can almost always get 10% or more off anytime if you really push it.

The amp has the latest whiz-bang effect built into it.

Please remember that this is a guitar amplifier, not a Bass-O-Matic. If you want effects, get great pedals. A lot of bad amps try to mask bad tone with all kinds of effects. An amp needs to sound good first without any effects.

The amp has 15 thousand Watts, so it must be better than the one that only has 15 Watts.

The truth is, unless you play wicked clean all of the time, or are a real rock star playing large stadiums, you will never need more than 20 or 30 Watts.

It has tubes, so it must be good.

I like tubes too, but I have seen my share of amps that simply have a tube in them for show (that’s right, the tube isn’t connected to the signal path). And many amps with an all-tube signal path still don’t sound so good.

The amp has been modded/made by the genius who mods/makes all of God’s amps.

If the amp doesn’t sound good to YOU, then it doesn’t matter if it sounds good to anyone else. That, ladies and gentlemen, is the bottom line.

Because it puts me in the state of sat-chit-ananda.*

Viphea Mam* Sat means being; Chit means consciousness; Ananda means bliss or rapture; from Joseph Campbell’s book, The Power of Myth,

page 120.

Chapter Two—Good Tone

Good Tone is extremely difficult to describe — nearly impossible as it is to describe Bad Tone. A few common phrases that attempt to describe various tones are loosely defined in ”Glossary B—Tonal”

Some of my favorite good-tone phrases are liquid, crunchy, articulate and punchy. My favorite bad-tone descriptions are harsh, bucket of bees, ice-pick in the forehead/eardrum, and of course the eminently descriptive turn down the suck knob.

With these somewhat less-than-perfect descriptive phrases in mind, talking Tone is a skill developed through experience and interactions with other guitar players. When I say that something “Sounds like a single coil pickup through a vintage Marshall set to crunchy,” these words aren’t going to mean a whole lot to you until you experience listening to several variations on this basic tone.

To get a handle on what Good Tone really means, you need to listen to other guitar players. I am not advocating playing cover songs the rest of your life, but you should broaden your horizons beyond what you normally listen to in the car.

When you find a tone that stands out to you, do research to learn what gear the artist(s) was using (if you can). Death metal players can learn a lot by understanding Eric Johnson’s tone and how he gets those great clean sounds. Blues players can learn something from Joe Satriani and how he uses sustain to play really fluid lines.

Which brings me to a question that all amp manufacturers receive at one point or another: “Will your amp make me sound like Jimmy Page?” I’m sorry, we can’t. Only you can make yourself sound like Jimmy Page... through practice. The right gear will certainly help, but you also need to put some skin in the game.

Artists like Robben Ford, Santana and B.B. King sound pretty much the same no matter what equipment they’re using — proof positive that a very large part of good tone is in your hands. A talented player can wring sustain out of an amp that doesn’t sustain that much, or mellow-out an amp that is too bright simply by changing the pick attack or by finger picking. This reality doesn’t mean a good amp won’t help a mediocre player — it definitely will. What it does mean is that a great player can always overcome a mediocre amp.

For me, the bottom line for Good Tone is whether or not you are engaging your audience. Music is an exchange of energy between musicians and the audience. You have to ask yourself:

Is the audience getting the feeling and emotion that I’m trying to put out there?

This question is sometimes really hard to answer because the tone that gets you going might not have the same effect on your audience. Remember, unless you are fortunate enough to have a legion of fans who want to watch your fabulous technique, the people who are going to see you in the club, download your video and buy your album want to hear SONGS. You need to engage these people and make them want your music.

Try Recording YourselfRecording yourself is a really useful technique to help determine if your tone is coming across like you think it is. You may find that your guitar tone sounds as strange on tape as many people find their own voice to be.

A good example of how your tone is coming across to you versus other people is AC/DC. Many guitarists think that the rhythm guitar (Malcolm Young) is heavily distorted. Consequently, players trying to sound like AC/DC are always going for channel two on their amps.

In reality, Malcolm is just past the edge of distortion into the crunchy area of his amp. (A non-master volume

Marshall will go from clean to crunchy to smoothly distorting as you turn it up more and more.) Malcolm’s guitar also has some particularly gnarly sounding single-coil pickups.

Malcolm’s tone is incredibly engaging, but it is not incredibly distorted. Angus Young has a smoother tone because he has hotter and smoother humbucker pickups in his guitar, has hotter power tubes (EL34 vs. KT66) in his amp, and is turned up louder than Malcolm. Still, Angus is not as distorted or compressed as channel two is on most amps.

Another factor that adds to AC/DC’s tone is when Angus doubles Malcolm’s rhythm — two guitars together sound more distorted than a single guitar.

Many players quickly discover that playing through a really distorted or muddy amp is simply easier than playing through a mildly distorted, crunchy or clean amp. A really distorted amp hides your less-than-perfect playing style in many ways.

Conversely, plugging a single coil guitar straight into a non-master volume amp set to crunchy can give you the feeling of being absolutely naked. You cannot hide, and the audience can hear everything you do.

This high-adrenaline scenario is exactly what makes that tone engaging and really allows you to connect with your audience. When you are really putting yourself out there, your tone is right on, and your playing is in support of the song (not your ego), the experience can be equally inspiring for you and your audience.

A great experiment is to record yourself playing a song alone, and then later with your band.

ask yourself These quesTions abouT your recordings.• Where is your guitar sitting in the mix?

• Are you stepping all over the bass player with your power chords?

• Is your wall of distortion preventing the lead guitar player from cutting through the mix?

• Does your guitar have so much high end (either from your tone control adjustments or high harmonics generated from too much distortion) that you are competing with the singer?

Remember that the amount of distortion perceived by the audience can be very different from the amount of distortion you are perceiving. Quite often, turning the gain up (or volume on a non-master volume amp) doesn’t feel like a bad thing. But in reality, you might be losing dynamics and other nuances that come through with the gain a little lower.

Playing Alone vs. Playing with a BandWhen you’re playing with a band, your guitar doesn’t have to fill as much sonic space as when you’re playing alone. Getting a full sound when you’re alone is easily accomplished by cranking the gain. But when you’re playing with a band, you only need to fill the space the other instruments are not.

While Van Halen’s first couple of albums are among my favorites, they sound like the producers are letting Eddie step all over the entire sound spectrum. So much so that hearing the bass guitar is often difficult.

Of course in the case of Mr. Van Halen, I completely understand why the guitar is showcased. Where the guitar fits in that particular mix was a very conscious decision. You need to be equally conscious of how your tone fits into the mix of your band.

Midrange BoostLike your overall tone, the individual frequencies you need to accentuate when you are playing with your band are different from what sounds good to you when you are playing alone. When you are in a band you want to cut through so the audience can hear you, while not stepping on parts of the spectrum that rightfully belong to other instruments.

For this reason, many guitarists want a midrange boost on their amps. In fact, many pros mod their amps to get increased mid response.

A lot of metal players enjoy the 10-0-10 bass-mid-treble setting (aka the dimebag setting — diming the Bass and Treble and bagging the Mids), finding it easy and fun. But having the ability to boost your mid-range will help you to cut through the band when you need it most.

Good Clean TonesEvery guitarist can work on his or her clean tones.

“Clean” is not the equivalent of plugging your guitar into a stereo, which is what a lot of modern clean tones remind me of.

Metal groups often provide some very good examples of where clean sounds need some work. A lot of metal songs alternate between a clean tone (probably channel one) and a really mid-scooped, highly distorted metal tone (probably channel two or maybe three or four). The clean from channel one is more often than not completely anemic, uninteresting to listen to, and most likely not much fun to play.

Getting a good clean tone is far more difficult than manufacturers would like you to believe.

Clean and ClippingThe two opposite extremes of amp response are absolutely clean and clipping (see ”Chapter Fourteen—Distortion Basics”).

Absolute clean is like plugging your guitar into your stereo or directly into a mixing board — the sound is weak and uninteresting. A good clean tone is when the amp is technically distorting, adding harmonics, not exactly reproducing the guitar signal, but not anywhere near clipping. A good clean sound is full, engaging, balanced and clear.

Absolute clipping is like a fuzz pedal on steroids; the tone is pretty much identical regardless of your technique, guitar, tubes or just about anything else.

The challenge has always been to create a circuit that is imperfect so the note is full, but not specifically designed to clip like a lead channel circuit. Fortunately, the circuits used in vintage amps either fit this bill to a tee or provide a very good starting point.

Good amp tone is responsive to your touch, an expression of your emotions and personality. Getting the clean sound right from the beginning will give you a solid platform to create from.

� WARNINGAlways wear earplugs when playing your amp loudly.

Modern Fat Clean Tones — Experiment OneTry This experimenT:

1. Turn the master volume all the way up using channel one (yes, I know it is going to be loud; put the amp in a closet if you need to).

2. Turn the Gain knob up until the amp is just distorting.

3. Play around with that setting a little bit, cleaning up your tone by turning down your guitar’s Volume knob.

Many amps I’ve encountered will not distort on channel one: Although they sound louder as you turn up the guitar’s Volume knob, they’re still anemic and without character. Other amps just kind of fart out when pushed on channel one, which by the way, is part of the origin of the worst epithet you can say about a tone: It sounds like ass — a great description that allows the mind to contemplate just how bad that sound really is.

Vintage Fat Clean — Experiment TwoFor this experiment, you’ll need a second, lower Wattage one channel amp with a good clean when pushed. A 20 to 30 Watt simple combo amp with a decent 12" speaker and some good tubes is a wonderful platform from which to discover great vintage-type fat clean tones.

for vinTage faT cleans:1. Crank the crap out of the amp (wearing a set of earplugs) and check out how it sounds and feels.

2. Adjust the guitar’s Volume knob to go from clean to crunchy.

3. Switch between your little amp and your metal monster using an A/B/Y box after you have the smaller combo under control and are able to get interesting cleans out of it.

This setup will also allow you to pick the speakers for each amp without attempting to compromise between the two sounds.

Clean and Distorted — Experiment ThreePlaying both a clean amp and a very distorted amp at the same time is also a very cool tone technique — Frampton Comes Alive (double live album, in the ’70s issued to all teenagers with their driver’s licenses) is a classic clean amp plus dirty amp sound.

The clean amp on that album is actually a Roland Jazz Chorus transistor amp — one of the best transistor amps ever made. I believe the dirty amp is a non-master volume 100 Watt Marshall.

Aerosmith started using the multi-amp setup at roughly the same time as Peter Frampton did (mid ’70s) and it works great for both groups. Combining different amp tones can really fill out your sound and be very engaging to the audience.

Good Dirty TonesGood dirty tones can be all over the map, from barely crunchy and in your face to over-the-top screaming with infinite sustain. While it is definitely easier to play an amp with the distortion cranked, that tone may not work with every song.

Being able to get several different dirty sounds out of your setup gives you a healthy variation in tone.

aT a minimum, you should be able To geT The folloWing Tones from your rig:• Barely distorting — a clean tone with some hair on it so that when you play hard the amp barks back

at you, but also backs off when you back off. Blues artists, such as the great Muddy Waters, are great examples of this just barely distorting tone.

• Crunchy — the amp is really breaking up and is in no way smooth. The tone should be really rough around the edges with lots of punch. Think ZZ Top, AC/DC and Jack White’s rhythm tone.

• Singing sustain — you’ve pushed the amp past crunchy to where it is smoothing out and getting a real sweet responsive sustain that cleans up when you back off on your touch. Good examples are Jeff Beck, Eric Johnson and Van Halen’s first couple of albums.

• Distorted screaming — your amp and possibly your pedals are really cooking. Check out Joe Satriani for some serious sustain.

Making a conscious effort to come up with a variety of dirty tones by getting in touch with how your amp responds to different levels of gain will improve your tone and help you become a more expressive and interesting guitarist.

A Word About HumNo, hum is not an organic part of your amp’s tone. Although vintage amps tend to produce a lot of hum, they do not sound great because they hum. Let’s look at where all this hum is coming from.

Power Supply HumWith traditional power supplies, the amount of hum is directly related to how large the filter capacitors are (as measured in microfarads — uF). Larger capacitors hum less. The problem is that the larger the filter cap, the tighter (or less saggy) the amp. So with traditional power supplies, you can’t have both a quiet amp and a saggy amp.

To date, two solutions exist. One is the Maven Peal Sag Circuit, which completely eliminates power supply hum.

The other solution is to increase the size of the filter caps, and then use a tube rectifier to increase sag. The hum won’t entirely disappear, but it won’t be as annoying.

Heater Supply HumVacuum tube heater power supplies are notorious for spraying electrical hum inside an amp. A moderate solution is to have your tech install a hum-nulling circuit to your heater supply.

A more drastic approach would be to have your tech run the tube heaters on DC instead of AC. This approach is effective and is used on preamp tubes of some mass-produced high gain amps. Using DC on both preamp and power amp tubes is rare, but is the most effective method for removing this source of hum.

Other Forms of Internal Hum

Transformers are a source of hum that gets into the electronics if the manufacturer is not careful. You may have experienced this type of hum when you got too close to your amp with your guitar. The pickups will literally “pick up” the transformer hum and happily amplify it for you.

• Other electronic components such as resistors, capacitors, inductors, tubes and transistors generate their own internal noise. Good components generate less noise, but no component is completely quiet.

• If the amp is not made with preamp tube shields, or if the tube shields are not properly grounded (a common problem), hum can enter the tubes directly and then be amplified.

• Transformers in other equipment can also be a problem. For example, if you are too close to a transmission tower, radio waves can cause hum and other types of unwanted noise.

• Fluorescent lights are also a major source of hum.

High Gain Hiss The amount of gain produced by some high gain amps can be well over one million times (see ”Chapter Thirteen—Amplifier Basics”). Even the tiniest bit of noise coming in is amplified until it is clearly audible, and by design these amps offer no way to eliminate all of the noise (due to the high multiplication of signal levels). So if you’re looking for really high gain, prepare to live with some high frequency noise.

In 1965 I was 15 years old and saving up for a drum set. I happened to watch the Yardbirds on T.V. and there was Jeff Beck wielding a Fender Esquire and playing the lead on “Heart Full of Soul.” That was it, I was hooked. I took my money and bought my first guitar. Jeff Beck Still Blows Me Away. I have a Strat and I swear there are notes Jeff gets out of his guitar that are not in mine. Were they an option? The quest to find them drives me still!

Rob Albertuzzi

Chapter Three—Benchmark Amps

Certain amps are used as tonal reference points by musicians to define various tones. Knowing these amps and how they sound will help you better understand what the heck everybody is talking about.

Older Fender TweedsWhile Fender Tweeds were neither the first nor the only amps available during the 1950s, they did very much define early rock ‘n roll and electric blues.

in general, TWeeds:• Are smaller in size (they are all combos).

• Come with a wide variety of speakers (8", 10", 12" and 15" models).

• Use 6V6 or 6L6 output tubes.

• Offer very few features.

• Provide relatively low power and amazingly good tone.

Early Tweeds are fairly easy to push into overdrive with just your guitar. They are rather wild and raspy when on the edge of breakup, yet some are surprisingly smooth when pushed just a bit further.

Fender amps in general — and older Tweed amps in particular — do not offer anything approaching what we would call today a tight bass response. In fact, they can get quite mushy on the bottom end when really overdriven.

This lack of bottom end is a blessing in disguise. If these amps had a lot of bottom, their distorted tone wouldn’t be anywhere as delightful. Instead they would be overly bassy and farty.

I could be wrong because I wasn’t there, but I don’t think any of the above characteristics was originally planned by Mr. Fender (except maybe for the lack of bottom, which is a real Fender characteristic). Yet these amps literally define great tone for the entire industry.

The nasty growl of blues men like Muddy Waters and John Lee Hooker would not have been the same without early Fender Tweeds. Old-school, swampy country music was also greatly influenced by the tone of these amps. Later players would use them when trying to get an authentic bluesy tone, like early Led Zeppelin records and Aerosmith’s first album (a real smorgasbord of vintage amp tones). Tweeds are famously used to get that screaming “about to blow” tone à la Neil Young.

Fender now makes a reissue Tweed Deluxe, and it would be well worth your while to visit a guitar store and get alone in a soundproof amp room with one of these babies. With just a Volume and Tone control, it screams in a really natural, earthy, more-fun-than-humans-are-allowed sort of way.

I’m not saying that the reissues are exactly the same as vintage Tweeds; they most definitely are not — but they are close enough to enjoy.

Later Fender TweedsThe later Fender Tweeds, particularly the 1959 Bassman and Tweed Twin, brought guitar amps to a more refined, punchier, yet still ultimately responsive level. These two amps are so central to the development of guitar amplifiers

that most modern amps can trace their circuitry directly to these classics. Decent reissues of both these amps are now available and worth a try.

The 1959 Bassman was used as the model (I would call it more a direct copy except with British tubes, British speakers and stereo-style transformers) for the first Marshall amps, while later Marshall amps would only be a slight variation on the theme.

In fact, Marshall’s entire success exemplifies the impact that different tubes, transformers and speakers can have on the tone of your amp. More on this later in “Part Two—Tweaking Your Tone”

Later Fender Tweeds have a little more gain to them than earlier Tweeds, so you can push them farther into overdrive, yet they remain smoother and not as wild sounding as their earlier cousins. Later Tweeds feature Bass, Mid, Treble and Presence controls as well as dual, differently-voiced inputs that you can jumper together (you can plug into both inputs at once).

These features all add up to a surprising variety of available tones that are great for everything from country to blues to rock and jazz.

Blackface FenderAfter Tweed amps, Fender created the short-lived brown tolex and white (or blond) tolex amps. Both of these transitional series of amps had unique circuitry that was becoming increasingly complex compared to Tweed amps. The Tremolo circuitry on the blond amps is particularly complex in both circuitry and tone.

In 1964, Fender came out with a new series of amps with new circuitry yet again and began using black tolex and a black front panel (or face). Blackface Fenders have been a classic ever since, and Fender is now reissuing some models.

Blackface Fenders feature Reverb, Tremolo (incorrectly labelled Vibrato) and a significantly updated sound. Compared to Tweeds, Blackfaces are clean, very bright and punchy. Higher-powered models, such as the Twin Reverb, are virtually impossible to break up with just your guitar unless the volume is absolutely deafening — at which point it breaks up with a thick yet bright tone that is still a tad muddy on the bass end, but not in a bad way.

Blackface Fenders are the virtual standard for country, jazz and reggae, yet are also used well in classic rock and the blues. The lower-powered Deluxe Reverb amp sees a lot of use in bands from Ted Nugent to Phish to Creed. The Super Reverb in particular was/is used by Stevie Ray Vaughan and Derek Trucks with great success for its thick, dirty sound.

One of the circuit differences between Blackface and Tweeds was that Blackfaces used a 12AT7 tube for the phase inverter — Tweeds used a 12AX7. The phase inverter circuitry, as well as the 12AT7 phase inverter tube, combine to produce a tighter overdrive than the various phase inverters used in Tweed amps.

While you can try putting a 12AX7 in a Blackface’s phase inverter position, I do not recommend it. The circuitry is really designed for the 12AT7. On a Tweed amp, 12AT7 in this position cleans this amp up.

Later Silverface Fender amps like the Deluxe Reverb are either exactly the same as a Blackface or very close. If you have a Silverface that is not exactly the same as a Blackface (such as the Twin Reverb), your tech can easily turn the circuitry into a Blackface for you.

Non-Master Volume 100 and 50 Watt MarshallsLate ’60s to early ’70sThe first Marshalls were almost exact copies of the 1959 Fender Tweed Bassman circuit, except Marshall used British power tubes (KT66), British Celestion Speakers and stereo-style transformers with significantly extended bass response. Late ’60s and early ’70s Marshalls, known as Plexi amps for their Plexiglas front panel, were variations on the early Marshall theme.

With Plexis, the important changes include using EL34 output tubes, and a couple of tweaks for more mids and more high end. EL34s offer much more gain and a wider (more highs and more lows) frequency response than Fender’s 6L6s. Earlier Marshalls used KT66s, which are closer to the 6L6 tone, but with just a touch of the EL34 character.

Along with more gain, EL34s also offer a much more even frequency response with more lows and more highs than

the mid peaky response of earlier tubes (6L6s and KT66s). The breakup/distortion characteristics of EL34s are also significantly different from the older tubes. EL34s produce a more focused sound that can range from crunchy to creamy depending on how hard you drive them.

Plexi style amps also introduced voicing changes, generally attributed to Jimi Hendrix and his tech, that were incorporated into Marshall’s production amps. The mods included a pronounced increase in the upper mid range, and increased treble boost on the Bright Channel (compared to Fender’s Bright Channel). The center frequency of the Mid control in the Plexi was also changed to be a little higher.

Marshalls amps can have a great clean sound (which is how Stevie Ray Vaughn used his Marshall). But inconsistency in production amps meant you had to really look for one with those great cleans.

Also, depending on which amp you could get a hold of, late ’60s to early ’70s Marshalls could also be very brittle and zingy on the top end. A lot of blame is given to the EL34s, but I really believe it has more to do with the particular parts used to make the amps (which would often change based on what was in stock at the moment). If your vintage Marshall is a little too bright, have your tech take a look to make sure that the correctly valued parts are in there.

Heads and CabsAnother important feature of Marshall amps is their use of separate cabinets for the amplifier (or head) and the speakers. The speaker cabinet features four 12" speakers and is sealed in the back (closed-back) like a stereo cabinet.

This configuration is a stark tonal contrast to Fender, who generally has the amplifier and the speakers housed in a single (open-back) cabinet called a combo. Fender had previously experimented with a closed-back cabinet and a separate head on some of the blond/white tolex amps, most notably the Showman. But combos remain Fender’s mainstay.

Using a closed-back cabinet significantly changed the tone of the amp for Marshall. While open-backed cabinets tend to sound light and airy, filling the space both in front of and behind the speakers, closed-back cabinets are thunderously loud with a tight bass response. The laser-beamy frontal projection (deafening people in the first couple of rows) makes it very difficult, even for players with severe hearing loss, to stay in the same room with a 100 Watt amp playing wide open into one or two 4x12 cabinets. On the other hand, it is also a religious experience — so do it if you have the opportunity and a pair of earplugs.

Marshall originally developed custom speaker cabinets for Pete Townsend, who wanted to project into the audience more effectively. Back in the days of old, little or no help from PA systems could be had, so bands were on their own to create the necessary volume for the hall.

Unfortunately, players got so used to seeing the 100 Watt head with one or more 4x12 cabinets, they mistakenly believed their parents’ basements would be proper venues to let one of these monsters loose. I apologize to any band mates who had to endure the sonic onslaught of their guitar player. I, too, was guilty of this decidedly antisocial behavior (but what fun!).

The Marshall sound, even though based on virtually the same circuitry as a 1959 Fender Bassman, stands alone as one of the most important tonal developments in guitar amplifiers. (And again, as with the Fender Tweeds, manufacturers appear to have been just lucky using the components available at the time.)

Marshall amps for the most part do not mush out when pushed, even when pushed brutally hard. Yet, in the right hands, Marshalls can yield an incredibly creamy “violin” distortion à la Eric Johnson.

Vox AC30The Vox AC30 is the main amp of the Beatles, Tom Petty, Queen and U2. The tone is as unique as its circuitry, tubes and speakers.

The AC30 can be clean with a very pronounced chimey top end. When pushed, this baby can be a thick, but never mushy, rock machine. The AC30 uses EL84s, which are decidedly different from power tubes used in Fenders and Marshalls amps.

EL84s have the most gain of any power tube, a wide, balanced frequency response and a top end that rings like a bell, but doesn’t give you the old ice-pick-in-the-forehead treble that you can get from a Marshall.

The cabinet contains the amp and two 12" speakers in an open back combo configuration. The speakers used are

very old-school Celestion Blues (I believe they were developed in the 1940s), although at times Celestion Silvers were used.

Test driving an AC30 is definitely a worthwhile and fun experience. Make sure the amp has broken-in Celestion Blues or don’t even bother — a new Blue can be really piercing.

Dumble and Early Mesa/BoogieAlexander Dumble of Dumble Amplification and Randall Smith of Mesa/Boogie both seem to have stumbled upon a great way to make an amp really rock (or boogie as it were) somewhere in the late ’60s or early ’70s.

Instead of having to turn up the entire amp to get the overdrive/distortion that players were looking for, these guys added more preamp tubes and put a second volume control between the preamp and the power amp. This design allows players to really distort the preamp while keeping the overall volume low.

Thus, the Master Volume amp was born.

British-made Laney amps, which Black Sabbath uses, offered an extra gain stage via their KLIPP circuit during approximately the same time period. These amps were derived from the 100 Watt Marshalls of the time.

Dumble and Mesa both based their amps on the Fender Blackface. Dumble and Mesa, while similar to a Fender, have a smooth, sustaining tone that Jazz guys have gravitated toward. Carlos Santana has been close with Mesa since the 1970s, and his signature tone is a great example of what these amps sound like when played well. These days, Santana still plays his old Mesa, but he is also rumored to have purchased a couple of new Dumbles.

Mesa went on to become a fairly large amplifier company offering a wide variety of amps, and Dumble went on to building the most expensive amplifiers in the world (somewhere around $35,000 last I heard). The early versions of both these amps sound very similar to me. They have a smooth preamp distortion that is perhaps a little too trebly for my taste.

Dumbles are used by some of the best guitar players in the world, which adds to their reputation for great tone. Interestingly, a large majority of Dumble amps were customized for the musician purchasing them. So I wouldn’t expect two Dumbles to sound alike, which probably adds to their mystique.

TrainwreckIn the early ’80s, Ken Fischer’s company, Trainwreck, took a different approach to offering guitar players more gain/distortion. Ken added more gain to what would normally be found in regular non-master volume amps, but didn’t include a master volume control. Instead, he tuned the amp so that a wonderful mix of preamp and power amp distortion begins as you increase the volume.

Trainwrecks are voiced to be very punchy, in your face and are absolutely my favorite vintage amps. I personally like Trainwrecks that are based around EL84s, which, other than in Voxes, is a power tube that just doesn’t get the attention it deserves.

Master Volume MarshallThe first mainstream, quality tube amps that featured a master volume control were Marshall JCM800s in 1981. These amps not only saved Marshall financially, they became the foundation of the whole 1980s rock and metal sound. Any Hair Metal band worth its salt used a JCM800, often with an overdrive or distortion pedal in front to get a gnarlier lead tone.

On a classic two input Marshall (which has four input jacks), each input is connected to its own gain stage. The gain stages are then added together and sent to the rest of the amp.

On a JCM800, the output of the high gain input stage is connected internally to the input of the low gain input stage — cascading (putting in series) the two gain stages rather than having them run in parallel. The output of the low gain input stage then goes to the rest of the amp, but a master volume control is added after the Tone controls and before the power amp (see “Appendix D—Amplifier Block Diagrams”).

There were some other minor treble-boosting changes, but that is the gist of the amp.

Cascading the gain stages meant that the preamp could be driven deeply into distortion. The master volume control

meant that the signal sent to the power amp could be controlled independently of the gain and the distortion being created in the preamp. Players could then run the power amp very cleanly and get a low volume, preamp distortion which Marshall amps did not previously offer.

Preamp distortion by itself is similar to, yet quite different from, moderate preamp plus power amp distortion. Preamp distortion alone is in some ways similar to the pronounced upper midrange and treble boost created when you use an overdrive pedal to push your amp into power amp distortion. But preamp-only distortion is fuzzier, more compressed and less focused than power amp distortion.

For this reason, if you’re not careful JCM800s also tend to be extremely bright and zingy. Of course, you can still get power amp distortion from a JCM800 by cranking the master volume way up (which is usually how these amps are used in recording studios).

� WARNINGBefore you can successfully emulate Slash’s tone in your basement (which consists of JCM800 preamp AND power amp distortion), you will have to substantially shake the walls. Please wear headphones or earplugs and forewarn the neighbors.

High Gain Multi-Channel AmpsBy the end of the 1980s, two channel amps were fairly common, featuring a clean and a dirty channel. The clean channel generally had two gain stages, while the dirty channel had three.

Think of a stage of gain as the electronics associated with creating a multiplier in the amp. Most amps have several multipliers in a row (aka in series or cascaded) so the relatively small signal coming from your guitar can be amplified and multiplied up to where the speakers run properly.

Adding more multipliers creates more preamp distortion. Generally, Boogie and Dumble amps have four gain stages, while earlier vintage amps used two preamp gain stages.”3.1”

Since the 1990s, a lot of amps have come out with four, five and even six stages of gain in their high gain channels, with increasingly sophisticated preamps offering three and even four channels. Higher gain channels really embrace the concept of preamp distortion, and go to great lengths to shape the guitar signal as it passes through the preamp to enhance a particular response the designer is shooting for — such as screaming compressed metal leads.

In most multi-channel amps, one channel (often channel two) is usually extremely similar to a JCM800. Channels three and above add more gain stages and processing to get those heavier metal tones.

Since they are, at least to some degree, ultimately inspired by the JCM800, a large majority of multi-channel amps are 100 Watts. Needless to say, unless you are a professional or really gung-ho, you will never turn the master volume up loud enough to get the power amp to distort.

Because modern amps have so much gain, regular players almost never feel the need to turn up the master volume, so they never hear or feel what Slash does. For this reason, the power amp effectively becomes a simple power-boosting device used to drive the speakers to moderate levels.

Digital or Modeling Amplifiers and Computer ProgramsA digital or modeling amp uses a computer in the preamp and transistors (tubes very rarely) in the power amp. The computer is loaded with programs that are mathematical models or simulations of the vintage and modern tube amp tones we have been discussing.

Depending on how much memory the amp has, you can choose from an infinite number of amp models. These models try to simulate analog amps as a whole — preamp, power amp and, quite often, speakers and cabinet.

The computer output is generally sent to a power amp that is supposed to act like a stereo amp and simply provide the power to drive the speakers (completing the removal of the power amp from the tone-generating part of the amplifier).

The power amp is the most expensive, most heat-producing and heaviest part of an amplifier. For these reasons, the de-emphasis of the power amp has been an engineering ideal at many companies. I sincerely hope they fail, as the loss of great power amp distortion is nothing less than a crime to the world of tone.

Using a modeling amp or a computer program like GarageBand to create electric guitar tones absolutely kicks ass for playing in your basement and making demo tracks. As an engineer and programmer, I applaud the technical

accomplishments in these products. But when it comes time to making a real recording or playing an actual gig, this technology is currently unable to replace the sound and feel of honest to goodness power amp, speaker and cabinet distortion.

The problem with computer amps is not just the digital versus analog issue, as with vinyl records versus CDs (although this is a factor). Without a dynamic power supply and other nuances in the analog gear, simulated amps can’t respond to you like an analog amp. Mathematical models are, after all, only approximations of real life.

Chapter Three Footnotes

3.1 Techno geeks will call me on this generalization. The Vibrato input — which should be labelled Tremolo — on Black and Silverface Fender amps has three stages of gain. But these amps have so much gain cut between the second and third gain stages that the overall amount of gain is similar to a two-stage preamp.

It’s when you strum your first chord on a calm Sunday morning and listen to the sound fade away… and suddenly everything comes into balance again.

Mikas Feigelovicius

Chapter Four—Great Recommendations

I’ve heard that if you put enough monkeys in front of enough typewriters, one of them will eventually write Hamlet. The same can be said of anything, I suppose. Fortunately some amps, from some surprising manufacturers, are right up there with Hamlet in the guitar world.

I have played a few amps over the years. The following are the amps I found to be outstanding. I have not played every amp in the world, so if I don’t mention yours, please don’t take offense.

Generally I like any vintage (pre 1973) tube amp I can get my hands on, so take that as a given. The suggestions in this chapter are for amps in current production.

Some of the suggestions are for vintage reissues originally made decades ago. The following list includes three modifications that will quite dramatically improve the tone of these reissues.

To improve The Tone of a reissued vinTage amp:• Have your tech replace the output transformer. If you can swing it, replace the power transformer as

well. Transformers are an easy place for manufacturers to cut corners. If you aren’t turning up the amp enough to get power amp distortion, you might not notice the difference (at least they are hoping you don’t).

Mercury Magnetics in Chatsworth, CA, makes original spec transformers (and more) that your tech can fairly easily install for you. Even if your amp is not a reissue, replacing the stock transformers with transformers for a compatible vintage amp can be just as helpful.

• Re-tubing and proper biasing are an absolute must. Lower end amps will usually come with lower end tubes. Installing good tubes can really perk up your tone. One large amp manufacturer was for quite some time purposely biasing power tubes extremely cold so they would last longer. (See “Chapter Five—Dowsing for Tone”).

• Putting a good speaker in a lot of these reissues can make a huge difference. Stock speakers, even if they have a well-known name on them, are often sub-par. (See “Chapter Five—Dowsing for Tone”).

Peavey Classic 30 and Classic 50What I respect most about Peavey is that they aren’t locked into vintage mojo ghosts that they have to live up to, so Peavey is free to experiment.

And experiment they do. Unfortunately, a lot of Peavey’s products have been less than well received by the high-end crowd over the years, even though some gear has been quite innovative.

The Classic 30 and 50 are amps definitely worth checking out. If you re-tube these babies and install an Eminence Governor, you just might start giving Hartley Peavey the kudos he deserves.

Peavey Transistor Amps As far as solid state amps go, there is no transistor amp on the planet better than a Peavey. Peavey specializes in the lower end of the market so they have substantial experience making transistors sound good. Put a Governor speaker in a Peavey transistor amp and you’ve got a great little practice amp for very little money.

Fender Reissue Tweed and Blackface Amps As opposed to Peavey’s inspired innovations, Fender amps seem best when the company sticks to its vintage designs. Most of their reissue amps, while not the same as the originals, are very good — especially if you tune them up with new transformers, new tubes and Jensen speakers.

Marshall 50 Watt Small Box Non-Master Volume Head

Have your tech tune this baby up with new transformers and good tubes and you are on the road to getting some great tones from Jeff Beck to AC/DC. Same goes for the 100 Watt non-master volume head, but it is just too frighteningly loud for me.

Marshall JCM800Have your tech tune it up, tease your hair and you are ready for some ’80s style rocking.

Vox AC30OK, so AC30s are made in China now, but with new Celestion Blues (which you can get stock), Tung-Sol 12AX7s and JJ EL84s, they still sound great.

Two Rock If you want Dumble-inspired yet more refined mojo, these amps are the ticket. Yes they are expensive, but not as expensive as real Dumbles, and the innovators at Two Rock have definitely improved on the original.

Tone KingI only heard one Tone King at a Gear Page amp fest in NYC; I have not played one. But I was immediately struck at the quality clean tone — absolutely fabulous.

MatchlessThis company is no longer owned by the founder, Mark Sampson, but it supposedly makes amps to his same design specs. Although these amps have a unique tone of their own, they do not mix well with a multi-amp set up. But alone, they are a great in-your-face rock amp.

TrainwreckKen Fischer’s amps are absolutely wonderful if you can get one ($10,000 last I heard since Ken has passed on). Trainwrecks offer a stunning mix of preamp and power amp distortion that no other amp achieves. Some people are supposedly making clones, but to my knowledge, Ken’s family has not licensed his name or designs to anyone. I hope that the family can find some decent folks to work with and that they will start making more of these babies.

Speaking of Decent FolksAs you may have noticed, many people in the music business live up to the stereotype of the quintessential crazy guitar store guy — more than a little scary. While I’ve come across my share of scary guys, I’ve also come across a lot of great people. The following list is the crème de la crème.

Guitar Player MagazineSan Jose, CAwww.guitarplayer.comGuitar magazines can be more than a little sketchy, but Art Thompson and the gear reviewers at Guitar Player are as knowledgeable, honest and thorough as they come.

Vintage Guitar MagazineBismarck, NDwww.vintageguitar.comIf you are looking for vintage or high end boutique gear, Vintage Guitar is definitely your first stop.

Rudy PensaRudy’s Music — New York, NYwww.rudysmusic.comOne of the most honest guitar aficionados you’ll ever meet, Rudy always carries the best new and vintage gear. My favorite is the funky old store off Times Square, while the new location in Soho is beyond cool. With soundproof demo rooms and a friendly, knowledgeable staff, Rudy’s is a must-stop when you’re visiting the Big Apple.

Buzz LevineLark Street Music — Teaneck, NJwww.larkstreetmusic.comBuzz has an eclectic collection of vintage and modern equipment in a relaxed, no pressure environment. With a wealth of over 40 years experience, Buzz loves to talk tone, your style, and how he can get the right gear in your hands. He’ll also let you crank an amp louder than just about any other music store owner I’ve had the pleasure of knowing.

Antique Electronic SupplyTempe, AZwww.tubesandmore.comAn excellent source for new and NOS tubes, speakers and quality electronic components. Their friendly, knowledgeable staff will go out of their way to help you find what you’re looking for at the right price.

Billy ZoomGuitarist for X & Amp Tech — Los Angeles, CAwww.billyzoom.comBilly is not only a master guitar player, he is an equally masterful amp tech. If you need amp repairs, tune-ups or tone upgrade suggestions, Billy will treat you right.

Don ButlerGuitarist for Working Class Hero & Amp Tech — Los Angeles, CAwww.tone-man.comWith over 25 years of hands-on experience as an amp tech and professional musician, Don is one of the best in the business. He offers repairs, mods, general maintenance and restorations to tube amps, guitars and effects pedals.

Kevin HastingsAmoskeag Woodworks — Essex Junction, VTwww.amoskeagwoodworking.comWith a state brimming with master cabinet craftsmen, Kevin shines above the rest as the most talented, the most professional, the most precise and downright easiest guy to work with. If you’re even thinking about getting a custom cabinet made, don’t make any decisions without talking to Kevin.

Phill TomenyAll Seams Fine — Waterbury, [email protected] all know that working with leather can be a nasty business (or then again, maybe not). Phill has mastered the art of sculpting leather, tolex and any other type of cloth-like substance you can imagine. When he’s not deftly covering, recovering and repairing amp cabinets, Phill spends his time restoring high-end very cool antique car interiors, as well as singing and playing lead for Vermont’s own Phill ’n the Blanks. If you have an amp, car or local event that can use some magic, Phill is your mann.

Playing my guitar is the one time i know i’m truly connected to “source”… to God… to “all that is” in the universe.

When i get out of my own way… when i leave behind my judgment, ego, fear, distraction and a host of other things that plague us as humans… and just PLAY, it creates a powerful meditative space where my purest thoughts and feelings are freely expressed and i experience a joy and a release like at no other time in my life.

i live for those moments of precious, artistic & spiritual connection.

Life is not about waiting for the storm to pass, it’s about learning to dance in the rain…

Mark KaranBob Weir & Ratdog

Mark Karan & Jemimah Puddleduckwww.markkaran.com

Chapter Five—Dowsing for Tone

You can easily modify your amp’s tone and character yourself — beyond turning the knobs — with a few tweaks, some simple, some not so much. Of course, having your tech mod or rebuild your amp will certainly have the most dramatic effect on your amp’s tone. So with the exception of the last two options, Figure 5.1 shows the tweaks you can make with and without your tech, in descending order of the impact each tweak will have on your tone.

WITHOUT your tech you can

WITH your tech you can

Cultivate your style Add a sag modification

Change speakers and cabinets Change the output transformer

Change power tubes (self-biasing/external-bias only)

Change power tubes”5.1”

Change preamp tubes Add your tech’s suggested mod

Replace cords and cables Rebuild your amp

Figure 5.1 Tonal Tweaks

Cultivating Your StyleBefore googling a local tech, you can do quite a lot to improve the tone of your existing amp by understanding your technique and how it relates to your amp. “Chapter Six—Cultivating Your Style” explains what you can do to begin right now.

Changing Speakers and CabinetsWhile working on your tone, the next tweak that will have the most impact on your amp’s tone includes new speaker(s) and/or cabinet(s). Stock speakers, especially on cheaper amps (less than $1500) can usually benefit from a good upgrade.

The following section explains how to change a speaker in your cabinet. “Chapter Seven—Speakers” discusses speakers in detail, including individual speaker tone (to help you decide which speaker(s) you’d like to try). “Chapter Eight—Cabinets” will help you decide which type of speaker cabinet is best for you.

Replacing a SpeakerSpeakers have slip on/off electrical speaker wire connections, so you can gently pull the wires off. Sometimes, for a more secure connection that won’t corrode over time (like slip on/off connections tend to do), speaker wires are soldered to the speaker terminals.

To replace a speaker with soldered wires, you will need a soldering iron and a solder sucker. If you don’t have these tools, you may want to consider having your tech change the speakers for you.

0 WARNINGRead “Chapter Sixteen—Safety Basics” before breaking out the soldering iron.

To remove a speaker:1. Check to make sure the amplifier’s power switch is in the Off position.

2. Determine which wire is connected to which speaker terminal (labelled + and -) before you begin, and make a note of it.

3. Disconnect the wires going to the speaker(s).

4. For cabinets with studs permanently installed into the baffle board, remove the nuts and lock washers that are screwed onto the studs. Skip to step #5.

For cabinets using wood screws, remove the wood screws that go through the speaker mounting holes and thread into the wooden baffle board.

5. Gently lift the speaker off the baffle board, applying force evenly so you don’t bend the speaker and/or studs. The speaker has a gasket around its outer edge so that good contact is made with the baffle board (see “Figure 7.4 AlNiCo vs Ceramic speaker magnets” ). Over time, this gasket can get quite stuck to the baffle board, so use caution when you first lift the speaker.

To insTall a speaker inTo a cabineT WiTh sTuds:1. Slip the speaker over the studs onto the baffle board, applying force evenly so you don’t bend the speaker

and/or the studs.

Although the speaker-mounting holes forCelestion and Jensen speakers are supposed to be compatible, I have found that they are close, but no cigar. I usually end up running a rat tail file through the Jensen speaker-mounting holes to open them in the direction of the edge of the speaker. The filings like to stick to the speaker’s metal basket, but you can easily wipe them off with a damp cloth.

Ω WARNINGBe very careful not to poke a hole in the speaker cone. Once the cone has a hole, it can’t be fixed… unless you’d like to try the Kinks’ trick on Girl You Really Got Me; they purposely cut up the speaker cones to get distortion.

2. Check to make sure the speaker’s spongy gasket is flat against the baffle board. This step is important to prevent unwanted noise.

3. Thread the nuts and lock washers onto the studs.

4. Match the correct speaker wire to the correct speaker terminal, and slip on or solder these connections.

To insTall a speaker inTo a cabineT using Wood screWs:1. Line up the speaker screw holes with the baffle board screw holes.

2. Check to make sure the speaker’s spongy gasket is flat against the baffle board. This step is important to prevent unwanted noise.

3. Insert the wood screws through the speaker mounting holes and thread into the wooden baffle board.

4. Match the correct speaker wire to the correct speaker terminal, and slip on or solder these connections.

Connecting Speakers — Series and ParallelYou can connect two speakers to one amplifier using either a series or parallel connection. Figure 5.2 illustrates how to use both types of connections.”5.2”

With a series connection, the plus from the amplifier (tip of the ¼" plug) goes to the plus terminal of the first

speaker. The minus terminal of the first speaker gets wired to the plus terminal of the second speaker, and the minus terminal of the second speaker goes to the minus of the amplifier (sleeve part of the ¼" plug).

With a parallel connection, the plus from the amplifier (tip of the ¼" plug) goes to the plus terminals for both the first and second speakers. The minus terminals of both the first and second speakers go to the minus of the amplifier (sleeve part of the ¼" plug).

Power Delivered to Individual Speakers in a Multi-Speaker CabinetLet’s say you have an eight Ohm Blue Speaker (rated at 15 Watts) and a 16 Ohm P12N (rated at 50 Watts), and you want to connect these speakers to your 50 Watt amplifier.

Figure 5.2 Wiring for Series and Parallel Connections

your quesTions are:

• How should I connect these speakers to each other?

• What should I set the amp’s impedance selector to?

• How many Watts will be delivered to each speaker?

These questions are frequently asked and need a clear answer. You will find an easy reference chart in “Appendix A—Speaker Ohm Charts” covering all your impedance calculation needs.

Power is distributed to the speakers based solely on impedance (Ohms), not on power rating. Use the chart by first determining how much power is going to each speaker, and then compare this power to each speaker’s maximum power rating to make sure you don’t blow anything up.

For your convenience, the impedances charts in “Appendix A—Speaker Ohm Charts” are for 30, 50 or 100 Watt amplifiers. For marketing reasons, a lot of amps that would have been labelled 50 or 100 Watts in the ’60s and ’70s are now labelled 60 and 120 Watts, respectively. Rest assured that an amp labelled 100 Watts in 1970 is undoubtedly more powerful than an amp labelled 120 Watts today. So go ahead and use the 50 and 100 Watt charts for amps labelled 60 and 120 Watts.

If you have a 200 Watt amp, like a Marshall Major, double the Wattages in the 100 Watt amp chart.

Going back to the question of how to connect a Blue and P12N to a 50 Watt amp, the chart for a 50 Watt amplifier shows that your only choice is to connect the Blue and P12N in series.

With a parallel connection, the eight Ohm Blue receives 33.3 Watts, and the 16 Ohm P12N receives 16.7 Watts. While the P12N can certainly handle 16.7 Watts, the Blue is rated for 15 Watts, so a parallel connection sending 33.3 Watts will blow the Blue, (although exceeding a speaker’s rated Wattage a little bit is generally okay, especially when using a closed back cabinet).

With a series connection, the charts show that the Wattages delivered to each speaker are reversed, with the Blue receiving 16.7 Watts, allocating the remaining 33.3 Watts to the 50 Watt P12N.

You can see that the exact impedance of these two speakers in series is 24 Ohms. For maximum power, select the impedance on your amp closest to your speaker cabinet’s impedance setting — in this case, the 16 Ohm setting.

Lowering Volume with Half Power and Mismatching ImpedancesWhen the speaker’s impedance matches the amplifier’s impedance, one half of the total power the amp makes is

dissipated in the amp. The other half of the power goes to the speakers.

Mismatching impedances is one way to lower the volume of your master and non-master volume tube amps and still get power amp distortion. However, you can only mismatch when you are running your tube amp at half power.

0 WARNINGWhen mismatching impedances, run your amp at half power or you can easily blow your amp.

four Ways you can loWer volume by running an amp aT less Than full poWer:• Turn down the Wattage control (if available) — unfortunately, this method reduces power supply sag

on most amps.

• Turn down the Master Volume knob (if available) — unfortunately, this method reduces power amp distortion on all amps.

• Refrain from pushing your non-master volume amp anything close to distortion.

• Remove one pair of power tubes (of course, this option only applies to amps with two or more pairs of power tubes).

Mismatching impedance, either higher or lower, causes more than half the power your amp is producing to be dissipated in the amp. But because you are running the amp at less than full power, the added power/heat is okay.

The flip-side is that less than half the power the amp is making goes to your speakers, lowering your volume — a great tool to have on a non-master volume tube amp!

Removing Tubes and OhmsWhen you remove one pair of power tubes from a two pair amp, you double the amp’s output impedance. So an amp with four, eight and 16 Ohm outputs becomes an amp with eight, 16 and 32 Ohm outputs.

The greater the impedance mismatch, the more the power going to the speaker is cut. For example, a four Ohm speaker connected to the 32 Ohm output (labelled 16) causes the maximum mismatch and the lowest possible volume. Using a four Ohm speaker with the eight or 16 Ohm outputs is considerably louder.

Go ahead and experiment with different amounts of mismatching to see what works for you, but always remember, do not go to maximum power with the power amp or you will blow things up!

Changing Power TubesLike light bulbs, power tubes burn out and need to be routinely replaced and rebiased depending on how often you play your amp. Some amps allow you to replace the power tubes yourself, while most do not.”5.3” This is too bad, because changing the power tubes can have a dramatic affect on tone, not to mention the inconvenience and cost of visiting your tech for routine power tube maintenance.

Biasing sets the idling current in the tubes, which is similar to setting the idle on your car. How your amp’s power tubes are biased determines whether or not you can change power tubes yourself. Cathode bias, like an automatic transmission, automatically rebiases so you can basically plug and play. External bias allows you to bias the tubes from an external interface on the amp. Internal bias requires that the chassis be removed from the cabinet. Because lethal voltages are involved, your tech needs to bias this type of amp for you.

For more information on biasing, see “Biasing the New Power Tubes”. To determine which tube flavors you’d like to try, refer to “Chapter Nine—Power Tubes” and “Chapter Ten—Preamp Tubes”

Removing Power TubesThe power tubes in your amp are most likely held in place with some type of tube retainer.

The Three basic Types of reTainers are:• Base Clamp Retainer

• Spring Retainer

• EL84 Retainer

The Base Clamp RetainerBase clamp retainers only accept small base power tubes, such as 6V6s, 6L6s, EL34s and KT77s. If you’d like to install large base octal tubes (such as KT66s, KT88s or 6550s), have your tech replace the base clamp retainers with spring retainers, which accept both large and small-based octal tubes.

The base clamp retainer looks like an open clam shell and has two small teeth on each side to help grip the base of the power tube.

Figure 5.3 Base Clamp Retainer with tube

0 WARNINGRead “Chapter Sixteen—Safety Basics” before removing or installing power tubes.

To remove a Tube from a base clamp reTainer:1. Check to make sure that the amp is off and that the tubes are cold.

2. Spread the two sides of the clam shell apart toward the chassis and away from the tube using two fingers from one hand.

3. Pull the tube out of the socket with your other hand. You can rock the tube back and forth a little to get it going, but too much will break the tube locator pin.

The Spring RetainerA spring retainer has two springs going from the chassis to a round metal plate with a hole in the middle called the retainer.

Figure 5.4 Spring Retainer with tube

To remove a Tube from a spring reTainer:1. Check to make sure that the amp is off and that the tubes are cold.

2. Grab each side of the retainer and pull it away from the tube, letting go to allow the retainer to hang to the side.

3. Pull the tube out of the socket with your other hand. You can rock the tube back and forth a little to get it going, but too much will break the tube locator pin.

The EL84 RetainerThe EL84 retainer is a variation of the spring retainer, but without springs. Instead, bent spring wire goes up and over the tube. The tube itself has a pointed end built into the glass that fits into the retainer. Figures 5.5 and 5.6 show an unloaded and loaded spring retainer; the retainer springs in your amp may be oriented as shown or turned 180°.

Figure 5.5 EL84 Retainer

To remove an el84 from The reTainer:1. Check to make sure that the amp is off and that the tubes are cold.

2. Grab the curly tip end of the retainer, pull down, and rotate toward the side of the tube that most of the retainer wire is on (this keeps the end of the wire near the tube base from becoming entangled with the tube pins).

3. Release the retainer.

4. Pull the tube straight out of the socket. You can rock it a little side to side to help dislodge it, but too much rocking will bend the pins.

Figure 5.6 EL84 Retainer with tube

Installing New Power TubesOnce you have your old tubes out, you’re ready to put in new tubes. However, you must be very careful about how you place the tubes in the sockets — there is only one right way, and you can easily bend or break a pin.

Figure 5.7 Bottom of octal power tube showing the Locator Pin

Figure 5.8 Top of octal power tube socket showing the Locator Pin’s female match

Octal Power TubesLarge power tubes have eight metal pins3 (as shown in Figure 5.7), arranged in a circle around a larger round plastic pin with a tab called a locator pin. Because of the eight pins, these tubes are called octal power tubes. With the one exception of EL84s, all the power tubes you will likely encounter will be octal.

To insTall an ocTal poWer Tube:1. For amps with base clamp retainers, gently push the two sides of the retainer toward the chassis using

two fingers. Skip to step #2.

For amps with spring retainers, move the retainer to the side with one hand.

2. Use the locator pin to determine which way to place the tube in the socket. The socket will have a female center hole that accepts the locator pin, ensuring you place the tube in the correct position (Figure 5.8).

0 WARNINGIf a tube is incorrectly placed in a socket, it can short out the electronics, causing damage to internal components. If this happens, you will definitely be visiting your tech. Use caution when lining up the locator pin.

0 WARNINGDo not attempt to use any tube with a missing or broken locator pin. You will simply be playing Russian roulette with your amp.

3. Using your free hand, gently press the tube straight into the tube socket. Wiggle the tube back and forth a little to ensure a tight fit. When you’ve got the power tube in correctly, you will not be able to see space between the tube and the socket — the fit should be snug as a bug. If you find that you have one socket that never fits snugly no matter which tube you use, have your tech re-tension the socket pins for you.

4. Wipe off the glass on the tubes with a soft clean dry cloth after you install them. Oils from your hand weaken the glass as the tube heats up.

Nine Pin TubesEL84s look like extra long preamp tubes with nine pins (arranged just like a preamp tube). EL84s and preamp tubes are called nine pin tubes because they both have nine relatively thin pins arranged in a circle that looks like it should have a tenth pin.

The pins are very thin and bend easily. If the pins are bent, you can use needle nose pliers to straighten them out. Just remember that the pins are embedded in a glass tube, so be careful.

Nine pin tubes do not have a center locating pin; instead, the lack of the tenth pin is used as the locating device.

Figure 5.9 Nine pin 12AX7 preamp tube

Figure 5.10 Nine pin tube socket

EL84s cannot replace a preamp tube or vice-versa. Interchanging these two tube types is another opportunity to short out the electronics, causing damage to internal components and a visit to your tech.

0 WARNINGEL84s power tubes are not interchangeable with preamp tubes. Interchanging these tube types will short out internal electrical components.

To insTall an el84:1. Check to make sure that the end of the retainer is not tangled in the tube pins.

2. Insert the EL84 making sure that the missing pin on the tube lines up with the missing hole in the socket. When you’ve got the power tube in correctly, you will not be able to see space between the tube and the socket — the fit should be snug as a bug. If you find that you have one socket that never fits snugly no matter which tube you use, have your tech re-tension the socket pins for you.


4. Double check that the tube base end of the retainer wire is not mixed in with the tube pins on each side of the retainer.

5. Bend the tabs holding the retainer wire to the base away from the base a bit if there are clearance problems.

6. Pull the retainer wire’s curly tip end up and over the tube tip and gently release it.

Once you have the new power tubes in, you’re ready to bias.

Biasing the New Power Tubes Amplifiers offer one of three biasing methods.

• Cathode bias

• External bias

• Internal bias

Cathode BiasIf your amplifier is cathode bias (or self-biasing), you can start playing!

External BiasIf your amp offers an external bias feature, follow the manufacturer’s instructions for biasing the tubes.

High-end external bias features allow you to bias each tube individually. This feature is very cool as no two tubes are ever truly matched (and if they are, they certainly don’t stay matched as they wear in).

When biasing externally, keep in mind that the manufacturer’s recommended bias settings are not exact. Lower amounts of bias current (biasing your tubes cold) result in a thinner, cleaner tone and give your tubes a somewhat longer life. Higher amounts of bias current give your amp a fatter sound that is easier to push into distortion (but of course your tubes will have a somewhat shorter life).

However, limits exist on how far you can adjust the bias current for each tube. If you set the bias current too high, the plates (the metal part of the tubes that you can see) will glow red hot, first in spots, and then all over as you turn up the current.

Some players like to increase the bias current until the tubes begin to glow a little, and then back off just a bit. While this can result in good tone, for safety reasons I highly suggest measuring the bias current and not exceeding the

amp manufacturer’s recommended maximum settings for each tube.

0 WARNINGAlways bias within the amplifier manufacturer’s recommended bias settings. Running the tubes too hot can cause a fire at worst, or burn out your tubes quickly at best.

Of course, you can set the bias current a bit lower than the manufacturer’s recommended maximum setting, but not much lower. As shown in Figure 5.11 the output tubes run in two groups, with the right group amplifying the positive half of the signal, and the left group amplifying the negative half. If the bias current is too low, a gap develops at the crossover point where the positive amplifying tubes turn off before the negative amplifying tubes turn on (shown in Figure 5.12). This gap in the signal is called crossover distortion, and believe me, this type of distortion is no fun.

Figure 5.11 Typical Sine Wave

Figure 5.12 Sine Wave with Crossover Distortion

So biasing your amp either too hot or too cold can cause problems. However, you do have a range to play around in. For example, in a Ganesha the range of acceptable bias currents is between 15mA and 40mA for a 6L6, and between 10mA and 30mA for an EL34. Going higher than these ranges will cause the tubes to glow red in spots (severely lowering the life of the tube); going lower will cause crossover distortion.

Power tubes have a break-in period of about 40 hours; after that they need re-biasing. As each tube ages, it will occasionally need to be adjusted until it will eventually no longer be able to produce enough current to operate properly.

Internal BiasAmps without self or external biasing features require that your tech remove the chassis from the cabinet in order

to measure and adjust the bias current. Because biasing needs to be performed while current is running through the tubes, internal biasing involves measuring lethal voltages and should only be performed by an experienced technician.

0 WARNINGIf your amp is not cathode biased (self-biasing), and does not offer an external biasing feature, it needs to be taken to your tech for power tube changes. The bias currents involve measuring high voltages that are lethal. For internal bias amps, have your tech change your power tubes for you.

Changing Rectifier TubesRectifier tubes wear out, just like power tubes. Replacing a rectifier tube is the same as replacing a power tube, except you don’t need to worry about biasing.

A new rectifier tube will give your amp a punchier, louder tone, so having various types and ages of rectifiers around is another way to fine-tune your tone.

like poWer Tubes, recTifier Tubes run very hoT. alWays remember To:1. Check to make sure the amp is off and the tubes are cold.

2. Clean the tubes with a clean dry cloth after installation to remove any oils from your hands.

Changing Preamp TubesChanging preamp tubes is similar to changing EL84s (they both have nine pins) in a self biasing amplifier. The only difference is that preamp tubes do not have retainers — instead they hold themselves in place through the friction of the pins in the socket.

Figure 5.13 High-end preamp tube shield showing shield slot and base notch

However, preamp tubes on high quality amps are covered with a metal shield designed to keep noise from getting into the tube. These shields are not meant to be retainers, but they certainly do function as such.

0 WARNINGRead “Chapter Sixteen—Safety Basics” before removing or installing preamp tubes.

To remove The preamp Tubes:1. For amps with preamp tube shields, push the shield toward the amp chassis.

For amps without shields, skip to step #3.

2. Give a little 1/8 twist counterclockwise to detach the base notch from the shield slot. The shield will fall right out.

3. Remove the preamp tube gently, taking note of where the gap in the nine pin socket is (which can be difficult to see with a tube shield base around it).

To insTall preamp Tubes:1. Match the missing socket hole with the missing tube pin and carefully insert the preamp tube into the

socket.


3. For amps with preamp tube shields, slide the shield over the tube making sure the inside spring fits over the tip of the tube.

For amps without shields, skip steps #4 and #5.

4. Vertically match the shield slot with the base notch.

5. Gently turn the shield approximately 1/8 turn clockwise until it snaps into place.

Replacing Cords and CablesCords and cables can make more of a difference to your amp’s tone than you might think. Check out “Chapter Eleven—Cords and Cables” for details on how different types of cords affect tone.

Adding a Sag ModificationSag mods require serious surgery, but they will get you toward a smoother, more vintage tone, even with a modern high gain amp. Sag options include adding a rectifier tube or the magic resistor.

Tube RectifierIf you are up to buying a new power transformer, have your tech modify the power supply of your amp to use a tube rectifier instead of solid state. Adding a tube rectifier will add a significant amount of sag, and therefore smoothness, to your amp when pushed. A rectifier will also lower the volume at which the power amp starts to break up.

Conversely if you have a tube rectifier, you can use a solid state replacement that plugs into the rectifier tube socket for a punchier, louder amp.

Magic ResistorIf you would like to make your amp saggier without changing the power transformer and adding a tube rectifier, have your tech add the “magic resistor.” You can find technical instructions in Fizz Kill-How to Kill Output Transformer Ringing/Fizz and Attenuator Created Blowouts With One Stone available from amazon.

• For amps with two power tubes, add a 50 Ohm 25 Watt power resistor between the solid state rectifiers and the filter caps.

• For amps with four power tubes, add a 22 Ohm 50 Watt power resistor.

0 WARNINGDo not allow your tech to add a big fat potentiometer (aka a pot or variable resistor) on the front panel of your amp to give you control over sag. Unlike treble or bass, the voltages involved with power supply sag are lethal. Although this method is technically legal because of manufacturers’ pot ratings, placing high voltages on a user control is simply not the safest method available.

Changing the Output TransformerChanging the output transformer (OPT) is a very effective step you and your tech can take to change your amp’s tonal character. The results can be quite dramatic, especially when you’re pushing your amp into power amp distortion.

http://www.amazon.com/Kill-How-Transformer-Attenuator-Blowouts-Amplifier-ebook/dp/B004YLOB7O/ref=sr_1_1?ie=UTF8&qid=1407225640&sr=8-1&keywords=fizz+kill+dave+zimmerman+guitar+amplifiers

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Mercury Magnetics makes excellent, smooth responding OPTs for just about every type of amp. If your amp isn’t on their list, they can help you find a substitute that meets your needs.

For example, let’s say you have a Fender Blues Deville. For overall better tone, you could replace the OPT with one made for a Blackface Super Reverb. Or, if you want a more compressed tone, you could use an OPT for a Tweed Bassman. If you want to get really creative and move away from the mushy bass that Fenders generally have, you could try the OPT for a Marshall 50 Watt Plexi, (but you will probably find yourself backing off on the bass).

Be careful with the output impedance settings when using a different OPT; you might have to rewire your speakers to match the impedances your new transformer offers.

Adding Your Tech’s Favorite ModDepending on your amp and the level of your tech’s experience, you may be able to have your amp modified (aka modded) to make the tone more to your liking. While a mod can’t completely change your amp, it will definitely affect the voicing (the frequencies that are accentuated or diminished), and sometimes the gain. A mod can be successful at reducing your amp’s gain, but increasing gain is a bit more difficult.

Rebuild Your AmpIf none of these tweaks works for you, start thinking about a whole new amp. If you are in love with your amp’s look, you can also think about having your tech completely gut the inside and rebuild it (although you might find that a whole new amp is far more cost effective). Techs often enjoy the challenge and freedom of completely redoing your amp for you, and will work hard to get it just where you’d like.

Chapter Five Footnotes

5.1. When you change a power tube, you need to rebias, or set the idling current. Some amps have Cathode Bias (self-bias) which automatically rebiases the tubes for you. Others offer an external bias adjustment that allows you to easily bias from the back panel. Never try to bias an amp that does not have one of these features without the help of your tech.

5.2. Figure 5.2 is conceptual representation of series and parallel speaker connections. The physical wiring in your cabinet will appear differently.

5.3. Figure 5.7 shows a kinkless tetrode 6V6 bottom, an octal tube which does not require all eight pins to operate. Depending on the tube type or manufacturer, an octal power tube can have six, seven or eight pins. An octal rectifier tube usually has five pins, but can have up to eight.

When I pick up my guitar I feel like an artist looking at a blank canvas. At that exact moment there are no rules. I have the freedom to express what I can’t with words. It’s an escape to a timeless world; a place that I can show whatever emotion I am feeling and I have my own personal language where everything makes sense. The guitar is my brush and my amplifier is the paint. The combination of these two pieces allows for a type of meditation and freedom I can’t get anywhere else. As Jim Morrison said, “the music is your special friend.”

Andy Meade

Chapter Six—Cultivating Your Style

A good amp, regardless of how distorted, responds to your touch. True responsiveness (as opposed to touch sensitivity) is easiest to feel with low gain non-master volume amps. Great non-master volume amps produce gorgeous cleans when you back off your touch, and they allow you to dial in a large amount of gain variation via the Volume knob on your guitar.

However, a good master volume amp can also be very touch responsive — as opposed to just on or off, which some manufacturers market as a feature called touch sensitivity.

Playing a Non-Master Volume AmpIf you are under 40 years old, you most likely have never been face-to-face with a non-master volume amplifier, which is unfortunate. I would like to help prepare you for the day when you encounter one.

Long ago in the dark ages when cars had fins and we could Just Say Yes, amplifiers had only two, perhaps three, knobs: Volume, Tone and maybe Tremolo and/or Reverb. If you were lucky, you had Bass and Treble knobs instead of a Tone control. Your amp was really cool if it had a Mid knob. In all cases, all amps had vacuum tubes (known as valves in Europe).

When confronted with either a vintage or reissue amp, too many guitarists simply have no idea what to do. Modern master volume amps have knobs labelled Gain, Pre, Distortion, Drive or something along these lines, and a knob labelled Volume, Post or Master. Vintage amps have no Gain knob or Master knob, but they do have a Volume knob, often near the input jack where the Gain knob should be on a modern amp. Where is the knob labelled Master? Where is the Gain knob? Why is the Volume knob in a strange place? How come this amp looks so different from what I am used to and how do I make it work?

When guitar amplifiers were first created, manufacturers believed only clean sounds were desirable. So amps were made much like home stereos, with only tone controls and a way to control the amp’s overall volume.

Vintage amplifier circuits tended to be very simple derivatives of the sample circuits shown in tube manufacturer manuals (in particular the RCA Receiving Tube Manual). In those manuals, the input sensitivity of amp circuits was geared more for phonograph inputs than for the higher outputs available from electric guitars. Luckily, these circuits made overdriving the amp beyond clean pretty easy.

It didn’t take guitarists long to realize that cranking the amp’s Volume knob not only caused the amp to become louder; it also caused the amp to behave differently. As you turn up a vintage amp’s Volume knob, sustain increases; the tone changes and distorts in a way that allows the amp to be more expressive, responsive and alive.

So with the amp’s and/or the guitar’s Volume knob turned down low, vintage amplifiers produce a clean tone, and the sound coming out of the speakers is very similar to what the guitar sounds like alone.

As you turn up the amp’s Volume, the amp starts to sound “thicker,” as if more energy is coming from the speaker than what you put into it. This thicker tone would still be classified as clean, but the amp is more expressive and feels more responsive and alive.

This clean is what you hear on a lot of Country and Jazz albums, as well as Jimi Hendrix, and is more than a sterile

http://www.amazon.com/Receiving-Tube-Manual-RC-30-Reprint/dp/B000TNHBAU/ref=sr_1_1?ie=UTF8&qid=1407803855&sr=8-1&keywords=RCA+Receiving+Tube+Manual

plunking at low volume. It’s a tone that has not yet been pushed to the point of having just a tad of “hair” or dirt on it. Clean is when you have pushed the amp to just below its limit, and your guitar is sustaining and singing without losing its voice.

The cabinet is also shaking quite a bit (as it should) and moving a lot of air (in addition to the air being moved by the speakers), creating a kind of natural reverb. At this point, the amp is louder than you think, so please wear earplugs and stand back.

With this clean tone, many if not all, of the major systems in the amp have gone beyond their strictly linear (perfect reproduction) region and are just beginning to add harmonics. But, they aren’t being pushed so hard as to cause clipping (see “Chapter Fourteen—Distortion Basics”).

As you turn up the Volume even further, the amp starts to break up, otherwise described as having “hair” on the note or getting dirty or crunchy (depending on how your particular amp responds). The amp begins to sustain even more, and produces that bluesy early Zeppelin, AC/DC, Rolling Stones, Jack White tone. It feels growly and in-your-face, yet still articulate. Of course, at this point, the amp is pretty damn loud.

Some of the major parts of the amp are now starting to clip the signal. By being careful with your amp’s Volume adjustment (using your guitar’s Volume knob will come in handy here) you can play around with just how crunchy the amp sounds — or in technical terms, just how much the amp is clipping.

At this point, your amp can’t get significantly louder than it was one number lower on the Volume dial. Once clipping starts, you can only add more distortion.

This phenomenon is the most important aspect of non-master volume amps. The Volume knob(s) act like the Volume knob on your stereo only up to a certain point — the point of clipping. After the amp reaches clipping, the Volume knob becomes a Distortion knob.

A good approach to making clean tones with a non-master volume amp is to start with a crunchy tone.

To dial in faT clean Tones WiTh a non-masTer volume amp:1. Set the guitar’s Volume knob all the way up.

2. Adjust the amp’s Volume knob(s) to the crunchy/distorted sound you like.

3. Back off on the guitar Volume. The tone will back down to the clean sound again.

Voilà, a two channel amp at your disposal and you didn’t even need a footswitch!

An amp that responds well to the guitar Volume is said to clean up well when you back off. Of course, with a non-master volume amp, you can also back off by simply playing more lightly, which is magical all by itself.

Depending upon the gain available with the particular amp you have and how hot your guitar is, you can turn the amp’s and guitar’s Volume knob(s) up even higher and the tone will be more distorted but at the same time more smoothed out — a violin-type of sustain as opposed to the crunchy in-your-face tone at lower Volume settings. Examples of sustainy, smooth distortion are Cream, Jeff Beck, Eric Johnson and the Allman Bros.

So, if you are really good with your touch and guitar Volume techniques, you can get three very different tones from a non-master volume amp, all without having to wear your tap shoes.

Sometimes using your guitar Volume can be frustrating because backing off on your guitar can cut a lot of high end, making the cleans dead and lifeless. Some players add brightness caps to the guitar’s Volume controls to compensate for this problem.

I can’t say one positive thing about brightness caps. They make humbuckers sound as thin as single coils, and generally completely change the character of the guitar with the Volume knob turned down. Nevertheless, I respect that some players like them. But if you find yourself truly frustrated by your guitar’s Volume knob, a buffered volume pedal is a better way to go.

Spending some quality time learning how to tame a non-master volume beast can really help your understanding of all amplifiers. With your earplugs and favorite guitar, try to get alone in a soundproof room with a 50 Watt Marshall Plexi or Fender Tweed Twin (reissues of course) at your local Guitars’R’Us.

Jumping Channels in Vintage or Reissue AmpsSpeaking of those reissue amps, I should take a moment to talk about jumping channels in vintage-style amps.

Many vintage-style amps have two channels, with each channel having its own two inputs. These two channel amps do not behave the same way that modern channel switching amps do. Instead, channels on vintage-style amps are separate, relatively equal input points, internally mixed together after each input has gone through its own separate first gain stage and separate Volume knob — but before the last preamp gain stage and tone controls. Generally one of the channels will be brighter than the other.

This arrangement is called jumpered channels and is equivalent to plugging into both channels at once.

The idea behind multiple channels on vintage amps was to give you the ability to plug your guitar, your cousin’s bass and your sister’s accordion all into one amp for a ready-made rock n’ roll band. This was possible because each channel had two input jacks tied together through a relatively small resistor.

But what guitarists quickly found was that they could plug into both channels simultaneously. Jumpering channels allows you to blend both channels together to make your tone just right by mixing the two channels using their respective volume controls.

To play an amp WiTh jumpered channels:1. Plug your guitar into the main input on one of the channels.

2. Take a short guitar cord (aka a patch or jumper cord) and plug one end into the second input of the same channel you plugged your guitar into.

3. Plug the other end of the jumper cord into the main input on the other channel.

4. Use both Volume knobs to mix together the normal and bright channels to get the sound you want. When you want to crank the amp, you’ll need to crank both Volume knobs.

Whenever you see someone playing a non-master volume Marshall, it will almost always be set up this way, since each channel on its own is a little too bright or a little too dark.

Playing a Master Volume AmpAn amp with a Master Volume knob can be approached in two ways.

The usual approach To using The masTer volume knob is:1. Turn the Master Volume knob all the way down so that you are playing quietly.

2. Turn the Gain knob up until the amp is screaming enough for you.

This approach is certainly fun and doesn’t involve blowing your ears out. The next approach is to treat your master volume amp is if as it were a non-master volume amp.

� WARNINGPlease wear earplugs when turning up the Master Volume knob.

To play your masTer volume amp as if iT Were a non-masTer volume amp:1. Turn the gain up very little, say to one or two.

2. Turn the Master Volume knob up to as loud as your practice space will allow to get the whole amp cooking, not just the preamp.

3. Add thickness, sustain and compression to your tone by turning up the gain on the preamp.

While this approach is definitely louder, it allows for more organic sounds, and the overall tone will be fatter and more engaging.

One good Guitar plus one good Amplifier makes this reserved Brit Rude and Nasty! Kerrang!

pete trisonic

Chapter Seven—Speakers

Speakers and cabinets can be some of the most frustrating components to deal with, both for players and for manufacturers. Choosing the right speaker for the right application can create a wonderful synergy that gets you exactly where you want to go; choosing the wrong one can make you feel like you have made some serious errors selecting your equipment.

The reason for all this consternation is that guitar speakers and cabinets are fundamentally different from stereo speakers and cabs. Guitar speakers/cabs offer a much wider tonal palette.

four main areas Where guiTar and sTereo speakers differ: • Frequency response

• Efficiency

• Power handling capability

• Cabinet resonance (covered in “Chapter Eight—Cabinets”)

Frequency ResponseThe goal in designing a stereo speaker is to change (or transduce) the electrical signal coming from the amp into identical looking sound pressure waves. The goal in designing a guitar speaker is much more complicated. With a guitar speaker, some frequencies are accentuated over others, and the really high end of the frequency spectrum is rolled off completely.

Most guitar speakers have a somewhat flat — meaning even or equal to — frequency response from around 80Hz (your low E string) to around two kHz (which is a little above the fundamental of E on the 24th fret of the high E string).

However, somewhere between two and four kHz, most guitar speakers’ output for a given input rises dramatically, producing a treble boost which is generally very desirable. The exact shape of this treble boost makes a big difference in tone.

For example, a Celestion Vintage 30 has a treble boost region starting much lower than a G12H30, and the Blue speaker has an even higher frequency treble boost area. To see the exact shape of an individual speaker’s frequency response curve, refer to the manufacturer’s web site.

Depending upon the cabinet, the rest of your gear and your touch, one of these speakers will work better than the others. In an open-back cabinet, the Vintage 30 can sound much honkier than the G12H30 or the Blue due to the lower frequency of the boost region. But in a closed-back cabinet, this wide region of boost frequencies can make for a fatter sound. For these reasons you will generally only see Vintage 30s (which actually handle 70 Watts) in closed-back cabinets.

EfficiencyThe other big difference between stereo speakers and guitar amp speakers is efficiency. Efficiency is an engineering term referring to how much electrical energy goes in versus how much sound wave energy comes out. Efficiency is measured by how loud a sound (in dB) from one speaker is with one Watt of electrical power going to the speaker from one meter away.

Stereo speakers give up a tremendous amount of efficiency in order to have a flatter, more even frequency response. A typical stereo speaker can have efficiencies in the range of 84-88dB/1 Watt/1 meter. A typical guitar amp speaker

can have efficiencies in the treble boosted area of 100dB/1 Watt/1 meter, with the Blue being around 103dB — another reason why guitar amps are so frigging loud!

Decibels (dB) are a logarithmic power scale similar in concept to the Richter scale used to measure an earthquake’s power. To get 3dB more acoustical power out of a speaker, the amp has to deliver twice as many Watts. The difference between 88dB and 100dB efficiency in speakers is like your guitar amp has 15 times as many Watts as your stereo amp.

Power Handling CapabilityGuitar speakers also differ from stereo speakers in the way they respond to varying amounts of power sent their way. The goal of a stereo speaker is to exactly reproduce the electrical signal it receives — regardless of how much power is sent. If you measure a stereo speaker’s frequency response at several different volumes, the response should be the same.

Not with guitar speakers. Their response changes when the power sent to them changes, much like non-master volume amps change character when the Volume knob is adjusted. At really low amounts of power/volume (which unfortunately is how most guitar amps are played), guitar speakers just sort of lie there and add nothing to your tone.

As the amount of power sent to the speakers moves above say three or five Watts, the increasing power wakes the speakers up and they start showing their own voice, coloring your sound in a very positive way. As the power going to the speaker increases more towards the speaker’s power handling capacity, the speaker starts overdriving, which is similar in concept to clipping an amplifier (see “Chapter Fourteen—Distortion Basics”).

Different speaker makes and models add unique frequency response characteristics, individual coloration and overdrive characteristics to your tone — which is why you have so many different speaker choices available to you.

Overdriven speakers are a key component of classic ’50s, ’60s and ’70s tone. So for a more classic vintage tone, use a speaker that is rated identically to or close to the amp’s maximum Wattage.

Professional modern tones are usually obtained through a cleaner speaker that isn’t necessarily breaking up or approaching overdrive. So for more modern tones, use a speaker that is rated for a much higher Wattage than your amp can deliver. Electro Voice makes some great extremely high-powered speakers (like 300 Watts) that are very popular for jazz.

Modern metal tones are usually made with fairly high-powered speakers. A common arrangement used by a lot of metal bands is four 12" 75 Watt Celestion G12T-75 speakers for a total of 300 Watts of power handling capability.

Figure 7.1 shows the general speaker characteristics to look for when aiming for either a classic vintage or cleaner modern tone.

CLASSIC Vintage tones

CLEANER Modern tones

Lower powered Higher powered

8", 10", 12" or 15" diameter 12" diameter

One or two speakers per cabinet Four speakers per cabinet

Lighter cone (hemp) Stiffer cone (aluminum)

AINiCo magnets Ceramic magnets

Figure 7.1 Speaker Characteristics by Tone Type

Anatomy of a Guitar SpeakerSpeakers are similar to an electric motor, with two interacting magnetic fields driving them. A fixed magnetic field is produced by the speaker’s magnet.

The magnet has a hole in the center, into which a tube, similar to the inside of a toilet paper roll, is placed. The tube is called a voice coil former and is often made of paper, Nomex or Polyimide. The tube is wound with wire called the voice coil.

Awhile back, I sent such a large voltage spike to a speaker that the voice coil shot right out of its hole in the magnet,

mangling the paper speaker cone. Amazingly, the former and coil are still intact.

Figure 7.1 is a picture of the blown speaker showing the copper voice coil wire wound around the white coil former. In a healthy speaker, the voice coil and former would be down in the hole of the donut-shaped magnet and completely out of sight. Figure 7.2 shows the front of this same blown speaker.

Figure 7.2 Blown guitar speaker showing displaced copper voice coil wound on white coil former

Figure 7.3 Blown guitar speaker showing wrinkled stiff speaker cone material

The coil former is covered by a dust cap that keeps the inside of the coil former dust-free.

When electric current from your amp passes through the voice coil, the current creates a magnetic field. This magnetic field is alternately repulsed and attracted by the permanent magnetic field created by the speaker magnet. This interaction between the two magnetic fields makes the voice coil, with its former, move back and forth inside the hole of the speaker magnet.

The speaker cone, used to push and pull air, is attached to the voice coil former. The motion of the voice coil former moves the cone and transfers the energy of the coil to the stiff cone material. The cone is held in place against the metal frame, called the basket, by a flexible rubbery material called the surround, which allows the cone to move back and forth while maintaining its side to side position.

As you can imagine, the size and types of materials used for all speaker components make a huge impact on speaker tone and how much power it can handle.

The main iTems To consider When selecTing a speaker:• Magnet material

• Cone material

• Impedance

• Diameter

• Manufacturers

Magnet MaterialThe oldest magnet material used for speakers and guitar pickups is a mixture of metals (known as an alloy) called AlNiCo, which stands for Aluminum, Nickel and Cobalt. Of the traditional materials used to make magnets, AlNiCo is particularly effective — meaning not as much magnetic material is needed to get a particular magnetic field strength.

AlNiCo was the speaker magnet of choice until the Cold War got in the way. In the early 1960s, the U.S. and British governments needed cobalt to strengthen turbine blades and other highly stressed metal components, causing the price of cobalt to increase dramatically. Suddenly, the speaker industry had to find a new magnetic material.

The magnetic material of choice became ceramic, which gets its magnetic properties from iron (also called ferrite magnets). Unfortunately, to get the same magnetic field strength as an AlNiCo magnet, a ceramic magnet requires almost twice as much weight.

But more importantly, ceramic magnets create very different tones and breakup characteristics than AlNiCo magnets. As you push an AlNiCo speaker into distortion — distortion created by the speaker itself — it distorts early and produces a smoother breakup than ceramic magnets. Conversely, ceramic magnet speakers tend to stay cleaner longer, and when they do break up they have more of a bark to them.

This difference in breakup tone between AlNiCo and Ceramic magnets is more pronounced with higher Wattage speakers. For example, the ceramic-magneted 25 Watt Greenback is a very smooth speaker, while a ceramic-magneted 75 Watt G12T-75 has much more of a crunchy punch to it.

ALNICO Magnets

CERAMIC Magnets

Distorts early Stays cleaner

Smooth break up More bark

Light Heavy

More vintage tone More modern tone

Figure 7.4 AlNiCo vs Ceramic speaker magnets

In general, when you’re looking for a vintage sound, use lower powered speakers, saving higher-powered ones for more modern sounds. But if you are really looking for a vintage feel, go for an AlNiCo speaker, which will unfortunately be more expensive but worth it.

NIBsMore recently, speaker manufacturers have been using neodymium (Neo for short) magnets. These magnets are not pure neodymium, but actually contain the alloy Nd2Fe14B (where Nd is neodymium, Fe is iron and B is boron). The abbreviation NIB is often used for this material.

NIB is the most powerful permanent magnet material currently made. You may have seen those exceptionally strong curio magnets in stores — they are made from NIB. NIB is such a strong magnet that you need to handle it with caution; it can easily erase a hard or USB drive as well as the magnetic strips on your credit cards. Two of these magnets can be attracted to each other from several inches away and slam together with such force that you can find yourself in the hospital.

In speakers, NIB is absolutely amazing in weight reduction. For example, an Eminence Tonker has a ceramic magnet weighing in at 59 ounces (1.67 kg). But Eminence has recently come out with a TonkerLite that is intended to be pretty much the same speaker with a back-friendly four ounce (0.11 kg) NIB magnet.

As far as tone is concerned, NIB speakers produce an even tighter breakup than ceramics, so I wouldn’t recommend them for vintage applications. But for jazz or tight metal, they are fabulous.

Speaker Cone MaterialSpeaker cone materials are another source of tone variation. Most speakers are made with paper cones from wood fiber, but some are made from aluminum and even hemp.

One of the main concerns with speaker cones is how accurately they can keep up with the motion of the voice coil and former.

As the frequency of the signal applied to the voice coil increases above approximately four kHz, the cone’s mass and less-than-perfectly-rigid structure cause the sound produced by the speaker to begin to quickly drop off. This drop-off at high frequencies is actually quite desirable in guitar amps because it keeps the buzz out for a smoother tone, and is why you don’t see tweeters used with guitars.

Wood FiberWood fiber (paper) is the standard for both guitar and stereo speaker construction. Wood fibers are strong, but tend to be relatively short. Unfortunately, short fibers make transmitting high frequency tones from the voice coil at the center of the cone all the way to the edges a bit difficult. Nevertheless, paper speakers have been around forever so manufacturers are very good at making them and tuning them to achieve a desired behavior.

Aluminum ConesIf you look closely at your paper speaker cones, you will see a bunch of ridges that help make them stiffer. Using a material like aluminum greatly increases the stiffness of the cone, allowing the speakers to more easily produce higher frequencies. However, high end roll-off takes away the high frequencies, and is a really good thing for guitar amp speakers. So using aluminum speakers for guitar produces some pretty harsh tones.

However, aluminum speakers have been used in bass amps with wonderful effects. In general, bass guitars work great with extended high frequency response speakers, so all of the natural harmonics of the bass strings come through.

Hemp ConesHemp fiber has been used by several manufacturers as speaker cone material. Hemp is basically the outer part of the stems of the common cannabis plant and has been used for by humans for over 7,000 years for making paper, ropes, clothes and canvas (the word ‘canvas’ is actually derived from the word ‘cannabis’). The Magna Carta, most of the Gutenberg Bibles, the King James Bible, as well as the drafts the Declaration of Independence and the United States Constitution were all created using hemp paper.

Because of its long fibers, hemp is vastly stronger than any other plant fiber. And hemp paper is also much more environmentally friendly to grow, harvest and process than wood fiber.

Additionally, hemp fibers do not require the acidic baths to make them supple like tree fibers do. Acid processing causes wood paper to eventually disintegrate, so speakers with paper cones have a built in self-destruct mechanism.

The first hemp-coned guitar speakers were a little dark, making these speakers fabulous for blues and vintage tones. Some manufacturers have been applying an enzyme treatment and using other methods to soften and tune these cones with very good success.

More work needs to be done in the use of hemp for speaker cones for both stereo and guitar. The lack of a reliable supply has stymied a lot of interest in this area. But with the availability of hemp paper apparently on the increase, we will hopefully be seeing more of these types of speakers.

Speaker DiameterSpeaker sizes are classified by the nominal diameter of the cone in inches, generally 8", 10", 12" and 15".

Eight InchersEight inch speakers are generally a one trick pony and their most famous application is in the Fender Champ. Eight inchers are also very well suited to harmonica amps. Some companies make specialized amps for the harmonica that use multiple eight inch speakers.

Ten InchersTen inch speakers are usually used in pairs or sets of four. For example, a Fender Tweed Super uses two, while a Fender Tweed Bassman and Blackface Super Reverb each use four. Ten inch speakers don’t offer the bass that larger speakers do, but using them in sets of two or four does add bass back into the sound.

Because of the added bass and overall fatness, using two or more speakers in a cabinet can sound markedly better

than using one. Unfortunately, size and weight usually limit combo amps to just one speaker. If you really want a combo with two speakers, but don’t want the weight of two twelves, two 10 inchers may be what you’re looking for.

Twelve InchersTwelve inch speakers are the size most widely used in guitar amp speaker cabinets. Twelve inch speakers offer the bass that ten inch speakers lack while providing a real punch. Twelve inchers also offer a lot more variety tone-wise because there are so many models to choose from.

The ubiquitous 4x12 cabinets have four 12" speakers and produce extraordinarily great sounds when you really drive them.

� WARNINGAlways wear earplugs when driving four 12" speakers.

If you have never had the honor of putting a cranked non-master volume 100 Watt amplifier through one or more 4x12 cabinets, you need to go do this right now. You need a really big room and you won’t be able to stand anywhere near the amp, but it is worth the hassle — otherwise, you are missing out on a key experience in life. But don’t spend too much time in front of this setup, and wear earplugs.

Fifteen InchersFifteen inch speakers are not seen very much these days. Fender used the Jensen AlNiCo 15" P15N in their Tweed Pro, and a Jensen C15P in the Blackface Pro Reverb. Both of these amps had open backed cabinets.

The white (Blonde) Showman 2x15 used JBL D-130F or JBL D-140F 15" speakers in a closed-back cabinet. The ability of the Showman cabinets to project sound all the way to the back of the room is legendary.

Misconceptions about 15" speakers are common. They are often thought to be dark and muddy and probably more suited to a bass amp — which is absolutely not the case. The sound of the Jensen 15" P15N is very balanced throughout the frequency range and not the least bit dark. In fact, I would say for vintage-style tones, the P15N in an open back cabinet is one of the best speakers I have ever heard.

Speaker ManufacturersCelestionCelestion speakers used to be produced exclusively in England by the Celestion Company. Celestion speakers are very much associated with Marshall and Vox amps; a large part of the distinctiveness of these British amps is their speakers. Throughout the years, Celestion liked to tweak the design with new production runs, so the same model may sound different from one year to the next. Many vintage Celestions are still around; they are fun to swap out to hear the different tones available from each individual speaker.

These days, Celestion is owned by a Chinese company that makes the majority of its speakers in China, although some are still made in England, notably the Blue and the Heritage series. To my ear, the Chinese speakers are not the same as the British speakers, and the British made speaker pricing reflects this quality difference.

G12H30The Celestion G12H30 is an articulate speaker rated at 30 Watts. This speaker, the standard in Marshall cabinets from the late ’60s through the ’70s, was used by everyone from Hendrix to AC/DC. Celestion now offers quite a few variations on the G12H30 theme, with the Heritage being their best offering.

I really like the G12H30 because of its punchy bass and midrange that is in-your-face without being honky. The G12H30 is equally at home in both open back and closed-back cabinets.

GreenbackThe Celestion Greenback (aka G12M25) is rated at 25 Watts and was used in older Marshall cabinets. Although Greenbacks are less efficient than G12H30s (97dB instead of 100dB/1Watt/1 meter), Greenbacks offer a less pronounced treble bump and produce an extraordinarily smooth overdriven sound à la the Allman Brothers. In my opinion, the Greenback is definitely more suited to closed-back cabinets but has been used in open back cabinets, especially when mixing different speakers in one cabinet for a fuller sound.

The BlueThe Celestion Blue is an exceptional speaker rated at 15 Watts (but in my experience easily handles around 22). The AlNiCo Blue offers a particularly chimey high end and is used in Vox AC30s (the Beatles, Queen, U2, Tom Petty). The Blue is actually an extremely old design dating back to the early 1940s; like the equally old Jensen P12N, it offers a special something in its overdrive characteristics.

Manufacturers are constantly attempting to make a higher powered Blue, but no one has succeeded. I’m not sure anyone ever will. I like the Blue in an open-back cabinet, but I’ve also heard some very old Marshall 4x12 closed-back cabinets with four Blues that sound amazing.

One thing to keep in mind with all speakers, but especially the Blue, is that when you first install a new one, it will be extremely bright and raspy. Until they are broken in after about 40 hours of use, all speakers, but especially the Blue, really give you that ice-pick-in-the-forehead tone.

The Vintage 30The Celestion Vintage 30 is an extremely popular speaker used by many amp makers. The V30 is actually a 70 Watt speaker with the treble boost occurring a little lower than other Celestions. In the hands of the right player (e.g. Sonny Landreth) an overdriven V30 can produce very cool overtones. While the V30 can be honky in an open-back cabinet, it sounds great in a closed-back cab.

In addition to the V30, Celestion makes a number of higher powered that are more applicable to modern tones. Of these more modern speakers, the G12T-75 is very much a tonal standard.

JensenJensen was an original, primary speaker supplier to Fender, so a lot of the Fender sound can be attributed to these speakers. Vintage Jensens are made with AlNiCo magnets and are very much associated with the Fender Tweed sound. Blackface Fenders use ceramic Jensens which add to the cleaner, tighter and brighter sound of these amps.

Jensen stopped making guitar speakers in the late 1960s. Thankfully, starting in the 1990s, Italian manufacturer SICA Altoparlanti started making very good reissues. If your newer Fender amp did not come with a Jensen, try to pick up an SICA-made Jensen.

The P8R, P10R, the P12N and P15N AlNiCo speakers from the Jensen Vintage series, as well as the ceramic C12N are great choices for many different amps, not just Fenders.

If you want an AlNiCo speaker that has the vintage vibe, but with a bass response that stays tight (as opposed to the Blue), and is not quite so in-your-face as a Blue, the P12N is an excellent choice. In addition to being a classic vintage style speaker, the P12N works great for modern, heavy tones because the bass holds together and the top end is smoother than a lot of ceramic speakers. Since they are AlNiCo, the P12Ns are a little pricey (don’t bother paying for the extra bell-end cap unless you are a real neat freak), but I highly suggest experimenting with this speaker either alone or in combination with other speakers.

Eminence Eminence is an American speaker manufacturer producing speakers in Eminence, Kentucky. Although it has been making speakers since 1966, Eminence has never earned the mojo that Jensen and Celestion have.

However, with the introduction of the Patriot and Red Coat series (meant to emulate Jensens and Celestions, respectively), Eminence has really come into its own as a quality speaker supplier. Eminence now makes over 10,000 speakers a day and is a wonderful example of American manufacturing at its best.

I am particularly enamored with the Governor speaker. Eminence bills this speaker as being something akin to a Celestion Vintage 30, but to my ear the Governor sounds like a high-powered (75 Watt) Celestion G12H30. I can’t say enough good things about the Governor. It is equally great in an open-back combo or a closed-back 2x12 or 4x12 cab, has a very reasonable price and is made in America!

If you want something with a little more bottom, Eminence Wizard and Tonkers are also great sounding.

The AlNiCo Red Fang is pretty decent at achieving vintage tone, but it is not a direct copy of the Blue; perhaps it’s closer to a P12N. The Eminence Private Jack is a slightly more aggressive Greenback and works great in open and closed-back cabinets.

For the price, you can definitely experiment with Eminence speakers without breaking the bank.

Ohms The geekiest thing that you will be expected to understand as a guitar player is Ohms. Ohms is simply a measure of how much a circuit resists or impedes the flow of current when voltage is applied to it… and you can use it to mold your tone.

Ohms are the ruler that we measure AC impedance and DC resistance with, and knowing your speaker cabinet’s Ohms as well as the Ohms of the individual speakers in the cabinet is important for two reasons. The first reason is the overall power delivered by the amp to the speaker cabinets and the second is the power delivered to each individual speaker.

I like to use water as an analogy when talking Ohms. Let’s say you connect a hose at the bottom of a water barrel. Voltage is the pressure at the start of the hose that is connected to the barrel’s spigot”7.1”; the pressure at the outlet or other end of the hose is zero (equivalent to ground in an electrical circuit). The rate of the current flowing through a circuit (Amps) is equivalent to the amount of water per second flowing through the hose.

Figure 7.5 Water barrel analogy for understanding Ohms

Resistance and ImpedanceThink of resistance (measured in Ohms) as “how much flow (Amps) do I get for a given amount of pressure (Volts)?” Mathematically, resistance is Volts divided by the current.

Resistance = Volts ÷ Current

A high resistance (high Ohms) circuit is like a skinny hose, while a low resistance circuit is like a fat hose.

However, the water analogy presents a slight problem in reality when you consider DC and AC voltage. DC voltage is always the same, like the voltage that a battery produces. AC voltage is constantly changing in a repeating up and down wave, like the voltage coming out of the wall socket, your guitar or your amp.

When discussing Ohms in a DC setting, we are discussing resistance. When discussing Ohms in an AC setting, we are discussing impedance. The AC impedance of a circuit is equal to the DC resistance of the circuit PLUS a resistance that is dependent on the frequency of the AC voltage.

A good analogy for DC resistance and AC impedance is to think about pushing your car up a hill. If you push the car very slowly, you are only pushing against gravity (which is always present), much like the DC resistance of a circuit. If you push your car very fast, you are not only pushing against gravity, but you also start pushing against wind resistance. The combination of gravity and wind resistance is analogous to AC impedance.

Just as wind resistance varies depending on whether the wind is blowing with you or against you, (as well as how fast you are moving), the AC impedance of a circuit varies depending on the particular frequency of the AC voltage driving the circuit.

Ohms, Practically SpeakingWhen you measure a speaker’s Ohms with a meter you are invariably measuring DC resistance (unless you have an extraordinarily complex meter). But when you look at the specs for a speaker, you will see impedance listed, not

resistance. This is because the speaker converts AC signals into sound, and really doesn’t know what to do with DC signals. Likewise, the back of your tube amp will have an impedance selector, not a resistance selector because your tube amp only puts out AC signals.

Don’t worry — a speaker’s DC resistance closely correlates with the AC impedance throughout most of the guitar’s frequency range. So if you have a speaker that does not have the impedance labelled on it, you can just measure its resistance with a meter, and the resistance reading will be slightly under the average impedance for that speaker.

To deTermine a speaker cabineT’s impedance using a volT-ohm meTer:1. Set your meter to measure resistance.

2. Plug your speaker cable into the cabinet.

3. Measure the resistance between the tip and sleeve at the other end of the speaker cable (the end that will eventually be plugged into your amp.)

4. Round up the resistance measurement to the closest impedance your amp provides.

5. Use the highest impedance selection on your amp when the measured DC resistance of your cabinet is over the highest impedance your amp has available.

Impedance and Power Delivered by an AmpThe following discussion on power and speaker Ohms applies to guitar, bass, keyboard, home stereo, car stereo or any other type of amplifier you will encounter.

In order to understand the power delivered by your amp to your speaker cabinet, we need to talk about a couple of math equations that describe the behavior of the electricity your amp is producing. Don’t get too intimidated, these are pretty straightforward equations.

Current = Voltage ÷ Impedance

This equation is known as Ohm’s Law and is just a rearrangement of the equation for resistance. Georg Ohm made many early discoveries about electricity, in particular this equation, and we now call the unit of measure for resistance and impedance Ohms. Ohm’s Law says the smaller a circuit’s impedance, the more current flows into the circuit for a given voltage.

Using the rain barrel analogy, for a given height of water in the barrel (voltage), the bigger the hose going out of the barrel (making the impedance smaller), the faster the water will come out of the barrel (more current). Conversely, the higher the level of water in the barrel, the faster the water comes out of the hose, (the height of the water in the barrel determining water pressure). This pressure is like the voltage on a circuit.

Power = Voltage × Current

This equation is the very definition of electrical power, measured in Watts (honoring James Watt who invented the practical steam engine). In everyday terms, a 60 Watt light bulb lets ½ Amp of current through with 120 Volts applied to it. 120 Volts times ½ Amp = 60 Watts.

If we work Mr. Ohm’s equation into Mr. Watt’s, we get:

Power = Voltage2 ÷ Impedance

Looking at the power equation from a voltage and impedance point of view can be helpful for visualizing some of the upcoming concepts. So in practical terms, using the 60 Watt light bulb, 120Volts ÷ (½ Amp) = 240 Ohms; and using the power equation, (120Volts × 120Volts ÷ 240 Ohms) = 60 Watts.

On an historical note, the real name for Amps (the measure of current flow) is Amperes, named for André-Marie Ampère who, like Georg Ohm, was an important pioneer in understanding electricity. Ampère is considered the father of electric motors. Likewise, Volts are named for Alessandro Volta who invented the battery. And while we are at it, hertz are named for Heinrich Hertz, who was a physicist working in electromagnetism.

Okay, that’s the math and history. Now let’s take a look at how amplifiers work in the real world.

Transistor Amps & OhmsBack to the water barrel analogy, imagine a transistor amp as having an incoming water pipe at the top of the barrel that is infinitely large (or has zero impedance). In this case, no matter how big the hose coming out of the barrel is

(how small the Ohms of the speaker gets), the height of the water in the barrel (the voltage being produced by the amp) remains the same.

Looking at the last power equation:

Power = Voltage2 ÷ Impedance

We see that the smaller the impedance gets, the more power the amp produces — assuming that the voltage doesn’t change as the power increases, which is exactly what happens in transistor amps.

So in a transistor amp, if you want more power, use a lower impedance speaker(s). The lower the impedance, the more current the amp will deliver. Because the voltage remains the same regardless of current delivered, the amp will deliver more power to the speakers as the current (Amps) increases.

However, if you look at the specs on the back of a transistor amp, you will usually find a to use something like “4 Ohms Minimum.” If you connect speakers to the amp in any way that causes the amp to see less than four Ohms (or whatever Ohm limit your amp has), you will be exceeding the amp’s ability to deliver current. Exceeding the amp’s ability to deliver current will pop a fuse (fuses pop when too much current runs through them).

0 WARNINGNever go below a transistor amp’s minimum Ohm rating or you will pop a fuse.

Getting lower power from your transistor amp is a great way to check out transistor power amp distortion at low volumes. To lower the power produced by a transistor amp, use the highest impedance arrangement your cab can deliver.

Tube Amps & OhmsWhile tubes are vastly superior to transistors for creating good tone, tubes are also different in the way they deliver power to the speaker(s).

Tube amps differ fundamentally from transistor amps when you turn up the volume. As the volume goes up and more current is drawn from the power amp, the voltage the power amp produces does not stay constant (as it does with transistor amps). As more current is drawn from the power amp, the voltage produced by the power amp actually drops.

Power = Voltage × Current

As this power equation shows, if the voltage starts dropping as the current starts rising, determining exactly at what point the amp produces maximum power is a bit tricky. You can’t just plug in the lowest impedance speaker possible because the increased current drawn by the speaker will cause the amp’s output voltage to drop.

With tube amps, we cannot assume that the pipe coming into the top of the barrel is as large as it is with a transistor amp. The pipe coming in has a smaller downspout. Because of the way tube amps work, as water is more quickly drawn out of the bottom of the barrel, the level of the water in the barrel starts to drop. Less pressure pushes the water out and it comes out less quickly.

In electrical terms, a tube amp’s internal impedance is not zero as it is with a transistor amp. Ohm’s Law shows that a tube amp’s internal impedance interacts with the current produced by the amp. This interaction creates a voltage across the internal impedance and therefore a power dissipated or used up by the internal impedance. The voltage across the internal impedance takes away from the overall voltage produced by the amp, so the voltage going to the speakers is less. Said another way, not all of the power the amp is producing gets to the speakers because some power is lost in the amp itself.

Power to speaker = Power made by amp – Power dissipated by internal impedance

The easy solution? While it sounds like figuring out how to get the maximum power from a tube amp is complicated, luckily an easy solution exists.

To geT The maximum poWer from a Tube amp:1. Make the impedance of the speaker cabinet equal to the internal impedance of the amplifier.

Most tube amps offer multiple outputs so that you can use four, eight or 16 Ohm speaker cabinets. But the amp’s internal impedance is not actually four, eight or 16 Ohms. Instead, the output transformer converts the amp’s internal impedance to these convenient impedance levels. However, the output transformer cannot convert the

amps’s internal impedance to zero and make your tube amp behave like a transistor amp.

When the output impedance of your amp matches the impedance of your speakers, equal amounts of power are dissipated by the amp and the speaker.

The power dissipated in the amp becomes heat in the power tubes and the output transformer. The power sent to your speakers becomes acoustical power delivered to the room as well as heat in the voice coil. Tubes amps are designed to handle dissipating half of the maximum power they produce within the amp, but they are not designed to dissipate all of it.

When running your amp wide open (with all master volumes all the way up) so it’s producing maximum power, matching the speaker impedance with the amp’s impedance is very important. If you don’t match the impedances, MORE than half of the power generated by the amp is dissipated in the amp, and you will be in danger of overheating your tubes and/or your output transformer. They are only designed to dissipate half the power the amp is capable of producing.

0 WARNINGPlaying your tube amp at full power with improperly matched speaker impedances will cause the output transformer and tubes to overheat and possibly catch on fire.

If you run your tube amp with no speaker at all (infinite impedance), the tubes and output transformer will need to absorb all of the amp’s power — a situation that will definitely blow something.

Additionally, having no speaker connected to a tube amp can cause spikes and ringing in the output waveform. The rather complex impedance of a speaker acts like a shock absorber, preventing the spikes and ringing from occurring.

0 WARNINGAlways run your tube amp with a speaker or some other load plugged into the speaker output. Playing your tube amp with no speaker will cause spikes and ringing that will eventually blow your amp.

The spiking and ringing can be thought of as a hammer hitting the output transformer at the peak of each wave, making the transformer ring like a bell. The start of each ring is a large spike of voltage. These voltage spikes can be high enough to break through the insulation on the transformer’s wire windings, and short your transformer — causing some pretty intense fireworks and doing some serious damage to your amp.

0 WARNINGDummy loads/attenuators can also cause voltage spikes on the output transformer. Voltage spikes will fry the output transformer as if the amp had no load — even when the impedances are all correct. For this reason, many manufacturers will void the warranty when you use a dummy load/attenuator.

Chapter Seven Footnotes

7.1 The pressure at the start of the hose is directly dependent on the height of the water in the water barrel.

I got addicted to playing the guitar at a young age from hearing those special musicians that can make you grin upon hearing the way they phrase their lines with a rhythmic and emotional vibe. The desire to be that type of player drives me to keep practicing, observing, learning, reading, and, unfortunately, always obtaining and experimenting with new gear!

Stuart VesselsV-Groove

www.v-groove.net

Chapter Eight—Cabinets

Just as guitar amp speakers are very different from stereo speakers, guitar speaker cabinets are very different from stereo speaker cabinets.

With stereo speaker cabinets, the optimal material is concrete. I’ve seen several concrete bump-out additions to houses that are built-in speaker cabinets. Google concrete speaker cabinets and you’ll find sites for portable cabs as well as pictures and designs for building concrete cabs into a building’s foundation.

The goal of a stereo speaker cabinet is to provide the volume of air needed for the speaker design to function, while being as stiff as possible with little or no resonance (movement of the cabinet) — hence the concrete. But for guitar amps, some cabinet vibration (or resonance) with the sound coming out of the speaker is often highly desirable.

In addition, while stereo speaker cabinets are always closed-back (the bass response would be extremely uneven otherwise), open-back combo cabinets are the most popular guitar cabinet.

Historically, Fender used only pine for combos and cabinets, covered by some protective material such as luggage Tweed or tolex (similar to the vinyl roof material used in cars in the ‘60s and ‘70s). The reason for pine was cost, but as with many of Fender’s choices over the years, it turned out that pine was perfect for guitar amps. Because of its light weight, pine resonates beautifully.

A good speaker cabinet is like an acoustic guitar body. So it makes sense that removing the protective tolex covering on pine cabinets makes them sound even more effervescent and airy. The only downside to naked pine cabinets is that they are easily dented and scratched, a small price to pay for excellent tone.

While eastern white pine (Pinus strobus) is a wonderful cabinet wood, any lightweight wood is a good choice, especially spruce or canary. Some boutique builders get really tweaky about the pine and use hundred-year-old boards. Aged wood is harder to work with and can be very brittle, and the tonal gains are minimal at best.

For the DIY crowd, please don’t use solid pine boards the width of your cabinet. Solid wide boards will cup and split over time. Build up to the width you need using 3" to 4" width boards to avoid the internal stresses that develop in wide boards over time.

For a nice naked finish, two coats of high gloss polyurethane followed by a medium gloss top coat are all you need. You could use more coats of polyurethane, but you would soon defeat the purpose of not using tolex. If you are going to make a wood cabinet with tolex or Tweed, seal the wood inside and out with at least one coat of polyurethane.

When it comes to 4x12 cabinets, 19mm Baltic Birch plywood is de rigueur. Baltic Birch ply is a much higher grade of plywood than you see at the hardware store because it has virtually no voids (blank spaces) in the material. If you are going to use plywood, use Baltic Birch.

Baltic Birch ply thickness is measured in millimeters, with 19mm being just a hair shy of ¾". You can use a thinner plywood, something closer to ½", or a lighter plywood, such a mahogany, to get a more resonant tone.

While I completely agree that a Baltic Birch cabinet covered in tolex is an extremely durable, rattle free material, ¾" solid pine with no tolex sounds significantly more open and alive. Using pine and covering it with tolex is a better compromise between durability and resonance than using plywood is.

Open vs. Closed-Back CabinetsGenerally speaking, closed-back cabinets, such as the venerable 4x12, offer much more bass than open-back cabinets, but are more laser beamy. Keep this in mind when you are setting up on stage; the people directly in the line of fire from your 4x12 are going to have a very different experience than people off to the sides.

To control this phenomenon, Stevie Ray Vaughan used Plexiglas shields in front of his amps. Shields also let you turn up the volume much louder to get the tone you want without causing problems with your vocal mics and band mates.

Another difference with closed-back cabinets is that the speakers can generally be hit with more power without causing them to blow. I attribute this behavior to the dampening, like a shock absorber, that the air in the cabinet provides. I still wouldn’t put 50 Watts through a single Blue in a closed-back cabinet, but you could definitely get away with 25 Watts.

A cool thing to do with 4x12 cabinets is to internally divide them into two 2x12 cabinets by placing a little shelf between the top and bottom pairs of speakers. Another cool innovation to use together with the shelf is to create removable back panels on the top and bottom parts so you can run the cabinet all closed-back, all open-back, or half open and half closed. Removable panels make for a very versatile cabinet that actually allows you to tune the cabinet’s bass response for the room.

Getting the Most Bass from Your CabThe placement of your speaker relative to room corners and the floor has a lot to do with the bass response you get from the speaker. Placing a 2x12 horizontally on the floor will give you a lot more bass than standing it vertically on one end with a speaker in the air. Similarly, moving your cabinet toward a wall or a corner also increases bass.

Speaker ClothMost guitar amp cabinets do not use sonically transparent cloth like you see on stereo speakers. Traditionally, the cloth used for guitar amp cabinets causes a bit of high frequency roll off, ranging from a mild roll-off in the cloth used in Blackface Fenders, to a quite large roll-off in the basket weave used in older Marshall cabs. A lot of Marshall amps can be a little piercing on the high end, so the basket weave is just the ticket to mellow out the sound — plus it just looks so cool.

While my lack of practice hasn’t made up for my lack of talent, every once in awhile, I come up with something, or learn something, that sounds pretty cool, and the fun in that moment is why I pick up my guitar. No objective other than to have a little fun.

Todd Z.

Chapter Nine—Power Tubes

Putting different power tubes in your amp, especially when you are planning on pushing the amp into power amp distortion, can have a huge effect on your tone. You can make an amp go from pretty gainy and crunchy, to smoother and middy, to virtually impossible to distort by simply changing power tubes from EL34s to 6L6s to KT88s/6550s, respectively.

Octal Power TubesocTal poWer Tubes come in four basic Types:

• triode

• tetrode

• pentode

• kinkless tetrode

See “Chapter Fifteen—Tube Basics” for a detailed discussion on how each tube type works.

True pentodes (EL34s and EL84s) have the widest frequency response, both lows and highs, as well as significantly higher gain than kinkless tetrodes/beam pentodes (all other power tubes used in guitar amps) do.

Any amplifier with a wide enough bias adjustment allows you to run EL34s, 6L6s, 6550s, and any of the KT tubes (check with your amp’s manufacturer to determine what tubes your amp can run). However, an amp that allows you to switch between two different pairs of power tubes on the fly is unbeatable for comparing tube types.

The Maven Peal Ganesha and RG88 offer this feature, so I’ve had a lot time to A/B various tube types while all other parts of the equipment remain exactly the same.

The variation in sound between different tube types is really quite remarkable, especially when you can push the power amp into distortion without blowing yourself out of the room (lucky for me, the Ganesha and RG88 do that, too).

So what have I discovered? 6L6s sound mid rangy, lack highs and lows and have significantly less gain than EL34s. You may think I am crazy, and in fact a leading guitar magazine once published an article stating just the opposite. The problem was that the author’s experiment involved demoing the two different sets of tubes through two different amps using two different speakers.

The author used a Blackface Fender with 6L6s and Jensen Ceramic speakers, and a Marshall with EL34s and Celestion speakers. Fender pointedly boosts the crap out of the treble, so using 6L6s sounds bright and chimey, while Marshall adds a pronounced midrange and doesn’t need to boost the high end so much (the EL34s are doing it themselves). Jensen speakers are also a lot brighter than the Celestions. So, while on the whole a Fender amp is generally brighter than a Marshall amp, the differences have much more to do with the circuits and the speakers than with the power tubes.

The differences in a pair of 6L6s and a pair of EL34s in the same amp running into the same speaker are quite dramatic. Over the years I’ve had the pleasure of attending many amp fests, and one event in particular comes to mind.

When I arrived, the Ganesha had already arrived packed with two pairs of EL34s. I swapped out one pair, put in two 6L6s and biased for the main event (the Ganesha also allows you to bias quickly from the back panel).

Thankfully, a professional guitarist was hired to play the demos, so no one had to embarrass himself. When the pro

started getting ready to play the Ganesha, I switched from EL34s to 6L6s by flipping the Tubes 1&4 and Tubes 2&3 switch.

He looked at me in horror and told me to switch it back. He thought the 6L6s were faulty. Imagine his surprise when I explained that it was only his perception that the 6L6s were faulty because he expected them to sound similar to EL34s. We put the 6L6s in another amp just to make sure they were good, and he was sold.

In the tone spectrum between 6L6s offering lower gain, mid rangy frequency response and a smooth distortion, to EL34s offering higher gain, wider frequency response (more highs and lows) and a more crunchy distortion, here’s where each tube type falls.

Lowest Gain

Highest Gain

6550 KT88 6L6 KT66 KT77 EL34

Figure 9.1 Octal Power Tube Gain Spectrum

KT88s and 6550s are both much higher-powered tubes and have tremendous amounts of headroom. The frequency response of these higher-powered tubes is more extended, but not as extended as EL34s, and the distortion is not as crunchy as EL34s. To me, KT88s are better than the 6550s when you need to pummel your speakers.

For awhile in the ’70s, Marshall’s American distributor used 6550s. In fact, Marshall itself used 6L6s in the ’90s when tube supplies got tight. In either case, have your tech change whatever tubes you currently have to EL34s to get a more Marshall sound.

Marshall also made the 200 Watt Marshall Major using KT88s, as made famous by Jimmy Page in the Song Remains the Same tour. Please, never use anything but KT88s in that amp.

EL84sEL84s have smaller bases than octal tubes (with the same base as 9 pin preamp tubes), so if your amp takes these tubes, you don’t have a choice. That said, EL84s are my personal favorite. These little babies are capable of many things (and I bet you thought that they were chimey and lacking bass because of the Vox AC30 — the tone of the AC30 is due to a number of variables, not just the power tubes).

While EL84s have an extended high end response like EL34s, in the right amp they also have tremendous bass response. The Maven Peal Zeeta came stock with two EL84s and a Celestion Blue speaker. The Blue is rated at 15 Watts, but the Zeeta runs the EL84s hot, getting about 22 Watts distorted with no problem. I have a friend who owns a boatload of seven string guitars. When he thumps on that low string with the Zeeta, the speaker cone just about flies across the room (and that is with the Wattage knob turned down).

While the Blues are not equipped to handle those low notes, the EL84s sure are.

Power Tube LifeThe unfortunate reality with all power tubes is that they wear out. A working musician will go through a set of power tubes in six months or less.

signs ThaT your Tubes are on Their Way ouT include: • Excessive blue haze in the tube when on.

• The amp is too saggy — it feels funny like it’s half a step behind you.

• The high end of the amp is just not there.

• The low end of the amp is really not there either.

• The amp begins getting strangely noisy, particularly when you are playing a single note — aka power tube microphonics.

In the end, tubes are just light bulbs (the heater is a light bulb and the cathode runs at about the same temperature), surrounded by a bunch of grids and an anode/plate, so you can’t expect them to last forever. Preamp tubes, however, should last for decades since they aren’t asked to make much power and they operate at a much lower temperature.

Tube ManufacturersVery old tubes made by the original manufacturer that have not yet been used are called NOS for New Old Stock. I call new tubes made with the old names ONNS for Old Name New Stock.

NOS tubes can get really expensive and many are actually quite used or even counterfeit. Please be careful when buying NOS tubes. Always get them from a reputable source like Antique Electronic Supply or one of the techs in “Chapter Four—Great Recommendations”

I personally don’t think NOS power tubes are worth the money because they wear out quickly. On the other hand, NOS preamp tubes often last for decades, and can do wonders for your amp making it generally smoother (see “Chapter Ten—Preamp Tubes” for more info).

Never ship an amp with NOS tubes installed; you’re just asking for trouble. Ship these gems separately in lots of bubble wrap.

TAD, Ruby Tubes and Groove TubesFew companies make tubes today. The ones that do are in Russia, Eastern Europe and China. For my part, I don’t care for Chinese tubes. While they are inexpensive, I find them to be inconsistent and not up to the level of performance of European tubes. That said, some Chinese made tubes are worth noting, in particular the TAD (Tube Amp Doctor), Ruby Tubes and the Groove Tubes KT66HP.

JJ-ElectronicJJ-Electronic (formerly Tesla) in the Slovak Republic makes absolutely outstanding power tubes. I have never had problems with these tubes, even in the Ganesha which is more powerful than a vintage Marshall Plexi. I have even put JJ 6V6s in a Ganesha (with the Wattage knob down), and they survived quite well. While I don’t recommend this treatment of any 6V6, it’s nice to know JJs are that tough.

My only issue with JJ power tubes is their 6L6. This is a rugged tube and will last, but it sounds just like an EL34 to me. I’m guessing they made the 6L6s too well, and the virtual suppressor grid is ably doing its job, making the tube behave almost identically to a real pentode.

Likewise, the JJ 6V6 sounds very similar to a mini 6L6. While the 6V6 is designed to be a mini 6L6, vintage American 6V6s have a swampy sound that is just not captured in new 6V6s. But at least 6V6s are available again, so we can’t complain too much. From the late 1980s until 2005, no acceptable quality 6V6s were available, which was a real tonal drag.

The JJ E34L (a higher quality EL34) and their EL84 are second to none in sound quality and sturdiness. I also really like the KT77 for an EL34 sound that is backed off just a bit for more smoothness. The JJ KT88 is an excellent choice for high power amps, or as a tube that will stay punchy and clean right up to the ragged edge of your amp’s abilities.

SvetlanaAnother really great tube factory is Svetlana in St. Petersburg, Russia. Unfortunately, some misunderstandings have developed in North America concerning Svetlana.

The North American distributor for Svetlana was initially a company called Svetlana Electron Distributors, and they owned the Svetlana trademark in America. When the Svetlana factory in St. Petersburg discontinued its relationship with Svetlana Electron Distributors, the distributor sold the Svetlana trademark to New Sensor, a competing manufacturer/distributor headquartered in New York. (New Sensor coincidently owns the Reflector tube factory in Russia.)

Tubes made in the actual Svetlana factory are now labelled SED for Svetlana Electron Devices with the Winged C logo (C in the Russian alphabet is pronounced like an S in English). New Sensor sells tubes labelled Svetlana that are actually made in the Reflector factory. It is an unnecessarily confusing mess that should never have happened, but there it is.

In my opinion, the Winged C 6L6s and 6550s are the best current production tubes of those types. Likewise, Winged C 12AX7s are right up there with the best currently made 12AX7s available.

New SensorNew Sensor manufactures tubes at the Reflector factory in Russia under a large number of names including Sovtek, Electro-Harmonix, Tung-Sol, Mullard, Genalex, and now Svetlana.

The trade names Genalex, Mullard, and Tung-Sol are names of tube manufacturers in the hey-day (1950s-1970s) of tube making. The original products made by these companies are absolutely outstanding. Unfortunately, none of these companies has made tubes in decades.

New Sensor now owns the rights to these names and builds tubes as replicas of the originals. As far as power tubes go, the ONNS Tung-Sol 5881 and the ONNS Genalex KT66 are excellent choices.

The ONNS Tung-Sol 12AX7 tube made in the Reflector factory is one of the best available.

Tube RectifiersThe American designation for a rectifier tube generally starts with five since the heaters in these tubes usually run on five Volts. Common rectifier tubes are the GZ34/5AR4, the high power/low sag 5U4GB, and the low power/high sag 5Y3 and EZ81/6CA4.

If your amp uses a tube rectifier(s) (aka tube diodes), you should replace it/these when you replace your power tubes… or not. Older rectifier tubes can add a significant amount of sag to your amp, which you may or may not want on any given day. Keeping several different rectifier tube types (make or age) around is a cool way to tweak your amp to your taste with a simple tube switch.”9.1”

When looking for new rectifier tubes, JJs will generally give your amp the punchiest, loudest, cleanest tone. ONNS such as Tung-Sols give you the saggiest tones.

Remember, if you want your amp’s tone to be affected by the rectifier tubes, you are going to have to play pretty darn loud.

� WARNINGAlways protect your hearing by wearing earplugs when playing your amp loudly.

Chapter Nine Footnotes

9.1 Strictly speaking, you should rebias when you switch rectifier tubes, but you can usually get away without rebiasing. In the most extreme case, if you go from a really old rectifier tube to a new one, you might be pushing your power tubes too hard and will need to turn down the bias. Conversely, if you put an old rectifier in where you previously had a tight new rectifier, your amp might be biased too cold and you could get crossover distortion.

The guitar is a consistently joyous haven from everyday life. Simple yet complex, delicate or aggressive; you get back exactly what you put in — just like any good friend.

Steve Nurme

Chapter Ten—Preamp Tubes

One of the great things about tube guitar amps is that you can tweak your sound relatively easily, and one of the easiest ways to change your amp’s tone is to change the preamp tubes, which never need biasing.

You can put in different models of the tube type the amp was designed for, or in some cases, you can use a completely different tube type to radically alter the sound. For example, you can try 12AX7/ECC83 preamp tubes from different manufacturers in various positions to see how the same tube type from different manufacturers changes your tone. Or you can create even more dramatic tonal change by going from a 12AX7 to a 12AY7, 12AT7 or 12AU7.

Not all preamp tubes or circuits allow for a change in tube type. First, you need to know what tube type the amp manufacturer intended to be in there. Then you have to know what tube types will be acceptable substitutes for the stock tube. “Appendix C—Preamp Tube Types” lists acceptable preamp tubes substitutes for all 12A** preamp tubes.

As you can see from Appendix C—Preamp Tube Types” never substitute a lower-powered preamp tube into a socket that is expecting a higher-powered preamp tube, but vice versa is okay.

0 WARNINGAlways substitute preamp tubes that are rated equal to or higher than the Wattage rating for the amplifier’s stock preamp tubes.

Likewise, many high gain amps come with lower gain tubes as a conscious choice of the builder to tame the amp a bit. You should continue to use lower gain tubes in these types of amps, as adding more gain can easily cause unwanted oscillation resulting in a high pitched ringing.

To tame an amp’s gain, players often replace a 12AX7 with a 12AT7. While this switch is an effective and workable substitute, the 12AY7 is actually more electrically similar to a 12AX7, so the overall tone of the amp will be changed less and the gain will be down even more than if you sub in a 12AT7.

Unfortunately, the 12AY7 is no longer produced. However, NOS 12AY7s are readily available for a reasonable price. I highly suggest trying one or two if you have an amp that needs taming.

Be careful not to put any of the tubes in the chart (which are dual triodes in one package) into a socket meant for a preamp pentode, usually an EF86. The EF86, (and its variants EF806 and 6267) are not compatible with the 12A** tubes we are discussing and you will smoke your amp if you mix up these tube types. Some of the amps that use an EF86 include early Voxes and their clones, especially the AC15, VHT/Fryette, Matchless, Bad Cat, Dr. Z and 65 Amps.

0 WARNINGDo not use any tubes in the chart in a socket meant for a preamp pentode. The EF86, EF806 and 6267 are not compatible with 12A** tubes and will blow your amp.

As the preamp tube chart suggests, you can substitute a higher-powered tube for a low powered stock tube, but not vice versa.

For example, a 200 Watt Marshall Major uses a 12AU7 in the power amp. While you probably can get away with using a 12AT7 in that socket, you definitely cannot use a 12AX7 or 12AY7. On the other hand, Blackface and Silverface Fenders use a 12AT7 for the phase inverter, and you could easily use a 12AU7 in that position to cut down the power amp gain; but using a 12AX7 in the phase inverter to increase the power amp gain is pushing it, since a 12AX7 is a lower-powered tube (see “Appendix C—Preamp Tube Types”).

In addition to substituting a new tube type when trying to calm an overly gainy amp, you can use a lower gain tube of the same type. For example, if your amp comes with 12AX7s, you can substitute a lower gain JJ ECC83 (European designation for a 12AX7).

Because so many variations on a 12AX7 exist, and because they change so frequently, your tube supplier can best steer you in the right direction regarding the relative amounts of gain of various 12AX7s. I suggest an SED, ONNS (Old Name New Stock) Tung-Sol or JJ ECC83S as a high gain 12AX7; and the JJ ECC83 as a low gain 12AX7.

When replacing preamp tube types, always have a plan of attack. Most amps label the preamp tubes V1, V2, V3 etc., with V1 being closest to the input jack and the highest numbered tube being farthest from the input jack. Check your amp to make sure you know which preamp tube is which.

In most amps, V1 will be used in the first stage of gain. The highest numbered preamp tube will usually be used as the phase inverter. The second to the highest numbered tube will usually be the last preamp gain stage and often the tone stack driver.

All the preamp tubes between the first gain stage tube and the last gain stage tube will usually be used for additional gain stages in higher gain channels, with the exception of amps that have tremolo or reverb circuits which use their own tubes. So for example, in an RG88 (which has no tremolo or reverb), V1 is the closest tube to the input jack and is the first gain stage for both the clean and high gain channels; V2 is used exclusively for the high gain channel; V3 is the last gain stage for both channels and drives the tone stacks, with V4 as the phase inverter tube.

If you are trying to cut down the gain of the first channel of the RG88, you can replace either V1 or V3 with a lower gain tube. Note that changing V1 or V3 will also decrease the gain of the second channel. Decreasing the gain of a high gain channel via tube replacement is still going to leave you with pretty high gain, so don’t sweat that. If you just want to cut the gain on the second channel on the RG88, replace V2 only.

Generally speaking, a good plan of attack when you need to cut down the gain of your amp is to start with V1. If you are not getting the results you need, then start cutting the gain down via V1 and V2. If you find yourself with 12AU7s throughout your preamp, and you still want to cut the gain further, try going after the phase inverter.

NOS Preamp TubesIn my amps, I generally like NOS Mullard ECC83s (12AX7) in all positions except the phase inverter tube (which is usually the farthest preamp tube from the Input jack). For the phase inverter, I like a NOS Telefunken ECC83/12AX7.

Never ship an amp with NOS tubes installed; you’re just asking for trouble. Ship these gems separately in lots of bubble wrap.

My guitar picks me up, and carries me away. The journey is sometimes short and simple, other times longer and harder, but always opens a door to another world: The music rises and surrounds me, and the cares of the every day drop behind.

David Brittenham

Chapter Eleven—Cords and Cables

Like tubes, external cables are a component that can have a big impact on your tone. Figure 11.1 on the next page lists the three types of cables you will need to play your amp:

• Guitar cords (aka) preamp level signal cables

• Speaker cable

• Power cords

Microphone cable is also included in the list in Figure 11.1 for comparison even though you only need a mic cable if you’re using a mic.

Guitar CableThe job of any coaxial cable, including guitar cables, is to transfer an extremely low power signal from one device to another with minimal signal loss, signal distortion and noise introduction.

CABLE type

RESISTANCE/ iMpedanceof connectedcircuitry

CURRENT carried by Wire (typical)

VOLTAGE carried by Wire (typical)

Guitar 10,000 to 1,000,000 Ohms

.1 to 100 micro Amps (1/1,000,000 of an Amp)

.1 to 100 milliVolts (1/1000 a Volt)

Microphone 100 to 600 Ohms 1 to 20 micro Amps

.1 to 10 milliVolts

Speaker 4 to 32 Ohms 1 to 20 Amps 1 to 40 Volts

Power 10 to 20 Ohms 1 to 10 Amps 120 to 240 Volts

Figure 11.1 Circuit Impedance & Typical Current and Voltage by Cable Type

To eliminate noise, guitar cords are constructed with a shield that wraps around the entire cable and is then connected to ground. Any noise coming from outside the cable should be intercepted by the shield and shunted harmlessly away to ground.

Figure 11.2 Guitar cable innards

Inside the shield is an insulating material, and at the very center is the hot or signal conductor — usually a set of stranded wires with an overall thickness (or gage) on the small side to accommodate the low current traveling through the cable.

Guitar cords differ widely in shielding effectiveness and the capacitance of insulating material. Two signal conductors separated by an insulator form a capacitor.

Capacitors and CapacitanceTo really understand cords and cables, you should understand what capacitance is, and the definition differs for DC versus AC current.

With DC voltage, capacitance is the measure of how much electrical charge a circuit will hold for a given voltage.

In AC terms, capacitance blocks lower frequencies and lets higher frequencies pass. The higher the capacitance, the lower the frequency of AC that can pass through the circuit.

Your guitar cables carry AC from your guitar to your amp. If there is a lot of capacitance between the center conductor and the cable shield, the high frequencies in your guitar signal will pass through the capacitor that is your cable and be shunted to the grounded shield and lost. The more capacitance in your cable, the lower the frequency at which this loss starts to occur. So you want the capacitance of your cables to be low enough so that only frequencies that are too high to hear are lost to ground.

If you have a crappy shield, noise will get into the hot, inner conductor and then into your amp. If the insulating material does not hold the hot conductor firmly in place, you can get very strange tonal issues (essentially microphonics), especially with higher level signals when using say, an effects pedal.

Low quality insulating material will also cause a lot of capacitance, which will also cause tone problems because you will be losing some of your high end.

When using a guitar cable, you are essentially adding a capacitor connected from the signal conductor to ground (the shield). A capacitor connected to ground is what makes the tone control on your guitar roll-off high frequencies when you turn it down. So it makes sense that cables always roll-off some high end.

With a high quality cable, the high end roll-off occurs higher than the highest frequency in the guitar signal so roll-off isn’t a problem. If you’re using an average cable, you will experience some roll-off depending on the length of the cable.

The longer the guitar cable, the bigger the effective capacitor. In fact, cable capacitance is measured in pF/Foot (that

is, picofarads per foot). So always keep your guitar cables as short as possible — except, of course, for when you want to use the high end roll-off to your advantage.

For example, Warren Haynes has a particular wah-wah pedal that is a little bright. So his tech runs an extra long cable to the pedal, with another extra long cable back to the amp, effectively creating a high end-cut tone control that helps tame the pedal.

Besides rolling off high frequencies, guitar cables can cause a problem that is often described by musicians as smearing the sound. Engineers call this Phase Shift/ Group Delay, which brings up an important engineering/musical concept. Allow me to digress for just a moment.

Harmonic Content of a Sound WaveYou can look at a sound wave in one of two ways, the first involving the harmonic content or frequency domain.

Imagine a series of sine waves (those very smooth waves you see on oscilloscopes in the movies) stacked on top of each other. The lowest frequency sine wave is called the fundamental frequency, and all sine waves above it are frequencies that are whole-number (2, 3, 4, etc.) multiples of the fundamental frequency. These higher frequency sine waves are called harmonics of the fundamental.

The first wave above the fundamental is called the second harmonic (2x the frequency of the fundamental) and represents an octave above the fundamental. The third harmonic is an octave plus a fifth above the fundamental; the fourth harmonic is two octaves above the fundamental.

As we go up in frequency, we get more complex harmonics: the fifth harmonic is two octaves and a major third above the fundamental; the sixth harmonic is two octaves and a fifth above the fundamental; the seventh harmonic is two octaves and a minor seventh above the fundamental; and the eighth harmonic is three octaves above the fundamental. Figure 11.3 shows an example of a fundamental and its first few odd harmonics as separate waveforms.

Figure 11.3 Sine Waves Showing the Fundamental and a Series of Odd Harmonics

When you pluck a guitar string, you are creating the fundamental along with the harmonics. Your individual tone is represented by the particular mixture of sizes, or loudness, of harmonics.

When you run an electrical signal through a low pass filter (which is essentially what the resistance of your guitar pickups plus the capacitance of your guitar cable is), higher harmonics are basically turned down in volume while lower harmonics are left alone. This condition is called rolling off the high end, and is a good example of the tonal changes that your guitar cable, or low pass filter (like your guitar’s Tone knob), can produce.

good guiTar cable affecTs only Those frequencies ThaT are:• So high they are not in the guitar signal

• Filtered to a large degree by other parts of your equipment

• Beyond auditory range

A bad cable will get right in the thick of your tone and mess with your high end volume.

Time Domain of a Sound WaveThe second way to understand a sound wave is to look at it in the time domain. That is to say, what does the wave actually look like on an oscilloscope?

On an oscilloscope, we don’t see a grouping of the individual sine waves; instead we see the result of these waves melded together into one wave. Figure 11.4 shows the result of adding all of the waves in Figure 11.3 together.

Figure 11.4 Fundamental with Odd Harmonics Combined

A signal in the time domain shows a definite change before and after going through a low pass filter — the overall shape of the wave is smoother.

Now, if we had a whole bunch of identical low pass filters, and were clever enough to be able to put each harmonic through its own filter, we’d be able to see some interesting stuff going on. Looking at each filtered harmonic separately on an oscilloscope, we’d see that not only are the higher harmonics smaller (quieter) after passing through the filter, the high harmonics are shifted in time relative to the fundamental — almost as if going through the filter made the high harmonics go through a time warp that made them come out a little behind the low frequency harmonics.

The time shift is referred to as phase shift or group delay, and it actually occurs. A signal that has been phase-shifted not only has higher harmonics that are potentially smaller, but the high harmonics are shifted relative to the other harmonics. Phase shift causes the shape of the overall wave form to look different on the oscilloscope than it does when no shift occurs.

Figure 11.5 shows the same fundamental and harmonics as Figure 11.3, except that the harmonics have been phase-shifted as if they had run through a cable good enough not to cut the high-end appreciably, but bad enough to cause phase shift.

Figure 11.5 Fundamental and Phase Shifted Harmonics

Phase shifting higher harmonics gives the impression that your sound has been smeared or blurred and is lacking clarity. What is most insidious about phase shift is that the effect occurs over a much wider range of frequencies than the actual lowering of volume of the high harmonics that normally occurs with a low pass filter. For example, if your low pass filter starts affecting the volume of high harmonics starting at 20kHz and up, the phase shifting will start at 10kHz and sometimes lower.

Figure 11.6 shows the result of adding the fundamental and the harmonics from Figure 11.5. The waveform in Figure 11.6 is reminiscent of the waveform in Figure 11.4, but it clearly is not the same, and your ears can definitely hear the difference.

Figure 11.6 Sum of Fundamental and Phase Shifted Harmonics

So when a guitarist tells you that his most excellent low capacitance guitar cable makes his signal clearer than his normal cables, he is likely correct; but perhaps not for the reason that everyone thinks — the reduction of high frequencies. The added clarity is more likely due to phase shifting of high frequencies, or more specifically, the lack thereof.

The bottom line with guitar cable: Look for the lowest-capacitance-per-foot cable and the shortest run of cable that you can live with. My customers and I have had excellent experiences with George L. cable.

High end roll-off and attendant phase shifting are not only caused by the guitar cable. Another culprit can be the output impedance (AC resistance) of the device driving the cable, which along with the capacitance of the cable form a low pass filter. So decreasing your guitar’s output impedance will help you achieve the same effect as using a really high end cable.

How do you control your guitar’s output impedance? By adjusting the Volume on your guitar. Guitars can have output impedances in the range of thousands of Ohms to tens or even hundreds of thousands of Ohms, depending on whether or not the Volume control is wide open (lower Ohms) or turned down (higher Ohms).

The increase in output impedance of your guitar, interacting with the capacitance of your cable (and your amp) is what causes the high end roll-off when you turn your guitar’s Volume knob down. If you have a great cable (specifically meaning low capacitance) and a great amp this effect won’t happen — or more technically, it will happen at such a high frequency, you won’t notice.

Electronic BufferBy comparison, a microphone’s output impedance is in the range of hundreds of Ohms, so you can run a mic cable ten times as long as a guitar cable and still get good performance. And with an electronic buffer in your guitar or stomp box, you can get the same results (depending on how good the buffer is). With a good buffer you could drive a cable 1000 feet long and it would sound the same as a 10 foot cable connected straight into your guitar.

If you have a preamp on your guitar that takes a battery (aka an active preamp), you most likely have a built in-buffer, and cable choice will not be such an issue for you. If you do not have an active preamp in your guitar and find yourself in a situation in which you have to run a really long cable, first plug your guitar (with a short cable) into a neutral-sounding buffer and then run the long cable from the buffer to wherever it needs to go.

Speaker CablesSpeaker cables are used to transfer power from the amplifier to the speakers. Transferring these large amounts of power is a fundamentally different job from what guitar cords do.

Speaker cables are not made to keep noise out like guitar cables are. Instead of a hot wire wrapped inside a grounded conductor (a coaxial cable), speaker cables have the hot wire and ground wires next to each other, like the AC power cord for a lamp. Having the two wires next to each other greatly reduces the capacitance per foot compared to a coaxial cable, but speaker cable does not have the noise-shielding properties of a guitar cable.

Fortunately, noise that gets into your speaker cables is so small compared to the large signal the cables are carrying that you really can’t hear it. In technical terms, the signal-to-noise ratio is very large, which is what you want in all of your gear.

Another big difference between speaker and guitar cables is that the amount of current flowing through speaker

wires is much higher than the current flowing through guitar cables. So the resistance of the wires and their current-carrying-capacity (aka ampacity) become major issues. (The resistance in your guitar cable wire is a fairly minor issue compared to the capacitance of the guitar cable.)

Every wire you can hope to afford comes with some amount of resistance. This wire resistance turns some of the amp’s power into heat, causing the wire to become hot and reducing the power that reaches the speaker. A wire’s ampacity is how much current (measured in Amps) the wire can carry without going over a certain temperature, often 60 or 90 degrees Celsius (which is pretty damn hot).

At first glance, you might think the lowest resistance (and highest ampacity) wire you can get is what you’ll need for great speaker wire. As short and fat as possible, made with the lowest resistance material available, usually copper — or silver if you want to get crazy.

Figure 11.7 Speaker cable innards

If short fat copper wire is what works, then why not use car battery jumper cables and put some connectors on the end? You can do that, but reality is a little more complex. As we discussed earlier in “Chapter Seven—Speakers” the difference between a wire’s DC resistance and AC impedance plays a big role.

The AC impedance of a speaker cable is equal to the DC resistance of the cable PLUS the impedance created by the capacitance and inductance of the cable. Earlier, we discussed how the coaxial arrangement of the guitar cable creates a capacitor between the hot wire and the ground shield.

In the case of speaker cables, while some capacitance between the two wires laid next to each other exists, there is also — and often more importantly — inductance between the two wires.

Any wire with current flowing through it has a magnetic field around it. When two wires are next to each other, the magnetic field produced by the current on one wire affects the current flowing in the other wire (and vice versa). With speaker cable, the end result is the creation of a virtual inductor (a coil), otherwise known as a choke, in series with the speaker cable. An inductor in series with the flow of electricity drops voltage across it, reducing the voltage transferred to the load (which in this case is the speaker).

As with the guitar cable’s capacitance, the speaker cable’s inductance will affect higher frequencies much more dramatically than lower frequencies. The result is a volume decrease in higher frequencies along with companion phase shifting, combining to blur your tone.

To minimize this effect, the cable wire diameter needs to be as small as possible, which is why using jumper cables for speaker wire is not a good idea. I once saw an engineering study in a now out-of-print audio magazine of various speaker wires, including jumper cables; it was surprising just how bad jumpers are.

So quality speaker wire actually has competing requirements: large wire for low resistance and smaller wire for lower inductance. Generally speaking, if your speaker cable is somewhere between 16GA and 12GA, and as short as possible, you will be fine.”11.1”

The bottom line: Don’t go overboard with big fat speaker wire. Better quality speaker wire tries to reach a magical balance of low resistance, low capacitance and low inductance. I have had particularly good luck with Evidence cables.

Ribbon Speaker CableIf you really want to be an audiophile about your speaker cables, the best I have ever heard as well as the best performing in engineering tests are based on ribbon cable. Ribbon cable looks flat and has a large number of small

wires insulated from each other — perhaps 12 or 20, or even more.

However, ribbon cable inside an amplifier is usually an indication that you’ve got yourself a low-quality mass-produced amp. When used to carry a bunch of different signals from one point to another, ribbon cables can lead to some serious crosstalk. Crosstalk occurs when the signal from one part of the amp is injected into another part of the amp where it doesn’t belong — and it really messes up your sound.

Ribbon cable used for speaker wire, however, carries only one signal — the amp’s output to the speaker — and crosstalk is not a possibility.

The wires in ribbon cable tend to be rather small, 22GA or less. This small size is great for speaker cable because the goal is to reduce inductance. By alternately connecting the wires from ground to hot, the bunch of little wires create one big wire, making DC resistance low, and the inductance not through the roof.

I have seen these ribbon cables used a lot as speaker wire for high end stereo systems, but you don’t see them used much for guitar amps or PA systems. Planet Waves makes a guitar amp compatible ribbon cable speaker wire that is worth looking into.

If you are going through the trouble of purchasing good speaker cable, take the time to look at the wires inside your cabinet. I have seen some atrocious excuses for hookup wire used in mass produced 4x12 cabinets. I’m surprised that the wire in some of these cabinets doesn’t glow red hot and burn out.

If your cabinet has some really thin wires, please get some 18GA or 16GA stranded hookup wire and rewire your cabinet (or have your tech do it for you). The voltage rating of the wire insulation is not an issue because you aren’t going to get more than 60 Volts out of your amp (even with a 200 Watt amp), so 100 Volts insulation is fine. If you want to go over the top, use fancy silver-plated hookup wire. Mouser Electronics is a great source.

And finally — please don’t leave your wires plugged in until the end of time. The metal on the wire connector, as well as the connector on your amp and speaker, will corrode slightly (unless they are gold), causing the connectors’ resistance to increase. Pull the connector out, wipe it off and plug it back in every so often.

Same goes for your stereo gear, your effects pedals, or anything else with mechanical connections.

Power CableThe last kind of cable guitar players need to know about is the power cable going from the wall outlet to the amp. This cable carries between one and ten Amps from the wall wires to your amp’s internal AC wiring. Its goal is to transfer the power from the wall to the amp with the absolute minimum amount of voltage drop possible.

To minimize voltage drop, the wire’s DC resistance needs to be low. Since the frequency of the electrical power going through the cable is always very low — 60Hz in North America or 50Hz everywhere else — the cable’s performance is not affected by its capacitance or inductance. These two parameters affect high frequencies far more than very low frequencies. However, resistance affects all frequencies equally, including zero frequency (or DC).

So, given the amount of current most amps draw, an 18GA wire makes a fine power cord. If you really want to get nuts or you have a big monster amp, get 12GA wire. Since the wiring in your house is 12GA, going any thicker will not have a noticeable sonic impact.

But, if you really have a need to break out the jumper cables to increase the mojo of your amp rig, the power cord is probably the right place to do it.

Some pretty far out AC power cords are available costing hundreds, even thousands, of dollars. These fancy cords usually feature hospital-grade connectors, which are certainly far better than regular connectors.

Hospital-grade connectors have solid lugs as opposed to folded ones — solid lugs are great for very sturdy ground connections. Hospital-grade cable means that only the connectors are hospital-grade; the cord itself can be pretty much any type of wire, so be sure to check this (no sense having high end connectors and low end cable). True hospital-grade connectors have a green dot on them, usually near the ground lug.

I own several hospital-grade power cords, but don’t use them often. I don’t like the humongous wire, and they’re so fancy I don’t take them out of the studio. But they are great to look at.

The only technical reason for using wires any bigger than 12GA in your power cords is if you have a dedicated circuit from your power panel to your amp room using 10GA wire — then 10GA would be called for. But even then, your amp simply does not pull that much current from the wall to make a huge difference; but every little bit helps.

Using shielded power cable can make a big difference when you are trying to reduce hum. AC power cords essentially radiate AC hum into the environment around them. Shielded power cable will keep this particular source of hum inside the wire and out of the rest of your gear.

One Last TipIf your amp offers a 240 Volt setting, here’s a suggestion you can try if you really want to get high end with your AC power.

Have your electrician run a 240 Volt line from your power panel to your amp room. Get a special 240 Volt cable to connect your amp to the wall, and run the amp on 240 Volts.

With the 240 Volt selection, all the windings on the primary (input) side of the power transformer are used, but they draw only half the current from the wall (compared to the normal North American 120 Volts). The voltage drop due to current flowing in the wall wiring and your nifty power cord will be half of what it would be if you ran your amp on 120 Volts.

Keep in mind that American parts supply houses may label wall sockets/plugs etc., as 220 Volts instead of 240 Volts — this is just an old habit that is hard to break. Rest assured that the wall voltage will be around 240 to 250 Volts.

In the spirit of using all of a transformer’s windings, thereby using a higher voltage and a lower current, you can also use a higher Ohm speaker cabinet. For example, a 16 Ohm cabinet will use all of the windings on the secondary side of the output transformer and will draw half the Amps”11.2” of a four Ohm speaker cabinet. This will cause half the voltage to drop in your cool speaker wire, making your tone twice as nice.

Chapter Eleven Footnotes

11.1 Wire thickness in North America is measured by Gage, abbreviated GA. The smaller the Gage number, the larger the wire diameter.

11.2 That’s correct — half the power. The equation is:

Current2 × Impedance = Power

when i play my guitar, the voices in my head stop…

“grateful ed” knowltonpicus maximus

www.picus.maximus.com

Chapter Twelve—A Word About Volume

Volume brings out the magic of vintage and traditional style amps, and the louder the better. Volume summons the magic in modern master volume, multichannel amps as well. For this reason, too many players develop tinnitus or lose their hearing in pursuit of that ultimate tone. I cannot say enough about the importance of wearing earplugs.

� WARNINGAlways wear earplugs when playing your guitar louder than you would comfortably listen to your television. Tinnitus is forever; the song you’re playing isn’t.

Why Higher Volume Sounds BetterAmps sound better at higher volumes for several reasons. Some have to do with the way your amp and speakers behave at higher volumes (output power) and some have to do with how your ear behaves at higher volumes. All of the reasons, however, are due to the non-linear nature of the real world.

Amp Response At Higher VolumesAmps sound better at higher volumes because the power amp is distorting. Power amp distortion is an inherently engaging and distinctive tone that works well with all types of music from jazz to heavy metal. If you rely only on preamp distortion to get your tone, you will come up short in the tone department.

To drive your power amp into distortion, you need to make the power amp produce as many Watts as possible. The problem, of course, is that if your amp is rated for anything higher than a couple of Watts, the volume will quickly start to get pretty darn loud.

In addition to the power amp distorting, as you turn up the volume your speakers go from just kind of lying there to waking up, then breaking up into a distortion that really adds to your tone, bringing out the real character of the individual speaker. Of course, all of this character is going to be very loud.

Finally, when you turn the amp up enough to begin distorting the power amp, the power supply begins to sag. A sagging power supply adds roundness to the tone and touch responsiveness to the amp that you just can’t get using any other method.

Human Ear Response to Higher VolumeYour ears do not work exactly the same at every volume any more than your amp does. At lower volumes, the frequency response of your ears is peaked in the middle and drops off at lower and higher frequencies. This non-flat response is why stereos have loudness controls. At lower volumes, the loudness control boosts the bass and treble to compensate for your ears.

As the volume goes up, your ears develop a flatter and flatter frequency response, so that at very high volumes, the bass, middle and treble frequencies are perceived by your ear and brain equally. This volume-dependent response was revealed in the pioneering work of Fletcher and Munson, and is shown in the frequency response charts they created called the Fletcher-Munson curves.

In addition to the frequency-response changes your ears exhibit as volume goes up, another phenomenon is at work — your ears actually work better at higher volumes. This strange behavior can be more easily described by analogy to your eyes in light response, which are strikingly similar to your ears in volume response.

As we all know, we see better in brighter light. However, if you think of black letters on a white page, the contrast between the white and the black remains the same whether a lot of light is shining, or just a little. But with brighter light, our eyes wake up and become more sensitive.

More light is to your eyes as higher volume is to your ears. And as with your eyes, your ears are able to hear subtle nuances in music better when the music is louder, because your ears are more sensitive at higher volumes.

Just like looking at the sun can blind you, listening to music that is too loud can cause tinnitus or deafen you. If you are coming away from a practice session with your ears severely ringing for several hours, you are playing too loudly and potentially causing permanent damage to your hearing.

To combat the need for high volume/power from your amp versus your need to preserve your hearing and to keep the cops from busting up your practice sessions, manufacturers have developed the following approaches:

• Wattage knobs

• Dummy Loads or Attenuators

• Master Volume knobs

• Variable transformers or Variacs

• Sag Circuit

If you have a tube amp with four tubes, you can remove one set of two tubes to lower the amp’s volume, but you will also need to modify the speaker’s impedance settings (see “Chapter Five—Dowsing for Tone” for more information).

Wattage KnobsSome amps come with either a Wattage knob or Wattage switch that allows you to control the number of Watts the amp is capable of producing. While Wattage controls are helpful for reducing volume, they also lower the level of sag, and therefore amp’s responsiveness.

Dummy Loads (aka Attenuators) Dummy loads are devices that go between the output of your amplifier and your speaker. The purpose of a dummy load is to absorb the amount of power you desire, and to send the remaining power to the speaker. Your amp is still making the same amount of power — it’s just that some of that power is diverted to a dummy load instead of all of it being sent straight to your speaker.

While dummy loads work great on paper, they disrupt the connection between the output tubes, output transformer and the speaker. Musical instruments aren’t like the mail; you don’t put your packet of power into the speaker cord and off it goes. The output tubes, the output transformer, the speaker cord, the speakers and speaker cabinet are all closely linked as a system, and are not just a chain of events. If you break up the system and insert another device, something bad happens sonically.

However, if you keep the amount of power being absorbed by the attenuator to a minimum, the negative effect on your tone will be less noticeable. But if you start sending 99 Watts to the dummy load and one Watt to the speaker, your tone will suffer.

Attenuators are also notoriously hard on power tubes and output transformers, often causing output tubes to burn out and output transformers to go up in smoke, as well as causing other warranty nightmares (see “Chapter Sixteen—Safety Basics”).

Master VolumesMaster Volume knobs control the level of the signal sent to the power amp after it passes through the preamp. This technique allows guitarists to overdrive or distort the preamp at low volumes. Unfortunately, the only way to get power amp distortion is to turn the volume all the way up. Preamp distortion is key to heavy metal music, but preamp distortion alone is not how good tone is made. If you are cranking the preamp, you also need to crank the Master Volume control to get the power amp distorting or you are not going to get exactly those tones that your favorite shredder is making.

Variable Transformers (aka Variacs) A variable transformer, or Variac, is a device that you use between the wall and your amplifier. You plug the variable transformer into the wall socket, and then plug your amp’s power cord into the variable transformer.

By allowing you to adjust the amount of voltage your amplifier receives, a variable transformer allows you to turn down the power the amplifier is capable of producing.

Three reasons for WanTing To conTrol volTage include: • You can overdrive the power amp at lower volumes.

• You can control your amplifier’s sound.

• You can help your amp live longer — the voltage coming out of a wall socket not only varies from socket to socket, but from hour to hour. Amplifiers live longer if they always receive 117 Volts AC (or whatever voltage is appropriate for the country you live in).

Three issues WiTh variable Transformers include: • The more you turn down the voltage, the worse your amp will sound. This problem can be solved by

having a technician add a second power transformer to your amp to supply your heaters with enough voltage. The heater transformer is then plugged into the normal wall voltage, and the remainder of your amp is plugged into the variable transformer. While this approach is certainly Rube Goldberg, it works.

• The timbre and touch responsiveness of your amp changes as you change voltage settings. Specifically, your amp’s power supply sags less and less as you turn down the voltage. Your amp will feel increasingly stiff and bright, completely obliterating one of the reasons for using the variable transformer — to enjoy cranked-to-ten tone and touch responsiveness at lower volumes.

• You can’t plug and play — you are constantly adjusting and readjusting. You cannot set a variable transformer to a specific output voltage; you can only set it to a ratio of input to output voltage. When the wall voltage changes (which it does all the time), you need to sit down with your variable transformer and a Volt meter to readjust the output voltage.

The Sag CircuitFor all these reasons, I developed the Sag Circuit. This very different power supply design allows you to dial-in power supply sag at volumes as low as ½ Watt via two knobs, Sag and Wattage. By controlling the dynamic behavior of the power supply, the Sag Circuit allows players to virtually rebuild their amplifiers with the twist of these two knobs.

Alas, the circuitry is complex and expensive to manufacture, so at the time of this publication, the only amplifiers sporting the Sag Circuit are from Maven Peal.

Well, I seem to remember pulling my head from my hands and the kaleidoscopic display of light was still happening. I had somehow stepped into one of those moments that transforms a being for the rest of his lifetimes. It seemed natural at that point to reach out for my guitar. Every note was a shimmering, shifting universe of pure love revealing itself in ways I could never have imagined. It was a long time ago, but I will always remember the way I was taught that my instrument could be a conduit to God.

Shawn Schollenbruch

Chapter Thirteen—Amplifier Basics

A guitar amplifier, whether it is based on tubes, transistors or digital processing, is composed of four major parts: the preamp, the effects control (optional), the power amp and the speaker(s). Because speakers are such a broad topic and external to the amplifier, they are discussed at length in “Chapter Seven—Speakers”

Digital amps use a computer for the preamp, and a transistor-based circuit for the power amp (sometimes, but rarely, a tube-based circuit is used). Digital preamps and other computer-based amp modelers (like GarageBand) are not discussed here because these modelers attempt to simulate the real life amps that are the topic of this book!

“Appendix D—Amplifier Block Diagrams” shows basic block diagrams for both vintage and modern tube amps. Note that due to space limitations, the full power supply block diagram is only shown in the vintage amp figure. Both vintage and modern amps employ the same basic power supply design Leo Fender borrowed from the Radiotron Designer’s Handbook over 50 years ago.”13.1”

The PreampThe preamp operates on relatively low-level (aka preamp-level) signals, such as the signal coming out of your guitar or the signals going to a mixing board. Preamp-level signals are not powerful enough to drive a speaker, hence the need for a power amplifier.

Modifying an amp’s tone and creating user adjustable functions, such as EQ (or equalizer), are much more easily done on the low-level signals that exist in the preamp. The basic idea behind all amps is to first do all the signal processing in the preamp and effects control circuitry, and then as the last step, boost the power to run the speakers via the power amp.

The funcTions of The preamp are To:• Boost the incoming signal level, creating varying degrees of distortion along the way.

• Control timbre with the tone controls.

• Define the voicing, or basic tone, of the amp.

The preamp boosts signals by multiplying the incoming signal to create an output signal. The amount of multiplication employed is called the gain, and it greatly determines how the preamp sounds, sustains and compresses. Vintage amps have very little preamp gain, while modern master volume amps have a lot.

The major difference between different channels on a multi-channel amplifier is the gain level. Gain usually occurs in different stages, with each stage multiplying its input signal to create a larger and generally more distorted output signal.

To get increasing amounts of gain, additional gain stages are added to a preamp section. Vintage amps and the clean channel on a modern amp will usually have one or two stages of preamp gain. High gain preamp channels can have three, four, five or even six stages of preamp gain to achieve the sustain and distortion the manufacturer wants.

Like the preamp as a whole, each gain stage has an input, a multiplication factor and an output. Additionally, each gain stage has a maximum output. If the input signal to a gain stage is so large that the maximum output is reached before the top of the input signal, the output is clipped, producing distortion or clipping. Driving multiple gain stages into clipping produces ever- increasing amounts of distortion.

A gain stage is centered around an amplifying (or multiplying) device. In the case of tube amplifiers, the amplifying device is a triode or a pentode preamp tube. Note that triode preamp tubes usually have two triodes in each glass container where as pentodes usually have just one. So you can get two gain stages from a triode preamp tube, or one

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gain stage and some other function like a cathode follower.

In a transistor amp, individual transistors (or op-amps) mounted directly to the circuit board are used to run each gain stage. One of the nice features tube amps offer players is that the preamp tubes, (the heart of each gain stage) can easily be changed to tweak the tone. Transistors and/or op-amps in a solid-state amp are not changeable, so you have fewer or no options for tweaking.

Since each preamp gain stage multiplies signals coming into it by such a large factor, it is important that external noise not get into the circuitry or the noise will also be amplified. While the amp’s metal chassis generally shields the circuitry inside an amplifier from external noise, the chassis isn’t tall enough to prevent preamp tubes from sticking out, making the preamp tubes vulnerable to external noise. For this reason, manufacturers often use metal shields around preamp tubes to prevent noise from getting directly into the tubes.

In addition to the amplifying device, a gain stage has a number of resistors, capacitors and sometimes inductors associated with it. Resistors, capacitors and inductors are referred to as passive components or passives because they don’t actually amplify anything.

passives in a gain sTage deTermine a number of facTors including:• How much gain the stage produces.

• What frequencies are boosted by the stage (the circuit can be arranged so only selected frequencies are boosted).

• What type of distortion the gain stage will produce (the mix of harmonics generated).

• What level of incoming signal is necessary to drive the stage into distortion.

Amp designers often consider voicing an amplifier as a last step during the design stage. Voicing an amp is basically choosing what frequencies are accentuated in the amp; these choices are implemented by selecting the exact values of the passives surrounding the gain stages.

As with all things in life, there are crappy passives and there are good ones. Good passives can cost hundreds of times more than cheap ones and can have a very noticeable effect on your tone. Great electronic components will bring the clarity, smoothness, extended frequency response, string to string definition and sustain that cheap passives simply cannot. These differences are apparent whether you are playing the amp clean or dirty, with pedals or without, and can render an amp inspirational or simply ho-hum.

The controls a preamp can offer include Gain, EQ/Tone controls, Effects controls, Reverb and Tremolo/Vibrato.

Gain ControlThe Gain knob (or Volume knob on non-master volume amps) is used to control the overall multiplication factor of the preamp. The Gain knob accomplishes this control by introducing a dividing factor into the middle of the preamp, usually after the first gain stage. This dividing factor cuts down the preamp’s overall gain — even though the gain stages are still producing the same amount of multiplication.

When the preamp is below clipping, the Gain (or Volume) controls the actual volume of the amp. Once the preamp starts to clip, higher settings on the Gain (or Volume) knob adjust the level of preamp distortion.

EQ/Tone ControlsIn addition to creating gain, the preamp is also where the tone controls (Bass, Middle, Treble or just Tone) reside. In many amps, the circuitry behind the Bass, Middle and Treble controls is arranged in a ladder formation and is therefore often referred to as the tone stack. The tone stack is also referred to as the EQ (short for equalizer), because it allows you to adjust the balance of frequencies in your amp.

There are two basic circuit tone stack configurations. In Fender Blackface-derived amps, the tone stack is immediately after the first gain stage. After the tone stack, the signal then goes on to be amplified by additional gain stages.

In Fender Tweed Bassman and Vox AC30 Top Boost-inspired amps (which include Marshalls and most modern amps) the tone stack is the last step in the preamp circuitry (placed before the effects loop and master volume controls). The tone stack in these amps is also preceded by a low impedance buffer circuit called a cathode follower.

A cathode follower circuit, which acts as a buffer, is built using one of the triodes from the next to last preamp tube. Driving the tone stack via a low impedance buffer instead of the high impedance of a normal gain stage results in tone controls that are far more effective at modifying the amp’s overall EQ. In addition, having the tone controls after the preamp distortion is generated (as opposed to before) has a significant effect on the amp’s dirty sound.

So while there isn’t a right or wrong placement of the tone stack in your amp, there is a difference in the response and tone of the preamp circuitry.

Effects ControlThe reason to place an effects device after the preamp depends on the exact nature of the effect. Overdrive, distortion and fuzz generally sound best when they are in front of the amp, that is, you plug your guitar into the effects and then go out of the effects and into the regular input of the amp. Conversely, effects such as echo, reverb, delay, chorus and flange (which all have to do with time-shifting your signal) sound better after distortion created by the preamp.

ReverbMany amps feature Reverb as a tonal option. Reverb is essentially an electromechanical echo device with a set of springs inside a metal box called a reverb tank. Inside the tank, both ends of the springs are attached to what are basically two speaker voice coils, the input and output reverb voice coils.

The input reverb voice coil is driven by a mini power amp, mimicking the speaker output of tube amps. Preamp tubes are used for the reverb “output tube” because the power needed to drive a reverb springs is much lower than the power needed to drive the speaker. And, as you might imagine, the reverb output transformer is very small. Instead of shaking a speaker cone back and forth, the input reverb voice coil shakes the reverb tank’s springs up and down.

The output reverb voice coil works exactly in reverse of the input reverb voice coil. The vibrating springs in the tank shake the voice coil in and out of a magnetic field, generating an electrical signal on par with the level of the signal coming out of your guitar. This reverb output signal (otherwise known as the wet signal) is then boosted by a preamp level reverb recovery circuit, which also employs a preamp tube.

On transistor power amps, output transformers aren’t used; likewise transistor amps don’t require a reverb-driving transformer.

After the reverb recovery circuit, the reverb (wet) signal is mixed with the original dry signal that did not go through the reverb tank via the Reverb knob.

To visualize how a reverb tank creates echoes, imagine a shaking spring stretched fairly tight. When you shake the spring once, the wave goes back and forth on the spring until it eventually dies. Each time the wave gets to the far end of the spring, the reverb tank’s output detects the motion and turns it into an electrical signal.

For this reason, never give your amp a physical jolt while playing through reverb. Because the reverb tank works on shaking springs, and the springs shake far more from physical movement than they ever could from the reverb output amplifier (aka the reverb driver), the tank creates a disconcerting clanking when jolted that can be devastating to your speakers.

Ω WARNINGNever move your amp while playing through a reverb tank as you can cause permanent damage to your speakers.

Tube-based reverb recovery circuits are usually designed around a 12AX7 preamp tube. While you can use other tube types in this position (12AT7, 12AU7, 12AY7), you will notice a lower overall reverb signal, and you will need to turn the reverb knob higher to get the same level of effect.

Before they created built-in reverb, Fender made a marvelous stand-alone three-knob reverb unit as an external effect for their amps. Three-knob reverbs used a real power tube (6K6 or 6V6) to drive the reverb tank. The Mix knob on these units is equivalent to the Reverb knob on amps with a one-knob reverb. The Dwell control governs how hot the signal going to the springs is, and it allows you to adjust how much shake you get out of the springs. The Tone control adjusts the reverb’s signal tone. These units are very versatile and produce a very lush and easily controllable reverb tone.

Some boutique amps feature three knob reverbs. The reverbs in these amps are pretty much guaranteed to be based on Fender’s stand-alone three knob reverb unit.

Tremolo/VibratoSome amps, notably Fenders after the Tweed era, feature a Tremolo circuit, which is usually mislabelled Vibrato. Tremolo is when a sound goes up and down in volume, and is relatively easy to accomplish electronically. Vibrato is the sound going up and down in pitch (like yodeling), and is rather difficult to accomplish electronically. The only

tube amp that featured true Vibrato is a Magnatone, which is significantly more complicated than most and is almost impossible to find.

Fender used a progression of tremolo circuits (labelled Vibrato on the front panel) in the brown tolex, blond tolex and Blackface amps. In the higher-power brown, and especially the blond amps, Fender used a very complex circuit to create a very lush sounding tremolo in the preamp. To keep your Tremolo working correctly, always use stock 12AX7 (aka 7025) preamp tubes in this part of the preamp.

Interestingly, the Brown Fender Deluxe has a tremolo circuit (again labelled Vibrato) that acts directly on the power tubes, actually modifying the bias to create the tremolo effect. This is the only effect I have seen that operates in the power amp realm as opposed to within the preamp.

Effects LoopsEffects loops create a method for accessing the signal after it has gone through the preamp, but before it goes through the power amp. A number of reasons exist for wanting the ability to break into the middle of your amp via an effects loop; the most common is so you can send the signal out to an external effects device, then back into the amp and out to the speakers, which is where the circuitry gets its name (looping out and back in).

You can also use an effects loop to drive one or several different power amps with the one preamp. Adding effects to the signal going to one or more power amps (known as wet amps) while leaving the signal going to other amps dry (no effects) is an excellent way to create a stereo affect and thicken your overall tone.

Generally speaking, don’t run your guitar signal through more than one preamp; but using one preamp to control more than one power amp is fine. Connect the Effects Send from your controlling preamp to the power amp(s)’ Effects Return jack(s). Since the preamps on the additional power amps will not be used, they should be turned down all the way to prevent unwanted noise from getting into the signal.

Most modern amps have a gain stage built right into the effects circuitry, which lends itself to another method often used to get more distortion. By plugging the effects send directly into the effects return, you can add a gain stage to your amp. (Thanks to Steve Posner for suggesting this alternative method of using an effects loop.)

The Power AmpThe power amp takes preamp level signals and boosts them to drive the speaker(s). While multiplication of the signal’s voltage level does occur in the power amp, the gain here is nowhere near preamp levels.

Instead, power amp increases come mainly from a multiplication of the amount of current (Amps) that the power amp is capable of producing.

Large currents are necessary to properly drive the speakers. For example, you can’t plug your iPod directly into your monster speakers at home; you will hear nothing if you do. Your iPod can only put out a few milliamps (1/1000 of an Amp) of current and your speakers need several Amps minimum to run. The power amp amplifies the voltage somewhat and the current a whole lot to create the power necessary to drive the speakers. Remember, power is voltage times current.

The Phase InverterIn a tube amplifier, the power amp usually consists of one small preamp tube (most likely in a metal shield) and larger power tubes. The preamp tube is part of the phase inverter (PI), an important component of the power amp. Transistor amplifiers also have phase inverters, but we can’t change them. You can, however, tweak the phase inverter’s preamp tube.

The phase inverter circuit takes the incoming preamp signal and splits it into two identical signals that are 180 degrees out of phase with each other (when one signal goes up, the other signal goes down). Different phase inverter circuits offer distinctly different tonal characteristics, and changing the preamp tube type used in the phase inverter changes the response and tone of the power amp.

The two outputs of the phase inverter circuit are used to drive the two sets of power tubes. With push-pull amps (which most guitar amps are), the power tubes are always divided into two sets. An amp with two power tubes has one tube per set, while an amp with four power tubes has two power tubes per set.

Almost all guitar amps are laid out so the left one or two tubes in one set, and the right one or two tubes are in the other. When one set of power tubes goes up in voltage, the other set goes down much like a seesaw.

This seesaw arrangement is why amps are called push-pull and allows the amp to make significantly more power than if the power tubes operated like the preamp tubes.

Preamp tubes operate alone and amplify both the positive and negative halves of the signal, an arrangement called single-ended. Some extremely low-power amps have single-ended operated power tubes, notably the Fender Champ which has one 6V6.

Do not attempt to lower volume by operating your push-pull amp without pairs of tubes installed. If you try to run it with just one power tube in a pseudo single-ended mode you could damage your output transformer.

0 WARNINGOperating a push-pull amp without pair(s) of power tubes can cause serious damage to your output transformer. Always run push-pull amps with pair(s) of tubes.

Presence ControlThe Presence control allows you to adjust the very highest frequencies, higher than the frequencies controlled with the Treble knob. Figure 13.1 on the next page illustrates the four frequency ranges and the knobs that control them.

The Presence control is the only EQ-type control that operates within the power amp, and therefore behaves fundamentally differently than the tone stack controls.

Bass, Mid and Treble are all basically subtractive controls, meaning that they don’t add boost; instead they adjust how much of the frequency band is taken away. In fact, turning the Bass, Mid and Treble all the way up is close to bypassing the tone stack entirely.

Conversely, turning the Presence control knob all the way down pretty much bypasses this control; while turning the Presence control up actually boosts the high frequencies.

Figure 13.1 Four Main Frequencies and Their Controls

Additionally, the Presence control actually changes the character of the high frequencies, especially when driving the power amp into distortion. Higher Presence control settings add a wildness and raspiness to your tone that the Treble knob is not capable of. Try keeping your Treble knob lower and cranking up the Presence knob for a change of pace.

The Presence control operates in what is called the negative feedback loop of the power amp. Negative feedback is used to tame a circuit and make it follow the input more exactly. A feedback loop accomplishes this with two inputs — one for the signal the amp is amplifying (the input signal) and the other for a scaled down version of the output signal.

The feedback loop circuitry compares how closely the output signal matches the input signal. Any differences are caused by distortion, and the signals the phase inverter sends to the power tubes are adjusted to try to eliminate this distortion.

Because money for nothing is just a song, the price we pay for the distortion-removing benefits of a negative feedback loop is lower power amp gain. The Presence control operates by limiting those frequencies the negative feedback loop is working on. With the Presence control turned all of the way down, all frequencies have equal amounts of negative feedback. As you turn the Presence control up, only the lower frequencies have negative

feedback (and therefore less gain), while higher frequencies have zero negative feedback (therefore more gain and more distortion).

Keep in mind that negative feedback in your amp is not at all the same feedback you experience when you put your guitar in front of your speakers. Guitar feedback is actually positive feedback — it takes a little bit of sound and makes more sound and so on, until the amp is putting out its maximum amount of power.

TransformersTube amplifiers usually have two large (and perhaps one small) somewhat rectangular metal objects living in among the tubes These two large objects are the transformers.

• Power Transformer (PT) — takes the wall voltage coming to the amp and turns it into the several different voltages required to make the amp work. All amplifiers have a power transformer.

• Output Transformer (OPT) — takes the boosted electrical signal created by the power tubes and converts it to a signal that is compatible with the speakers. With very few exceptions, only tube power amplifiers have an output transformer.

The PT is closest to where the power cord from the wall enters the amplifier. The OPT will be the other large rectangular object, usually somewhat near the power tubes.

An optional third, usually smaller, rectangular object is called the choke and is essentially half a transformer used to reduce hum in the power supply. Using a choke is very old-school, and most newer amps accomplish hum reduction in another fashion (some better, most worse).

Choke or InductorThe basic idea behind a choke, more generically called an inductor, is that magnetism and electricity are like two sides of a coin. Any electrical current flowing in a wire creates a magnetic field; conversely, a magnetic field can create current flowing in a wire.

The best way to create a magnetic field is to shape the wire into a coil, much like a Slinky. For this reason, inductors are often called coils (in fact, the coil in your car is an inductor). In electronics, a coil is referred to as a winding and the number of loops in the coil is called the number of turns.

The sTrengTh of The magneTic field creaTed by an inducTor is direcTly relaTed To:• The number of turns of wire around the inductor.

• The material inside the coils of the inductor.

• The current flowing in the wire.

When an inductor has a bunch of turns of wire with nothing on the inside except air, it is called an air core inductor. Here the magnetic field created by electricity moving through the coil is actually a series of invisible loops that can be seen using iron shavings on a piece of paper near the inductor (the shavings line up with the magnetic field). The magnetic loops inside the coil are tight, and expand from the coil’s center, outside the inductor, back into the coil’s center.

To make a stronger inductor (one with a higher inductance), we can place metal inside the coil of wire.”13.2” The magnetic field created in the metal is much stronger than an air core inductor. Likewise, the magnetic field is much tighter around the coil and does not spread into the room as much.

When DC current is first applied to an inductor (by connecting a battery to it), the inductor begins to creates a magnetic field around itself and momentarily pushes back against the voltage of the battery until the magnetic field is fully formed. Once the magnetic field is fully charged (based on the given amount of DC current trying to flow), the inductor stops pushing back on the battery and allows the current to flow as if the inductor were a plain piece of wire.

The inductor only pushes back when the current flowing through it changes (AC), not when it is constant (DC). The faster the current flowing through an inductor changes (the higher the AC frequency), the harder the inductor pushes back.

Said another way, for DC and very low frequencies, an inductor acts like a simple piece of wire, increasingly resisting the flow of current as the frequency of the signal rises. This process goes on up the scale at higher and higher frequencies until essentially no AC current can flow at all.

The way inductors handle DC versus AC is extraordinarily useful when running power tubes and creating power supplies.

The power tubes require DC to run properly, so the power supply has to turn the AC coming from the wall socket into the DC.

all poWer supplies accomplish This by:• Turning the positive-and-negative-going AC into positive-only via the rectifiers, and

• Smoothing out the rectified AC to make DC via the filter capacitors.

The problem here is that the filter capacitors are not perfect at creating smoothed-out DC. While an amp can live with less-than-perfect DC, it will hum a lot. More expensive capacitors can help make an amp less noisy. A big fat resistor before the filter capacitors will also cause the DC to be much smoother, but a lot of that power will be wasted turning into heat in the resistor.

As is usually the case, the much more expensive option of putting an iron-cored inductor before the filter caps solves the problem. The tendency of an iron-core inductor to push back on the AC and to let DC through makes the power supply many times quieter than even the resistor option would. In addition, instead of turning AC into unwanted heat, the AC is smoothed out to create useful DC. An iron-core inductor is called a choke because it literally chokes the AC and lets the DC through.

Because of the lower voltages involved, transistor amplifiers generally can get away with using only very large-capacitance filter capacitors in their power supplies. Not that a choke couldn’t help these amps as well, but cost is everything in a transistor amp.

Inductor SaturationWhile adding a material like iron to the inside of an inductor can increase the magnetic field created by the flowing current, there is a price to pay. When more and more current flows through an iron-core inductor, the magnetic field created in the core also increases — but only up to a point — the point at which more current begins to cause the magnetic field increase to slow down.

This phenomenon is called core saturation and it looks surprisingly like a tube being pushed into clipping. When a tube circuit clips, more input voltage is put into the circuit, but the circuit is incapable of producing more output voltage. With core saturation, more current is put into the inductor but the core material is incapable of supporting a stronger magnetic field.

Magnetic NoiseBecause an inductor creates a magnetic field that goes through the coil’s core, outside and back in again, the exact shape of the magnetic field can be of concern. When the magnetic field outside the coil stays relatively close to the coil, all is well. But if the magnetic field loops out into the room where you have your guitar (which of course has magnetic pickups), your guitar will literally pick up some of that noisy magnetic field.

The coil/core assembly can be shaped in various ways to make the external field both smaller and closer to the coil. The traditional choke’s core shape is rectangular with a rectangular hole in the middle. The coil of wire is wrapped around one of the legs of the rectangle and then covered with sheet metal. For efficiency, the core is not usually solid metal, but made from a stacked-up bunch of thin metal sheets. If you ever have a chance to look at a traditional choke, you’ll easily see the coils and metals sheets.

This arrangement for the core and choke is a huge improvement over having just the coil wrapped around a piece of metal. Because the core goes through the middle of the coil windings, as well as outside the windings and back in again (forming a complete loop), the magnetic field created by the current flowing through the coil stays largely inside the core as it loops.

Creating an iron path for the magnetic field to easily flow through (as opposed to forcing the magnetic field to leave the iron and come back in), makes for a much stronger and quieter inductor (since the magnetic field isn’t spraying into the room as much).

Toroidal InductorsWhile the rectangular inductor is a wonderful device, it still isn’t perfect and the coil’s magnetic field is still not 100% confined to the inductor’s core. Although a rectangular shape lends itself to easy manufacturing, its sharp corners are not easy paths for magnetic fields to stay within.

To get more complete containment of the magnetic field, an inductor can be designed to be the shape of a donut using a circle with a round hole in the middle. The mathematical name for this donut shape is a toroid. Inductors made with a doughnut-shaped core are called toroidal inductors.

Toroidal cores are ten times better at keeping magnetic fields confined to the core than rectangular-core inductors. Unfortunately, wrapping a coil of wire around a toroidal core is a much more difficult manufacturing process. Once again, you get what you pay for — if you want a better choke, you need to be willing to pay for a toroidal inductor. Fortunately, the prices of toroidal inductors (and transformers, which we will get into next) have been coming down as the manufacturing technology matures.

Transformer BasicsA transformer is basically an iron-cored inductor with a second coil of wire wrapped around the core. The primary winding refers to the original coil of wire/winding around the core. The secondary winding refers to the second coil added around the core.

The basic concepTs behind Transformers are:1. Electrical current flowing in the primary winding creates a magnetic field in the core.

2. The core’s changing magnetic field (or AC) creates electrical current in the secondary winding which is unaffected by unchanging (or DC) current in the primary winding.

In a perfect transformer, the AC current and voltage in the secondary winding is directly related to the AC current and voltage in the primary winding. Specifically, the current times the voltage in the primary (power) is exactly equal to the current times the voltage in the secondary winding (secondary power). A perfect transformer loses no power.

While the current times the voltage on each side of a transformer have to be equal, the voltage or current on each side do not have to be equal. For example, the voltage on the secondary side can be a whole lot lower than the voltage on the primary side. In which case, the current on the secondary side would be a whole lot higher than the primary side. This transformation of high voltage/low current to low voltage/high current (and visa versa) is exactly where transformers get their name.

The voltage/current relationship between the two windings is controlled by how many turns of wire are in the primary winding (referred to as N1) compared to how many turns of wire are in the secondary winding (N2).

So if N1 is equal to N2, the voltage on the primary side of the transformer is equal to the voltage on the secondary side of the transformer, and the currents on each side are equal.

But, if N2 is bigger than N1, the voltage on the secondary is larger than the voltage on the primary. This design is called a step-up transformer. When N2 is smaller than N1, the voltage on the secondary is smaller than the voltage on the primary. This design is called a step-down transformer.

The ability to easily transform voltage is absolutely vital to every electrical device you plug into the wall, and this is where Nikola Tesla went head-to-head with Thomas Edison. Tesla, working for Edison, was the inventor and major proponent of an AC-based electrical power distribution system. Edison (a big DC proponent) was too stubborn to listen. Fortunately, Tesla went to Westinghouse and the world mainly operates on an AC distribution system (although DC is better for very long lines like those going along the ocean floor).

Guitar amp power transformers add more than one secondary winding to produce more than one output voltage. One secondary winding runs the tube heaters (very low voltage), and another runs the tubes themselves (very high voltage). A third winding runs the biasing circuitry, and there may be more depending on the amp’s complexity.

Because different wall voltages are available in different countries, your amp may have a voltage-selection switch on the back that allows you to change the wall voltage your amp can accommodate. This selection switch changes the number of windings that are in use on the primary side of the power transformer.

The Output TransformerAlthough similar to the power transformer, the output transformer (OPT) has a more complicated job. The AC signal produced by the power tubes is on the order of 500 Volts peak, while the AC your speakers need to operate is around 56 Volts peak (100 Watts into a 16 Ohm speaker).

The goals an opT needs To achieve are To:• Step down the AC voltage from the tubes to the speaker voltage.

• Produce 16, 8 and 4 Ohm outputs, matching the speakers to deliver maximum power.

• Remove the high DC voltage used to make the tubes run and only allow AC to pass on to the speakers (this function is easy since transformers can’t pass DC).

• Combine the out-of-phase signals from each set of power tubes into a single signal (this combination

thankfully automatically removes even harmonic distortion). A tap in the center of the primary side of the OPT (aka a center-tapped winding) accomplishes this goal. One set of tubes is connected to one half of the primary winding while the other set of tubes is connected to the other half.

• Allow signals ranging in frequency from very low (the low E string on your guitar is 80Hz) to fairly high (at least 10kHz is required to avoid making the amp too dark) to pass through unmolested. While the power transformer only has to operate at the frequency of the wall voltage (50 or 60Hz), the OPT has to handle a large range of frequencies.

• Saturate the core at roughly the same power levels as output tube clipping occurs. While core saturation is not an absolute requirement, it really adds to the smoothness of an overdriven amp.

Winding an output transformer is a true art, including choosing materials for the core, winding configuration and winding insulation.

For all of these reasons, an OPT can really make or break the tone of your amp, especially when pushing the power amp into distortion. So, if you are looking to upgrade your amp, investing in a high quality OPT will be money well spent.

Speakers and the Power AmplifierWhile speakers are covered in detail “Chapter Seven—Speakers” they are an integral part of a tube power amp.

Although speakers appear to be relatively simple electronic devices, they really aren’t. Speaker frequency response curves (available at most manufacturers’ web sites) show quite complex behavior. Factor in speaker overdrive, which frequency response curves do not, and the true behavior of guitar amp speakers becomes wildly complex.

Where the really interesting aspect of speakers comes into play is in the nature of how a transformer works.

Almost anyone with a solar panel can now sell electricity back to the power company. This is possible because the flow of power through the street-pole transformer allows electricity to flow both ways — to your house or from your house.

As far as the electrical company is concerned, the electrical usage (or generation) at your house is happening on the power line side of the street-pole transformer as opposed to your house side.

So for example, let’s say the voltage coming to and from your house is the usual 240 Volts. The voltage on the power line is often 2400 Volts. If the current to your home is 10 Amps, the current on the power line side of the pole transformer is 1 Amp; in the end 240 Volts times 10 Amps = 2400 Watts = 2400 Volts times 1 Amp.

So from the power line side of the pole transformer, your house’s electrical Wattage requirements look exactly as they do on the house side of the transformer. From a power point of view, it is as if the pole transformer is not there at all.

Your tube power amp behaves just like the power company. The voltages and currents present at the OPT secondary (which are going to the speakers) look to the power tubes like multiplied versions of those same currents and voltages at the primaries of the OPT (the power tubes). The overall Wattage is exactly the same on either side of the output transformer as if the transformer were not there.

So as far as your power tubes are concerned, there is no transformer and the speaker is scaled and connected directly to the tubes.

Just as resistors, capacitors and inductors are associated with each gain stage in the preamp, similar resistors, capacitors and inductors are associated with the power tubes. However a lot of the power amp components are essentially embodied in the speaker’s complex electrical behavior. So you can and should think of the speaker as being an integral part of a tube power amplifier.

Because speakers are such an integral part of the power amplifier, replacing your speaker with a dummy load or attenuator is like sticking your hand in your amp and ripping out a whole bunch of cool, complex circuitry and replacing it with the equivalent of a caveman’s club. While a club will get the job done, it will not be the same as the original, so don’t expect it to be.

Additional hazards to using an attenuator are discussed in ”Chapter Twelve—A Word About Volume”

So if you can, drive a real speaker, even if you have to put it in a closet and mic it. Micing the speaker also gives you the opportunity to add effects after the power amp and speaker distortion, instead of before, which is often a better idea anyway.

Line OutAs a convenience for recording or driving other amps or effects processors, many amplifiers have a Line Out jack. Although you can use the Line Out to get a preamp level signal instead of micing the speaker, using the Line Out will never sound as realistic as micing.

A Line Out is a preamp level signal derived from the signal sent to the speakers. So Line Outs have circuitry that knocks the speaker level signal down to a preamp level signal, while some attempt to simulate the speaker’s frequency response.

Chapter Thirteen Footnotes

13.1 With the exception of Maven Peal’s Sag Circuit and dual and triple rectifier amplifiers.

13.2 Because the windings are all coated with insulation, the metal inside the coil wire does not directly touch the coil wire.

… there are moments playing the guitar when the music seems to flow from thought to sound through your fingers through the guitar through the amplifier and back to your thoughts… when you can hear the rest of the band as yourself and everything is in it own space… when your notes are articulate and respond to the slightest nuances in your fingers… after forty years of playing guitar these are the moments that continue to inspire.

Jeff Chapman

Chapter Fourteen—Distortion Basics

When an amplifier (or any other electronic circuit) produces distortion, the output is not a simple multiplication of the input signal. For example, if you put an electrical waveform into a circuit that produces no distortion, you should get out that exact waveform, only bigger with no modifications whatsoever. In the audiophile/high end stereo world, such a circuit is the Holy Grail and is called a straight wire with gain — it also does not exist in the real world.

Before I go on, I need to clarify the difference between gain and distortion. And to do that, I need to explain a sine wave.

A sine wave is defined as the most primitive shape of a wave. If you put a dot on a ball, roll the ball and plot only the up and down part of the path traveled by the dot over time, you will have a sine wave.

GainGain is simple multiplication; a reproduction of the input signal, only bigger. The easiest type of distortion to understand, and the most useful, is when the input signal to a gain stage is high enough that the multiplied output signal is larger than the amp or gain stage is capable of reproducing.

But even when the output signal is well within the amp’s capabilities, distortion still exists. This is because, to date, humans have only been able to design four fundamental types of amplifying devices,”14.1” and not one of them is perfect. Vacuum tube triodes are the closest we’ve been able to get.

DistortionThe degrees and types of distortion are quite numerous and, luckily for guitar players, some are extraordinarily fun.

Of the many types of distortion in the sound spectrum, quite a few are present in guitar amplifiers. The easiest type of distortion to understand is called clipping, so I’ll use clipping as an example.

While some distortion is subtle, clipping is brute force and occurs when a circuit is asked to produce more output than it is capable of producing. Clipping is lot like asking a tall person to stand in your basement — a point is reached from which there is nowhere left to go.

Let’s say you have a gain stage that multiplies the input signal by 100, and that the output can — at most — go between plus and minus 10 Volts. All is well when the input to the gain stage goes between plus or minus 1/100 of a Volt (0.01 Volts), because the output will only fluctuate between plus or minus one Volt.

But when the gain stage’s input increases to plus or minus two Volts, you might think that the output should go between plus or minus 200 Volts. But this isn’t possible because the circuit’s output can only be at most plus or minus ten Volts, regardless of the input signal.

So what happens? As soon as the output waveform goes to plus or minus ten Volts, the wave stays at that level until the output drops back below ten Volts. The tops of the input waveform are “clipped off,” just as if you had clipped off the tips of the bushes in your yard.

Clipping Hard and SoftFigure 14.1 shows an example of a typical sine wave while Figure 14.2 shows a sine wave that has been hard clipped. The exact shape of the wave’s corner after clipping determines the tone of the distortion. If the clipping

has a very sharp corner where the wave transitions from not clipped to clipped, the tone will be harsh, bright, like a bucket of bees. This type of clipping is called hard clipping, and most transistor amps suffer from it.

Figure 14.3 shows an example of soft clipping, where the wave form more gently transitions from a normal sine wave to the clipped off top. Soft clipping is much smoother, fuller, pleasing to the ear and is typical of most tube amplifiers.

Figure 14.1 Typical Sine Wave

Figure 14.2 Hard Clipped Sine Wave

Figure 14.3 Soft Clipped Sine Wave

For the next section, try not to think of a waveform as what it looks like on an oscilloscope (as in Figures 14.1 through 14.3); instead, think of various frequencies or harmonics that make up the waveform as light and color.

HarmonicsWe all know from grade school science that if we put light through a prism, the light splits into separate but enmeshed component parts, just as a rainbow is white sunlight split into separate yet enmeshed colors. Sound is very similar, and our ears do a great job of splitting a complex sound into its component parts.

Instead of colors, our ears break down sound into detectable sine waves (coincidently — or not — the colors we see are also sine waves).

In reality, every sound wave (or any wave for that matter), is a grouping of sine waves of various frequencies, just as white light is all of the colors of the rainbow combined.

With any wave, the lowest frequency sine wave is called the fundamental. All other higher frequency sine waves are called harmonics. The frequencies of the harmonics are always integer (2, 3, 4, 5 etc.) multiples of the fundamental frequency.

Even multiples of the fundamental are called even harmonics, and odd multiples are called odd harmonics. Two sine waves separated by an octave means that the higher frequency wave has a frequency double that of the lower wave. For example, a 200Hz sine wave is one octave higher than a 100Hz sine wave.

Figure 14.4 shows a series of sine waves that includes the fundamental (the largest sine wave) and the first couple of odd harmonic sine waves (specifically the 3rd, 5th and 7th harmonics, each with decreasing size). The waveform shown in Figure 14.5 is the result when this series of sines waves is added together.

Figure 14.4 Sine Waves Showing the Fundamental and a Series of Odd Harmonics

Figure 14.5 Fundamental with Odd Harmonics Combined

Similarly Figure 14.6 shows the fundamental and a series of even harmonics of decreasing size, (the 2nd, 4th, 6th and 8th). The waveform shown in Figure 14.7 is the result when this series of sines waves is added together.

Figure 14.6 Sine Waves Showing the Fundamental and a Series of Even Harmonics

Figure 14.7 Fundamental with Even Harmonics Combined

Figure 14.8 shows the wave form that results from adding the fundamental and all of the even and odd harmonics in Figures 14.4 and 14.6 together.

Figure 14.8 Fundamental with Odd and Even Harmonics Combined

The summed up waveforms of Figures 14.5, 14.7 and 14.8 illustrate how different mixes of harmonics produce seriously different tones. For example, the waveform in Figure 14.5, approaching a square wave, will give a more classic power amp distortion tone. The even harmonics-only waveform in Figure 14.7 looks really nasty and sounds that way too, much nastier than any amp ever could. The waveform containing both the even and odd harmonics in Figure 14.8 produces a very metal type sound.

Figure 14.9 Sine Wave Clipped on One Side Producing Even Harmonics

Tone is all about the level of the various harmonics in the signal — harmonic content defines tone. A saxophone produces only odd harmonics, while a plucked guitar string creates a mixture of both odd and even harmonics.

In fact, all forms of distortion can be thought of as the addition of harmonics in various proportions to a signal. The exact mix of harmonics is the heart of the various levels and types of preamp and power amp distortion. Power amp distortion in a push-pull amp adds only odd harmonics, while preamp distortion adds predominately even harmonics with some odd harmonics.

Figure 14.10 Sine Wave Clipped Asymmetrically Producing Even and Odd Harmonics

Harmonics and ClippingWhen a waveform is symmetrically clipped, both the top (positive) and bottom (negative) sides of the waveform are clipped equally, and all the added harmonics are odd. The clipping in Figures 14.2 and 14.3 are examples of symmetrical clipping creating odd harmonics.

When only one side of the waveform is clipped and the other side is left alone, all the harmonics are even. Figure 14.9 shows an example waveform that has been clipped on only one side. If the clipping is almost but not quite equal on the top and bottom, the harmonics added are a mix of even and odd, as shown in Figure 14.10.

Sub-HarmonicsWhen a signal is modified by running through a distortion—creating circuit, the circuit will sometimes not only produce added harmonics, but also sub-harmonics. Sub-harmonics are produced by dividing the fundamental frequency by an integer (2, 3, 4, 5 etc.).

For example, when the fundamental frequency is 100Hz, the sub harmonics are 50, 33 1/3, 25, 20Hz, etc. Generally speaking, sub-harmonics create a farty tone and are very heavy on the ears.

To combat the addition of sub-harmonics, manufacturers add filter circuitry that reduces the lower-level frequencies, which in general works great — until a either a Gain knob is added or you set your guitar’s Volume so low that the circuit is no longer distorting. Now the circuitry that is supposed to be reducing the sub-harmonics begins to produce a really thin, anemic sound when the amp is not distorting. And rightly so— the filter circuitry reduces all

of the lower frequencies, even when distortion is not occurring.

An example you might be familiar with is a non-master volume Marshall using only the Bright input. When this amp is not being pushed into distortion, the Bright input can be ear-piercingly bright, thin and not much fun to use (the ice-pick-in-the-forehead effect).

In this case, the Bright input has a built-in filter. So while it might be counter-intuitive that turning up the gain (in this case, the amp’s Bright Volume knob) will make this undesirable tone go away, that is how it works. Turning up the Volume creates more distortion, which makes the lower frequency sub-harmonics easier to hear, fattening up and rounding out the sound. Without the filter, the Bright input would produce too much bass when distorting.

In fact, many boost-type pedals accentuate the treble end of the spectrum far more than the bass end to avoid the fartiness that can be added by sub-harmonics. When pushing an amp into distortion, the higher frequencies should be emphasized, not the lower ones.

Alas, too much of a good thing is never good, and adding too much in the way of high harmonics is not a good thing. When the mix of harmonic distortion contains too many high harmonics, the distortion sounds unfocused, piercing and generally like you threw a bucket of bees into the amp — an all too common description for far too many high gain preamp circuits.

Unfortunately, because you can’t control the mix of harmonics your amp creates when pushed to distortion”14.2”, you need to find an amp that behaves the way you like.

That Ringing Fuzz Sound Sometimes when a gain stage clips, it produces a little extra ringing right after the clip. This effect can happen with power amp distortion, as well as preamp distortion, especially if you have a poorly designed amp with bad components. Bad output transformers are notorious for this effect.

Quite often, an amp that rings when distorting will also produce a bunch of non-musical fuzz on the note. Both of these effects can get really old after a while. While I have heard some claim that this ringing fuzz is somehow part of the organic sound of a good amp (I’ve also heard it ridiculously argued that hum is also organic), most manufacturers have been trying to eliminate ringing fuzz for decades, with varying degrees of success.

When CBS took over Fender from 1968 to 1986, the new CBS engineers actually created a big problem when they attempted to remove ringing fuzz by morphing Blackface amps into the Silverface amps. They did this by adding solid state diodes around the output transformer on some models. While the engineers felt these diodes would “protect” the amp from ringing; instead the diodes exacerbated the problem. So if you have a Silverface amp built between 1968 and 1986, have your tech check to see if you have those diodes. If so, take them out.

Attenuators and Dummy LoadsUsing an attenuator or speaker dummy load instead of a speaker can create or exacerbate the ringing issue. In some cases the ringing can be so bad that it destroys the amp’s output transformer.

As always, please try to keep attenuator usage to a minimum if you can.

Opportunities for DistortionThere are a large number of opportunities to add distortion to your tone. The block diagram in Figure 14.11 shows the various opportunities for creating distortion in your gear. The sections that follow discuss each of these opportunities in detail.

Figure 14.11 Opportunities for Distortion in a Guitar Amplifier

Overdrive and Boost/Distortion and FuzzThese terms are used frequently, often interchangeably, when they actually refer to very different tones. Technically, engineers call anything coming out of an amp that is not a carbon copy of the input “distortion.” But guitar players require more words to describe various types of distortion, so we use slightly different language to describe the sounds our amps make.

Overdrive and BoostOverdrive is when the guitar signal gets a boost before it goes to the amp. When you overdrive your amp, you are pushing the amp further into distortion than you could with just your guitar — as if your guitar’s Volume knob suddenly went to 20 instead of 10.

Non-master volume amps are easier to overdrive because the gain provided by the preamp, while not excessive, isn’t being turned down via a master volume. But overdrive is still cool with master volume amps.

Overdrive is often associated with non-master volume amps;”14.3” overdriven tone implies that some power tube distortion is occurring, often with an effects pedal pushing the tubes (either preamp and/or power amp), as opposed to the tubes’ introducing distortion all on their own.

Many overdrive pedals are available to help you push your amp from clean to dirty, with different pedals offering different tones. Overdrive pedals feature a very mild (hopefully) tubey distortion within themselves. A good overdrive pedal will allow you to create distortion within the pedal, as well as allow you to pass a clean, but treble heavy boosted signal when you set the knobs just right.

The Tube Screamer is the archetype overdrive pedal with a signal path that includes Gain, Tone and Volume controls.

The Tube screamer overdrive pedal signal paTh includes: • The Gain knob — adjusts how much the guitar signal is boosted at the start of the pedal’s circuitry.

With the Gain turned down, the pedal makes no distortion. When the Gain knob cranked, the pedal creates a mild distortion designed to simulate tube distortion.

• The Tone knob and associated circuitry — adjusts (from low to high) the range of boosted frequencies.

• The Volume knob — adjusts how hot the signal coming from the pedal is.

The classic rock/blues True overdrive approach To The Tube screamer is To:1. Set the Volume knob all the way up.

2. Set the Tone knob a little past 12:00.

3. Set the Gain knob way down until the pedal produces no distortion.

With this approach, the pedal’s output is higher than the guitar’s, boosting the upper end of the frequency range, yet the signal doesn’t have any distortion. This hotter signal (higher voltage) pushes the amp into overdrive.

Boost pedals generally do not create distortion within themselves. Instead a Boost pedal simply increases the guitar’s volume, usually increasing the treble end of the spectrum much more than the bass end. Focusing on the higher treble frequencies helps eliminate some of the fartiness associated sub-harmonic distortion.

Distortion and FuzzDistortion and fuzz pedals are supposed to make their own unique sound as pretty much stand-alone devices (they are not really tuned to work in conjunction with your amp the way a boost or overdrive pedal is).

Distortion Pedals Instead of the small amount of distortion that an overdrive pedal can make within itself, a distortion pedal makes a tremendous amount of distortion. Distortion pedals are used to radically modify the sound as opposed to just overdriving the amp. In fact, distortion pedals can make so much distortion by themselves that you don’t necessarily need to overdrive your amp at all.

Of course, turning a distortion pedal’s Output Volume way up allows you to overdrive the amp also, but you will be hearing much more of the pedal’s tone, whereas the goal of most overdrive/boost pedals is to get the amp to create the distortion.

Fuzz PedalsA fuzz pedal is used to take the clipping concept to an extreme. With enough gain stages and sharp-cornered clipping, a fuzz pedal takes the nice, rounded guitar signal and turns it into a virtual square wave.

The sharp-cornered clipping of fuzz pedals produces copious amounts of high harmonics and drastically modifies your tone. A good fuzz pedal will also have enough output volume on tap to overdrive the amp as well as to producing clipped distortion.

Try setting a fuzz pedal’s Gain level a little on the low side to get some fuzz, and then set the Output Volume really high to overdrive the amp.

Preamp vs. Power Amp DistortionAC/DC, especially on their earlier albums, plug their guitars straight into non-master volume amps, and their sound is distorted yet clear. Early Van Halen, early Rush, the Allman Brothers and Cream are all great examples of guitars plugged straight into non-master volume amps. While the tone of all of these bands is definitely very distorted, a clarity and presence exists that differs from a lot of modern distorted amp tones.

The extremely high amount of preamp distortion (or gain) available from modern preamp distortion circuits lends itself to wild guitar techniques that would otherwise be too difficult to play, or just not as interesting to listen to. For example, Joe Satriani has a very compressed, sustaining-forever even sound that is not jagged-edged and dynamic like AC/DC, or as clear as the Allman Brothers. Satriani needs the sustain and extreme amount of gain to make his technique shine, and it is a great example of what good, over-the-top preamp distortion can do for you.

To check out some really heavy preamp distortion sounds, any metal band is a good starting point (some have better tone than others).

In the middle of the spectrum, however, Slash from Guns N’Roses and Velvet Revolver is a great example of the moderate preamp distortion available from a relatively lower gain master volume amp, the JCM800. Of course, Slash is getting quite a bit of power amp distortion also since he cranks the master volume pretty high — a true balance of preamp and power amp distortion.

Distinct differences exist in the way preamp distortion and power amp distortion are generated and in the resulting harmonic content. Understanding these differences is helpful for finding the tones you are looking for.

Preamp DistortionPreamp distortion involves single-ended gain stages. In electronics, single-ended means one device is doing the amplifying, with only one signal path going through the circuit.

The extreme opposite of single ended is push-pull, where one device amplifies the positive half of the signal, and another device amplifies the negative half of the signal equally. The two half but equal signals are then added back together.

Single-ended circuits generally do not distort the positive and negative halves of a signal equally. This asymmetry generates even harmonics (but some odd harmonics sneak in because the clipping is not totally asymmetrical). Figure 14.10 shows an example of a signal that has been asymmetrically clipped.

Additionally, the spread of harmonics created by preamp distortion is usually very wide with a lot of high harmonics. So unless a manufacturer is very careful, preamp distortion can become a bucket of bees with too much emphasis on high harmonics. The amount of gain used in many preamp circuits is so high, it causes compression creating a lack of touch responsiveness (the notes sound the same no matter how hard you hit the strings).

Compression is an easily misunderstood term, and technically refers to when the signal level coming out of the circuit is largely independent of the signal level going into the circuit. Musically, compression in a distorted amp refers to so much gain that no matter hard or soft you play, the amp is pushed to clipping.

On a more positive note, preamp circuits lend themselves to tone-shaping circuitry not possible with a power amp circuit creating a world of possibilities for tremendously thick harmonic content. Ample room for creativity in modifying the tonal balance, or voicing, is available to the preamp designer.

Power Amp DistortionPower amp distortion is produced by a number of circuit elements that are very different from preamp gain stage circuits. The phase inverter is one of these circuit elements, and produces its own unique distortion that causes notes to become extremely thick. Different phase inverter circuits affect how the overall power amp distorts and feels.

Phase inverters in older Tweed amps distort more easily, while later Tweed and Marshall-style amps have phase inverters that “hold together” pretty well under overdrive conditions. The phase inverters in Fender Blackface-style power amps hold together extremely well and are quite difficult to distort. When they do, they can be extremely thick.

Power tubes distort very differently than the way preamp tubes distort. Power tubes tend to clip less harshly with less sharp corners compared to preamp tubes. More rounded corners translates to a predominance of lower-order harmonics — which is why power tube distortion has a more focused, clearer tone without the bucket of bees tendencies found in preamp distortion.

The output transformer (OPT) can create very smooth clipping all by itself, which is quite noticeable when comparing most Fender amps to most Marshalls. Fender transformers are much easier to saturate — an engineering term for saying they distort much more easily. Fender’s OPTs are one of the reasons Blackface amps produce really fat distortion even though their phase inverters hold together much better than Marshalls’.

Another difference between preamp and power amp distortion involves the common push-pull power amp design. Because the resulting waveform from any push-pull amp is inherently balanced in its positive and negative sides, push-pull power amps produce only odd harmonics when distorted. The lack of even harmonics leads to a more saxophone-type sound that is much clearer than distortion produced by a preamp. Figure 14.3 Soft Clipped Sine Wave shows a wave that has been evenly clipped with rounded corners producing only odd harmonics (my personal favorite form of wave!).

Power Supply SagFor guitarists, another big difference between preamp and power amp distortion is power supply sag. When you push an amplifier into power amp distortion, you are pushing the power supply beyond its normal limit causing it to sag. A good analogy is starting your car with the headlights on. Turning the ignition key causes the lights to dim due to the battery voltage dropping off (or sagging) because now high current is going to the starter motor. Really pushing your amp’s volume also causes its battery (or power supply) to dim or sag.

While vintage tube-rectifier-based power supplies sag more than solid state rectifiers, all traditional power supplies sag to some degree. When an amplifier begins to sag, it affects the character of the distortion produced by both the power amp and the preamp.

Preamp distortion only with no power amp distortion and lots of power supply sag is impossible.”14.4” Power supply sag happens only at your amp’s highest volumes.

At higher sag levels, clipping in both the preamp and power amp becomes more rounded or soft, producing fewer high harmonics and a smoother tone. The sag effect is most pronounced at the beginning of the note (the attack part of the note’s volume envelope) and less pronounced toward the end of the note (the sustain part of the note’s volume

envelope), and it makes the amp feel like it can’t quite keep up with you.

The attack of a sagging amp is muted, and your guitar strings feel more like rubber bands. In general, the amp feels softer and squishier. A sagging amp is said to breathe as it changes character with each and every note.

These changes in an amp’s tone and response is one of the biggest reasons that you need to find a space where you can crank your amp up, regardless of the type of music you play.

Some amplifier manufacturers now offer two sets of rectifiers, tube and solid-state, to try to give the musician some small amount of control over the amp’s sagginess. My guess, however, is that 99% of players who have these amps never have the opportunity to turn up the Master Volume loud enough to get anywhere near the volume required to kick in power supply sag. Try to get an hour of studio time somewhere and really, really crank that baby up and see what power supply sag is all about (don’t forget your earplugs). Playing an amp with a good power amp pushed to distortion is a wonderful experience.

Speaker DistortionWhen you get a chance to crank your amp loudly enough to produce power amp distortion, you will quickly discover speaker distortion.

Speakers also distort in various ways when pushed beyond their rated limits. Speaker distortion tends to be odd harmonics-based, and can often be very smooth. The sound of an overdriven Celestion Greenback à la Duane Allman, is a classic example of singing, smooth, woody speaker distortion.

However when pushed, some speakers exhibit cone cry, little ripples of motion on the cone that add a nasty little high-end ice-pick effect that you really don’t want. Cone cry happens when the motion of the speaker cone goes somewhat out of the control of the voice coil and surround (see “Chapter Seven—Speakers”). While not all speakers exhibit cone cry, 12" speakers tend to be most guilty of this undesirable type of speaker distortion.

if your favoriTe speaker is crying on you, Try These Techniques:• Turn down the amp’s Volume knob.

• Turn the Presence knob all the way down, and adjust the Treble knob to add the desired brightness.

• Double up speaker cabinets so no one speaker receives too much Wattage.

If none of these approaches works, you need a new speaker.

Different speaker types exhibit other interesting behaviors when really pushed. For example, British-made Celestion Vintage 30s can produce a harmonic overtone that sounds as if you are playing two notes. Alas, I am not so accomplished, but I’ve heard Sonny Landreth take advantage of this effect with wonderful results.

Chapter Fourteen Footnotes

14.1 The four fundamental types of amplifying devices, in order of perfection, include vacuum tubes (triodes, tetrodes or pentodes), metal oxide semi-conductor field effect transistors (MOSFETs), junction field effect transistors (JFETs), and bipolar junction transistors (BJTs).

14.2. With the exception of the Maven Peal Sag Circuit, which allows you to control the mix of harmonics via the Sag knob.

14.3. Distortion produced by a non-master volume amp is not pure power amp distortion. When you crank up the volume (Gain) knob high enough on a non-master volume amp to push the power amp into distortion, the preamp is also distorting to some degree. However, the level of preamp distortion is just not as high as in an amp specifically designed to distort the preamp to tremendous levels, such as with a master volume amp.

14.4. With the exception of Maven Peal’s Sag Circuit, the only power supply design that allows you to dial-in the amount of power supply sag, from absolute zero to over the top, regardless of how much power the amp is producing.

Guitars are like women! No matter how beautiful they are, if they do not feel right in the dark with your eyes closed it wasn’t meant to be.

Alberob

Chapter Fifteen—Tube Basics

At this point, you can rightfully ask, If Dave is so high on tubes, and transistors don’t inherently perform comparably, why use transistors or computers at all in guitar amps?

The answer is, of course, money. Most of the transistor’s technical shortfalls are easily overcome by stuffing tens if not hundreds of extraordinarily cheap transistors into a very small space (not to mention using computers which have millions of transistors). The end result is an overall smaller circuit that is much cheaper to manufacture than a circuit designed around tubes. In addition, engineers can perform wonderful design tricks that make an overall transistor circuit behave relatively nicely.

It is basically a trade-off between a few very good devices (tubes) used in relatively simple circuits versus an army of relatively poor, but well-matched devices used in extremely sophisticated circuits (known as integrated circuits or ICs).

In a stereo, and other well-behaved environments where the electronics are not being purposely overloaded, transistor circuits perform wonderfully. But that all changes if pushed beyond their linear (ultra clean) range. When pushed into clipping, ICs can create extremely nasty situations like latch-up or go into thermal runaway — both of which can destroy some or all of the circuitry.

Another downside is that ICs are nearly impossible to repair. The simplicity of tube circuits makes repairs not only possible, but cost effective — not the case with complex transistor circuits. When repairing a modern stereo, the most cost-effective route is to remove the entire printed circuit board and replace it with a new one.

The following are two summaries of the pluses and minuses of using tubes in guitar amplifiers.

Tube Strengths• Tube distortion offers a more musical mix of harmonics and feels more alive than transistor distortion.

Rectifier tubes provide a saggier, vintage response.

• Tubes are replaceable, so you can modify the sound of your amp (with cathode and external biasing, you can easily modify your sound in minutes).

• Tube amps are easier to repair than transistor amps.

• Tubes are not subject to latch-up and other IC idiosyncrasies.

• Tube amplifiers seem louder than transistor amplifiers of equal Wattage rating. This phenomenon occurs because tube amplifiers have more headroom, and tubes themselves don’t have the same hard clipping characteristics transistors do.

• Tubes are less susceptible to damage from a nuclear-explosion-induced electromagnetic pulse, so you can rock on long after they drop the big one.

• Tube amps retain a higher resale value than transistor amps.

• Tubes have a kind of fetishy vibe about them. People collect them and the boxes they come in — even with modern tubes. (Talk to someone who has some great EI tubes made during the 1990s in the former Yugoslavia, and you’ll see what I mean.) Really old tubes are like priceless little jewels that people collect for investment and other non-musical purposes.

Transistor Strengths• Transistors almost never need replacing.

• Transistors are sturdy; they are not contained in easily breakable glass bottles.

• Transistor rectifiers give a punchy, more modern response than tube rectifiers.

• Transistor circuits are generally safer to play and work on because they do not operate at lethal voltage levels.

• Transistor amps help conserve energy — they take less power from the wall than tube amps do to make the same amount of power.

• Transistor amps are much lighter than tube amps because they don’t require a large output transformer, a large power transformer and the beefy chassis required to mount them.

• Transistors are used in many other products, assuring their availability. Tube availability has been a valid concern for amp makers since the late 1980s, and tubes are now only used in guitar amps, some stereo amps, ham radios and radar applications. While I don’t believe tube manufacturing is totally in danger, the volume of tubes produced per year is nowhere near what it used to be, and is tiny compared to the number of transistors made each year.

• Transistor amplifier manufacturing is easier to automate, not to mention how much easier transistor amps are to package and ship without heavy transformers and little glass bottles.

How Tubes WorkAs discussed in “Chapter Nine—Power Tubes” different tube types affect your amp’s tone differently. Here we’ll discuss the technical pluses and minuses of using one tube type over another.

Grid VoltageWater coming out of your faucet is a great analogy for understanding how grid voltage affects the varying flow of electrons (or current) through a tube (which is exactly why Europeans call vacuum tubes valves”15.1”). Essentially, the control grid in a tube acts like the valve you turn on to operate a water faucet. By controlling how open the valve is, you control the water flowing through the pipe. Similarly, the voltage on the control grid controls how much electrical current flows through the tube.

Circuits are like man-made waterfalls with a pump that takes water from the pool at the bottom of the waterfall and brings it up to the top. In an electrical circuit, the power supply (or battery) is the pump and electrons are the water.

A sealed glass enclosure with all of the air removed (leaving a vacuum) prevents electrons from bouncing into air molecules on their way from the cathode to the plate. When air is present in a tube, electrons hitting air molecules cause the tube to glow blue. A little blue is okay; a lot of blue means your tube is toast, sounds really squishy and needs to be replaced (unless you like really squishy).

DiodesThe most basic tube type is called a diode. A diode has two terminals (hence the di) for current flow and two terminals for the heater. The heater is not part of the diode’s main circuit, but works outside the circuit to make sure the tube’s cathode reaches a temperature hot enough for the tube to operate.

Figure 15.1 Diode

The basic idea behind the diode is to get a piece of metal (usually tungsten which is used in regular light bulbs) hot enough, and then place a second piece of metal close but not touching. The two pieces of metal are connected to a battery (the hot metal connected to minus, the other one connected to plus). When the piece of metal near the heater is hot enough, current flow begins jumping the gap between the two pieces of metal.

The hot piece of metal is called the cathode and the cooler piece is called the anode or plate. Essentially, the high temperature of the cathode “cooks” electrons off the cathode metal similarly to boiling water turning into water vapor. The freed electrons form a cloud around the cathode and sit there. When positive voltage is placed on the plate via the battery, the electron cloud moves toward the plate (opposites attract and electrons are negative).

The electrons move from the plate to the plus terminal of the battery, out the minus terminal in the battery, and back to the cathode. This continuous flow of electrons is essential for a circuit to function properly and is why it is called a circuit. The electrons move around a racetrack-style loop over and over again, never created or destroyed.

The amount of current flowing from the cathode to the plate depends upon the number of Volts the battery makes as well as the construction of the tube itself.

The most important aspect to remember about the diode is that electrons travel in only one direction. All tubes are based upon the concept of the diode, and in all tubes electrons flow from the cathode to the plate.

With other tube types such as triodes and pentodes, manufacturers physically place one or more grids between the cathode and plate to control how many electrons are flowing.

Rectifier TubesRectifier tubes generally have two diodes in one package that uses a common heater and common cathode — simple as that. Rectifiers are rated by how much current each diode is capable of carrying. Higher-current rectifiers produce less power supply sag while lower-current rectifiers produce more.

TriodesA triode is a diode with a control grid (usually just called the grid) placed between the cathode and the plate. A grid is similar to a fish net, not completely blocking all the electrons on their way from the cathode to the plate.

Figure 15.2 Triode

When the voltage on the grid is zero (relative to the cathode), the grid is functionally turned off and electrons flow freely from the cathode to the plate, as with a diode (the opposite to the way a water faucet works; when the faucet is on water flow freely).

When negative voltage is placed on the grid, it decreases the number of electrons flowing from the cathode to the plate (negative grid voltage repels negative electrons), turning down the current flow as you’d turn down a water faucet.

When a constant (DC) negative voltage is placed on the grid along with a varying (AC) voltage, the electron flow between the cathode and the plate varies in step with the AC voltage. The amount of DC voltage first put on the grid is called the bias voltage, and sets the starting point for the tube’s operation.

To Turn a Triode inTo an amplifier (Which is our overall goal):1. A resistor is placed between the battery’s positive terminal and the plate. The voltage on the plate is now

the battery’s voltage minus the resistor’s voltage drop. This voltage is constant (DC) and is dependent upon the battery and the bias (DC) plate current.

When a varying (AC) voltage is added to the grid, for example from your guitar, the plate voltage is equal to the DC plate voltage plus an AC voltage (due to the AC plate current going through the resistor). The AC voltage at the tube’s plate looks just like a bigger version of the AC voltage on the grid.

2. A capacitor is connected to the plate, and the DC voltage on the capacitor’s output side (the side not connected to the plate) is removed, allowing the larger AC voltage to flow onto other circuits.

Voilà! We have a voltage amplifier. The input is the AC voltage on the grid and output is the AC voltage at the output side of the plate capacitor.

Mathematically, the triode is the very best amplifier humans have yet developed.

The problem with triodes as power tubes is that they produce low output power and are inefficient. The amount of current passing through a triode (the plate current) is dependent upon the grid voltage as well as the changing plate voltage (which is really the output of the amplifier). If the plate current could be independent of the plate voltage, a triode could produce much more power.

TetrodesIn the pursuit of higher power, another grid is added between a triode’s control grid and plate that makes the plate current independent of the plate voltage. This second grid is called the screen grid, or simply the screen, and it is what defines a tetrode.

Figure 15.3 Tetrode

The goal of a tetrode is to make the screen tight enough so electrons from the cathode see only the voltage on the screen (which is set to a constant voltage that is approximately equal to the DC plate voltage) and not the voltage on the plate. At the same time, the screen must be physically open enough so that most of the electrons whiz right on through and onto the plate.

The tetrode has four parts — the cathode, the plate, the control grid and the screen grid. Tetra is Greek for four, and is where the tetrode gets its name.

While a tetrode can definitely produce higher power than a triode, a kink in the relationship between the tetrode’s plate voltage and plate current exists. Under certain conditions, some of the electrons reaching the plate bounce off, go backward and become absorbed by the screen. Since the screen is not part of the audio circuit per se, these bounced electrons are lost and reduce the tube’s output power (but not as low as triodes).

PentodesTo eliminate this kink, tube designers add yet another grid, called the suppressor grid, between the screen grid and the plate. Generally connected to the cathode, the suppressor grid is set at zero Volts compared to both the screen and plate, (which are set at high positive voltage). With this relatively very negative voltage, the suppressor grid repels bouncing electrons, forcing them back to the plate.

Figure 15.4 Pentode

The pentode has five parts — the cathode, the plate, the control grid, the screen grid and the suppressor grid. Penta is Greek for five, and is where the pentode gets its name.

This tube type can produce very high gain, high power and high efficiency, and is extremely effective in both preamp and power amp configurations.

The only true power tube pentodes used in guitar amps are EL84s, EL34s and their American equivalents (almost), 6BQ5s and 6CA7s, respectively. Because of their increased gain and wider frequency response, true pentodes sound very different from tetrodes.

Kinkless TetrodesAs you can imagine, a tube becomes more fragile and expensive to manufacture with each additional grid. So tube manufacturers developed a virtual suppressor grid that works without making the physical grid.

Figure 15.5 Kinkless Tetrode

Kinkless tetrodes focus the flow of electrons between the screen grid and the plate. Going back to the water hose analogy, the smaller the hose, the faster the water comes out of the end of the hose. When the electron flow is focused, the sheer pressure of negative electrons creates an extremely negative area in space that repels any electrons bouncing off the plate, like the suppressor grid.

Because the focused beam of electrons makes a pentode — almost — this tube type is also known as a beam pentode. Kinkless tetrodes include 6L6s, 6V6s, 6550s and of course all of the KT power tubes: KT66, KT77, KT88 and KT90.

While kinkless tetrodes are a wonderful idea in theory, in practice they are not quite as effective as real pentodes. Focusing electrons is easier said than done, and the virtual suppressor grid is highly dependent upon how well the flowing electrons are focused. As always in real life, virtual is never quite the same.

What’s in a Name?

each Tube Type has Three designaTions or names:• U.S. civilian name — also known as the RETMA tube designation (for example 12AX7)

• U.S. Military name — also known as the Joint Army Navy or JAN designation (for example 7025)

• European name — also known as the Mullard-Philips tube designation (for example ECC83)

In the past, military spec tubes, such as the 7025, were physically stronger and better made than their civilian counterparts, such as the 12AX7. That distinction is now almost gone.

The U.S. civilian name (also known as the RETMA tube designation) always starts with the tube’s heater voltage. Next, you’ll find one or two letters that were incremented every time one of the manufacturers came out with a new tube design. The final number indicates the number of elements in the tube.

So for example, the 12AX7 dual triode has a 12.6 Volt heater and has seven elements — two plates, two grids, two cathodes and one heater. The 6L6 has a 6.3 Volt heater and has six elements — the plate, beam-forming hardware, screen grid, control grid, cathode, heater (and interestingly, a metal container). 6L6s are actually older versions of the familiar 6L6GC, which comes with a glass container (instead of metal) and is engineering design revision level C.

With European designation for tubes is called the Mullard-Philips tube designation. The first letter indicates the heater voltage (E = 6.3 Volts F=12.6 Volts, and the second letter is the tube type (C = triode, L = power pentode). The optional third letter designates the second tube type (for example a dual triode would have the second and third letters CC). The last two numbers are a simple counter like the letters in the RETMA designation. So, an EL34 is a power pentode with a 6.3 Volt heater, number 34; and an ECC83 has a 6.3 Volt heater with two triodes, number 83.

So, how can a 12AX7 be the same as an ECC83 (which it is) if the ECC83 has a 6.3 Volt heater and the 12AX7 has a 12.6 Volt heater? Both the European and American tubes have split heaters, each half requiring 6.3 Volts that can be connected in parallel or series, requiring the heater supply voltage to be 6.3, or 12.6, respectively.

Note that the KT power tubes do not follow the Mullard-Philips tube designation.

“Appendix B—Power Tubal Tones” has a chart of equivalent tube types with their European and American designations, and some general tonal characteristics based on tube switching experiments using the Ganesha and RG88.

Chapter Fifteen Footnotes

15.1 Europeans also use the classic term anode to describe the part of the tube innards you can see, while Americans call this the plate because of its construction.

I am still amazed, after 35 years of playing the guitar, at how songs can transport me to that exact time in my life, when I first heard or wrote it, while evoking the raw emotion I was feeling then as well. A musical/life snapshot.

What else can do that?

Mike TaborThe Road Apples

www.theroadapples.net

Chapter Sixteen—Safety Basics

0 WARNINGTube amplifiers can be very dangerous and operate at the same voltages as the electric chair (500 Volts). Even though transistor amps operate at much lower voltages (40 Volts), you can still get hurt.

I know some people think, I’ve been zapped with 120 or even 240 Volts AC from the wall and I’m just fine. The problem is that tube amps have high voltage supplies that are often around 500 Volts DC. Since this is only about twice as much as 240 Volts, many players and techs believe they can take it if they get ‘bitten’ now and again while working on an amp.

Scientists have looked closely into the phenomenon of electrocution to determine exactly what happens inside the body. At lower voltages, the body is a rather poor conductor. Because human cells are in a jumbled state, they have a high resistance (electrical current has a difficult time flowing through the jumble). A clear electrical path doesn’t exist as it does with say, copper wire.

However, as current begins to flow through your body, your cells start to line up in a row, dramatically lowering resistance. This lining up can occur very rapidly. Once electricity has created a path through your body, your resistance quickly decreases as the current quickly increases.

Generally speaking, a sustained 100mA (0.1 Amps) will kill you. As little as 10mA can stop your heart and do significant damage to your nervous system and other tissues, like your brain. Note that the electrical current kills you, not the Volts per se. A lot of Volts are needed to get the current started, but once started, the Volts required to sustain a lethal current drop rapidly.

The way people are executed with the electric chair is to knock them out with around 2500 Volts for a couple of seconds, and then hit them with around 500 Volts for an extended period to cause their organs (particularly their hearts) to fail. So grabbing a hold of 500 Volts in your amplifier will give you the shock you need to die without the benefit of first going unconscious.

If you’ve ever been geeky enough to use your Ohmmeter to measure your own personal resistance, you’ll know that it is somewhere in the ten meg Ohms range. Current is Volts divided by Ohms, and 500 Volts divided by ten meg Ohms is 0.05mA. This is a low enough value of current that it may fool you into thinking 500 Volts is okay to grab. So the problem is the nasty lining-up effect, causing your body’s resistance to change with higher voltage. The higher the voltage, the lower your resistance.

As cells line up and the current increases, it begins to explode your cells like little water balloons, causing electrical burns. As the current gets even higher, it can blow apart larger structures in your body, such as your bones and organs and eventually cause you to catch on fire.

If all of these internal explosions aren’t enough to scare you, remember that both your heart and your nervous system (including your brain) are electrical systems. Hitting those systems with random electricity is the equivalent of using defibrillator paddles or giving yourself some memory-cleansing electroshock therapy.

But this isn’t the scariest aspect of the high voltage in tube amplifiers. Tube amp voltage is DC, not AC — and generally speaking, AC wants to throw you and DC wants to stick you.

I was the recipient of around 400 Volts DC once, and experienced the most curious effect of my hand and arm being completely disabled during the shock. Unable to respond to the Let Go Now! signals my brain and nervous system were sending, my hand and arm simply didn’t work. I saved myself by using my legs to walk backward to pull myself off the circuit.

For the remainder of the day, I felt as though I had been on a roller coaster after downing a lot of Tequila (more personal experience), and I was very thankful that my heart hadn’t stopped.

AC voltage isn’t much fun either. During graduate school, an assistant professor was helping wire a building on campus, working with the high voltage AC distribution circuit, which ran at 13,800 Volts (a common distribution voltage at large facilities).

While wiring some step down transformers in a concrete-walled-basement, he accidently took a hold of the 13.8k Volts. Promptly thrown into the air and across the room with such velocity that when he hit the wall some 20 feet away, he was fortunate to only break his arm. And because he was thrown, he was also very fortunate that electricity didn’t actually pass through his body for very long. Thankfully, he wasn’t electrocuted.

My last story is about low voltage DC. I once observed a computer tech attempting to repair an uninterruptible power supply (UPS), which had a good sized 12 Volt battery (about equal in size to two car batteries). When I walked in, he had one of those stout, foot long screwdrivers out and was prying off the cover.

Somehow the screwdriver shorted the battery, ripping the screwdriver out of the tech’s hand, breaking his finger and bending the screwdriver in a 90 degree angle. The spark flash and noise made M-80s seem like sparklers.

Electricity is serious, period. With full respect to the power of electricity, some general guidelines for safety are important when using guitar amplifiers.

imporTanT safeTy guidelines When using a guiTar amplifier:• Periodically wipe off the glass on the preamp and power tubes with a soft clean dry cloth.

Dust and oils from your hand weaken the glass as the tube heats up.

• Always put the Standby Switch in the Off position before turning on your amp, and leave the Standby Switch in the Off position for at least 20 seconds after you have turned on your amp.Tubes need to warm up before they can safely handle the high voltages (300 to 600 Volts) that they normally run. If you turn the Standby Switch On, applying high voltages to the tubes before the tubes are warmed up, you can cause cathode stripping.”16.1”

• Before turning your amp off, put the Standby Switch in the On or Operate position. Leaving the Standby Switch in the On position helps ensure (but does not guarantee) that the electricity in your amp’s filter capacitors will completely drain out when you turn off the amp.

• After several minutes, or before you turn the amp on again, turn the Standby Switch back Off before turning On the Power Switch.

• Power tubes run really hot, so please be careful not to touch them when the amp is on or has recently been on, unless you want to erase your fingerprints.

• Never, ever pull preamp or power amp tubes out of their sockets while the amp is on.

• Never play your amp in the rain on a train, flying a plane, sailing a boat in a moat… or with a goat.

The output of the B+ power supply in tube amps can be anywhere from 300 Volts DC (e.g. an AC 30) to 600 Volts DC (e.g. a Marshall Major or an Ampeg SVT), which is more than enough to hurt you. Please seek professional assistance if your amp is not working properly. But if you ever do find yourself looking at the inside of an amp, practicing the following important safety guidelines can save your life.

folloW These imporTanT safeTy guidelines When Working on a guiTar amplifier:• Never, ever assume that because you turned your amp Off a while ago, that it is safe to go inside.

The power supply capacitors need to be fully discharged before you stick your hands inside a guitar amplifier. If you do not know how to discharge your power supply capacitors, you should not be working on your amp.

• If your circuit is having intermittent problems (such as the sound cutting in and out) perhaps due to a faulty solder joint, use a long, dry, wooden stick, like a chop stick, to tap on the parts to find the problem.Always keep your other hand in your back pocket so you don’t create a path for electricity to go from one hand, across your heart and to the other hand.

• When using a Volt-meter to probe a circuit, always put your free hand in your back pocket.This position breaks the circuit from one hand to the other, removing your heart from harm’s way.

• Do not assume that those trusty Volt-meter leads are your friends until the end of time. Those leads deteriorate and will eventually let you down. Treat yourself to a new set every year or two. You are worth the expense.

A Word About AttenuatorsAttenuators and dummy loads are not electrically the same as speakers. Speakers are inherently low-pass-filter devices and act as something of a shock absorber for your amp. Attenuators and dummy loads are more like running your amp into a brick wall with little or (usually) no shock absorber effect. The end result is that you can get ringing, oscillations or spikes that can cause the output transformer to short out or your power tubes to blow.

Not all attenuators are equal and some cause these problems more than others. A few, but not many amplifiers have internal protections against these problems. So while attenuators are not guaranteed to blow your amp, they are at best very hard on it.

Speakers, Loads and Speaker CableTube amps require some sort of load (while transistor amps do not). Running your amp without a load (a device that dissipates or uses up the power the amp is making), either a speaker or a dummy load, is equivalent to flooring the gas pedal in your car while it is in neutral. All the power the amp makes will be absorbed by the tubes and output transformer, and if you keep it up long enough, your amp will blow the output tubes and/or output transformer, requiring major repairs.

0 WARNINGNever run your tube amp without a speaker or some other load plugged into the speaker output.

Never use guitar cords to connect your amp to your speaker(s), as guitar cords cannot carry the level of Amps that speakers take. This lack of current-carrying capacity causes the guitar cord to internally burn out, which effectively unplugs your speaker(s) from your amp, causing the same problems as running your amp without a load.

In addition, the capacitance of guitar cords causes oscillations or ringing, guaranteeing that guitar cords will burn out your amp the same way attenuators often do.

0 WARNINGAlways use speaker cord to connect your amplifier to your speakers. Other cord types can cause your amplifier to blow.

Chapter Sixteen Footnotes

16.1 Instead of just the electrons boiling off the cathode, the high voltage literally rips entire atoms off a cold cathode, causing permanent damage that eventually leads to lower tube life.

It’s the most rewarding and demanding relationship I’ve had in my life.

JS Deslauriers

Chapter Seventeen—Equipment Grounding

To really understand how to properly ground your equipment, you need to know how electricity gets from the pole in the street to your building, and ultimately, to your gear.

The electricity that comes from the power company is a bit of a mystery to people in general. In North America, we have two different voltages in our houses, (as opposed to Europe’s single voltage system which has traditionally varied from country to country but is standardizing on 230 Volts).

In North America, the voltage coming to your house from the street pole’s transformer is supposed to be 234 Volts AC. In reality, this voltage generally runs a little high, and since 234 Volts is a weird number to remember anyway, everyone calls it 240 Volts. Prior to the 1950s, the voltage coming to your house was 220 Volts, which is why you can still hear someone refer to a 220 Volt outlet.

For safety and other traditional reasons, the entire 240 Volts along with its two halves (120 Volts each) are available to North American homes. Wall outlets in North America are generally wired to be 120 Volts, with the exception of specialized large-load-appliance outlets such as electric clothes dryers, which are wired for the full 240 Volts.

Just as the primary side of the output transformer in a tube amp has a center tap, the street pole transformer’s secondary output side has a center tap that creates the two 120 voltages coming into your house. Tapping is a way of accessing the middle of a transformer winding. So instead of just two wires coming from a transformer winding (one for each end), a center tapped transformer has a third wire connected to the middle of the transformer winding.

If you were to look at the wires coming to your house from the street pole transformer, you would see two wires covered in black insulation, and one bare silvery-looking wire made from aluminum. This wire (silver outside the house; white inside the house) is the transformer’s secondary side center tap, and is connected to ground at the pole.

Because the two black insulated wires are connected to the two ends of the street pole transformer, the difference in voltage between the two black wires coming to your house is always 240AC. Using the waterfall analogy, one wire is the top of the waterfall and the other is the bottom. Whichever you say is which, the difference between the two wires is always 240 Volts relative to each other.

The bare wire coming to your house that is connected to the center tap of the pole transformer winding is analogous to the center of the waterfall. The difference between the middle wire and either of the black wires is always 120 Volts AC, while the difference between the two black wires remains 240 Volts.

The wires from the street pole transformer enter your house and go to your main power panel (Figure 17.1), which is also where the wires from all of your wall outlets go. The bare wire from the pole is connected to the neutral bus (basically a long piece of metal). The neutral bus is connected at one point to the ground bus in the power panel. However, do not think of the neutral bus in your house as ground.

Figure 17.1 Typical Main Power Panel

The two black wires go through the main switch/circuit breaker in the circuit breaker box, and then on to two hot buses (basically two strips of metal behind the smaller circuit breakers).

The main circuit breaker/fuse is the very top large breaker that is separate and different from the other circuit breakers. If you need to turn your entire house off at once, because of say a gas leak or a fire, the main breaker is the way to do it.

For each 120 Volt outlet, you will find one black wire and one white wire. The black outlet wire is hot because it is connected to one of the hot buses through one of the small circuit breakers in the breaker box. The white outlet wire is connected directly to the neutral bus.

For each 240 Volt outlet, you will find two current carrying wires; one black (connected to one of the hot buses through one circuit breaker), the other red (connected to the other hot bus through another circuit breaker).”17.1”

The appliances in your house have one wire connected directly (through circuit breakers/fuses) to one of the black wires coming from the pole transformer. The other appliance wire is directly connected either to the silver bare-center tap wire for 120 Volts, or to the other black pole transformer wire (through circuit breakers/fuses) for 240 Volts.

A neutral and a hot wire (or two hot wires for 240 Volts) for each outlet is all that is needed to run electrical appliances. Houses in North America were wired this way for a long time, which is why old houses have outlet jacks with only two holes in them. Modern electrical codes now require a third wire running through the house that is called and literally connected to the ground.

Let’s get back to your gear. The power plug on your amplifier is connected to the primary side of the amp’s power transformer. The amp’s power transformer does not care which wire is neutral and which is hot, as long as the voltage difference between the two wires is 120 Volts AC.

With vintage and some modern boutique amps, the amp’s chassis is metal and used like one big wire (called chassis ground). So whenever a ground wire is needed, the wire just needs to be connected to the chassis. In fact, one of the two wires coming from the power plug is also connected to the chassis.

The Death SwitchVintage amps produce more or less hum depending on a variety of factors, such as your particular equipment setup, the power coming to your house, the power plug wire a manufacturer chose to connect to chassis ground. To minimize hum, some vintage amps came with a ground switch that allows you to select which power plug wire is used as ground (i.e. connected to the chassis).

The problem with this switch is that the strings on your guitar are also connected to the amp’s chassis ground through your guitar. Depending on the ground switch setting, the chassis is directly connected to either the neutral wire, or to the hot wire from the power panel.

Now let’s say you are playing your guitar while singing into a microphone with a metal case (as most mics have). The microphone also has a connection to the PA system’s chassis ground. Can you guess what will happen when the amp’s ground switch connects the amp’s chassis ground to the opposite wire from the PA system’s chassis ground? 120 Volts applied to your teeth! For this reason, the ground switch is also called the death switch.

The death switch and this entire arrangement is now obsolete and thankfully, illegal. Fender does make vintage reissue amps with ground switches, but the switch is not connected to anything. I personally think they should give up the ground switch and add some external biasing circuitry instead.

While I do not advocate modifying vintage amps, I do advocate disabling the death switch and properly grounding the amp with a three wire plug.

0 WARNINGHave your tech disable a working ground or death switch(es) on your vintage amp(s). Using this switch can cause injury or death by electrocution.

The Ground WireLet’s get back to how AC power works now. The biggest difference between old-fashioned electrical power and modern electrical power is the addition of a ground wire.

In older houses, outlets have two-pronged outlets while newer houses have three-pronged outlets (the original two prongs plus a ground). The ground wire’s purpose is safety and it should never have any electrical current running through it.

The two current-carrying prongs are now different sizes so you know which is neutral and which is hot (the larger is hot). The ground part of the jack is the round hole that looks very different from the two thin slots. In modern amps, the ground wire is (hopefully) connected to the amp’s chassis so everything we touch outside the amp stays at ground voltage.

During the course of normal operation, circuits should behave in the classic two wire scenario with no current flowing through the ground wire. Current should flow through the ground wire only when a fault or problem somewhere in the system occurs. When everything works properly, any current going through the ground wire causes the circuit breaker to trip, disconnecting voltage to the hot wire.

Unfortunately, you can’t always rely on the circuit breaker to shut off the power when your equipment is grounding or shorting out. The current required to get a circuit breaker to trip is usually 20 Amps or more. Situations where the resistance of your body is low (as when you are wet or standing in a puddle) present danger even at 120 Volts — so the ability to turn off the power even when a little current is flowing in the ground wire is essential.

For this reason, the National Electrical Installation Standards (NEIS) now require that all outlets in rooms where a person is likely to be wet must be protected by a ground-fault circuit interrupter (GFCI), sometimes called a ground fault interrupter (GFI). A GFCI is essentially a circuit breaker that disconnects the hot wire from the outlet, just like a regular circuit breaker does.

The difference is that a regular circuit breaker trips when a preset limit in the hot wire’s current is reached (for example 20 Amps). A GFCI trips when even a tiny amount of current (4 to 8mA or milliamperes or 1/1000th of an Amp) flows through the ground wire, or when a mismatch between the current flowing through the hot wire and the neutral wire of more than 8mA occurs, (the reason for tripping at a mismatch is that some of the extra current flowing out of the hot wire can flow through you before going to ground).

One GFCI at the beginning of a run of outlets protects all the outlets on the run.

To take advantage of all these modern electrical protection methods, a guitar amp’s ground wire must be solidly connected to the chassis at some point, so your guitar strings are always at ground potential and you aren’t in danger of shock. Neither the hot wire nor the neutral wires coming from the power plug should be connected to the chassis, either directly or indirectly through a capacitor (as with the death switch).

0 WARNINGNever use a three-wire-to-two-wire converter to get your modern amp to work in an old house. This is just too dangerous — go practice somewhere else.

After all of this discussion about the need to have a chassis ground and a third ground wire on your plugs, you may rightfully ask why you can still purchase appliances, like lamps or vacuum cleaners with only two pronged plugs.

A class of appliances called double-insulated is allowed to leave out the ground wire because no single electrical failure on these appliances could cause the user to come in contact with the wall voltage. These appliances come

with literally two distinct layers of insulation, which would require a very serious failure for you to get shocked. Please note, however, that double insulated guitar amplifiers do not exist. Never use a two-pronged plug with a guitar amp.

0 WARNINGIf you have an amplifier with a two-pronged plug, have your tech add a ground wire before turning the amp on.

The ground wire is your best bet for not being severely electrocuted in case of a catastrophic failure inside your amp.

Chapter Seventeen Footnotes

17.1 These two circuit breakers are generally physically connected to each other into a double circuit breaker. The reason the double circuit breaker works is that the hot buses physically alternate in the circuit breaker part of the power panel. The top left circuit breaker is on one hot bus, the second breaker down in the left is on the other hot bus and so on.

Part Four—Appendices

a | “appendix a—speaker Ohm Charts”

B | “”

C | “appendix C—preamp tuBe tYpes”

d | “appendix d—ampliFier BlOCk diaGrams”

Appendix A—Speaker Ohm Charts

The following charts show the Ohms settings to use when connecting two speakers, using either Series or Parallel connections. The OHMS Exact column shows the ideal amplifier impedance setting for that speaker pair — set your amplifier’s impedance to the closest setting available.

The WATTS columns show the number of Watts being delivered to each speaker for each configuration.

0 WARNINGExceeding the power rating for an individual speaker will cause it to blow.

30 Watt AmplifierTwo Series Speakers Connected to a 30 Watt amplifier

OHMS speaker 1

OHMS speaker 2

OHMS exact

WATTS speaker 1

WATTSspeaker 2

4 4 8 15 15

8 8 16 15 15

16 16 32 15 15

4 8 12 10 20

8 16 24 10 20

4 16 20 6 24

30 Watt Amplifier Two Parallel Speakers Connected to a 30 Watt amplifier

OHMS speaker 1

OHMS speaker 2

OHMS exact

WATTS speaker 1

WATTSspeaker 2

4 4 2 15 15

8 8 4 15 15

16 16 8 15 15

4 8 2.7 20 10

8 16 5.3 20 10

4 16 3.2 24 6


OHMS speaker 1

OHMS speaker 2

OHMS exact

WATTS speaker 1

WATTSspeaker 2

4 4 8 25 25

8 8 16 25 25

16 16 32 25 25

4 8 12 16.7 33.3

8 16 24 16.7 33.3

4 16 20 10 40

50 Watt Amplifier Two Parallel Speakers Connected to a 50 Watt amplifier


OHMS speaker 1

OHMS speaker 2

OHMS exact

WATTS speaker 1

WATTSspeaker 2

4 4 8 50 50

8 8 16 50 50

16 16 32 50 50

4 8 12 33.3 66.7

8 16 24 33.3 66.7

4 16 20 20 80

100 Watt Amplifier Two Parallel Speakers Connected to a 100 Watt amplifier.

OHMS speaker 1

OHMS speaker 2

OHMS exact

WATTS speaker 1

WATTSspeaker 2

4 4 2 50 50

8 8 4 50 50

16 16 8 50 50

4 8 2.7 66.7 33.3

8 16 5.3 66.7 33.3

4 16 3.2 80 20

Appendix B—Power Tubal Tones

Replacing power tubes is an essential routine maintenance procedure with all tube amplifiers. A working musician will need a new set of power tubes every six months or so.

Changing the type of power tube can have a very dramatic effect on your amp’s tone, so don’t be afraid to experiment. Refer to your amplifier’s instruction manual for tube switching and biasing capabilities.

0 WARNINGIf your amp is not cathode biased (self-biasing), and does not offer an external biasing feature, it needs to be taken to your tech for a power tube change. Adjusting bias currents involves measuring lethal high voltages. For internal bias amps, have your tech change your power tubes for you.

Tube Tone Characteristics

TUBEnaMe

GAIN

BANDWIDTH

CLEANsound

DISTORTEDsound

6L6 5881

Fairly

low

Mid range emphasis

Warm Smooth

6V6 Similar to 6L6 but w/less power

Mid range emphasis

Warm to swampy (depending on mfg)

Warm to high end bite

EL34 6CA7

Highest gain of octal power tubes

Wide Bandwidth w/ extended highs & lows

Crystalline, articulate

Crunchy moving to creamy w/more drive

EL84 6BQ5

Highest gain of all power tubes

Wide Bandwidth w/ extended highs & lows

Articulate, chimey

Crunchy w/ a bit of high end snarl

KT66 Slightly more gain than a 6L6

Midrange emphasis w/ more highs and lows than a 6L6

Warm w/ some nice high end

Mildly crunchy to smooth

KT77 Slightly less gain than an EL34

Similar to EL34 w/ slightly rolled-off highs

Warm & articulate

Some crunch to smooth

KT88 Low gain Similar to KT77 but with more low end emphasis

Warm yet mildly sterile

Punchy, needs lots of drive to breakup

6550

Low gain

Similar to KT88 w/ less high end

A little sterile

Punchy, needs lots of drive, a little bass heavy

Tube Substitution Chart

TUBE naMe

TUBEtype

SUBSTITUTESacceptable”b.1”

6L6 5881 Beam Pentode EL34 KT66 KT77 KT88 6550”B.2”

6V6 Beam Pentode 6L6 EL34 KT66 KT77 KT88 6550”B.3”

EL34 6CA7 True Pentode 6L6 KT66 KT77 KT88 6550

EL84 6BQ5 True Pentode None

KT66 Beam Pentode 6L6 EL34 KT77 KT88 6550



6550 Beam Pentode 6L6 EL34 KT66 KT77 KT88

Appendix B Footnotes

B.1 Check with your tech to make sure your amp is configured properly for tube substitution and proper bias current values.

B.2 If the amp’s high voltage supply (aka B+) is less than 425 Volts, a 6V6 can be substituted for other octal tubes (6L6, EL34, KT66, KT77, KT88, 6550, etc.) assuming the amplifier’s bias adjustment has a wide enough range.

B.3 A low power amp designed for 6V6s will be severely stressed by using higher power tubes, but should be okay.

Appendix C—Preamp Tube Types

Preamp tubes vary widely depending on the manufacturer and model. 12AX7s in particular have a wide variety of models to choose from.

The following chart is a guideline for general preamp tube characteristics. Please consult your tech for info on the latest and greatest varieties.

Preamp Tube Types

TUBE naMe

GAINleVel relatiVe

POWER handling capacity(Watts)

SUBSTITUTESacceptable

EUROPEAN &Military equiValents

Hot 12AX7 100% 1.2 Any

12AX7 12AY7

12AT7 12AU7

12AX7A ECC83 7025 ECC803S CV4004 E83CC

Low Gain 12AX7

80% 1.2 Any

12AX7 12AY7

12AT7 12AU7

12AX7A ECC83 7025 ECC803S CV4004 E83CC

5751 Special Mil Spec 12AX7

70% 1.2 Any

12AX7 12AY7

12AT7 12AU7

ECC83 7025

12AT7 60% 2.5 12AU7 ECC81 6021 CV455 CV4024

A2900 CV455

12AY7 44% 1.5 Any

12AX7 12AY7

12AT7 12AU7

6072 6072A

12AU7

20%

2.75

12AT7

12AU7A ECC82 ECC802S CV4003 E82CC 5814A

Appendix D—Amplifier Block Diagrams

The block diagrams on the next two pages show the signal flows for a non-specific vintage amplifier and modern two channel amplifier with bells and whistles. Your amp may or may not have all of the components shown here.

The Modern Amplifier Block Diagram does not include the Bias and Heater Supply signal paths. Because these power supply components are identical for both amp configurations, please refer to the Vintage Amplifier Block Diagram.

Figure D.1 Vintage Amplifier Block Diagram

Figure D.2 Modern Amplifier Block Diagram

Checklists and Glossaries

CheCklist a | “CheCklist a—ChOOsinG an amp”

CheCklist B | “CheCklist B—saFetY Guidelines”

GlOssarY a | “GlOssarY a—teChniCal”

GlOssarY B | “GlOssarY B—tOnal”

Checklist A—Choosing an Amp

Personal Considerations• Do I need this amp for a wide variety of tones, or can I afford to get different amps for different tones?

• Am I going to gig with this amp? If so, does the band’s PA allow me to mic my amp?

• How loud is my drummer?

• How loudly can I, or do I want to, play in my normal practice space?

Amp Specific Questions• Is the amp excessively noisy?

• Does the amp have good string-to-string articulation when played both clean and distorted? Can I hear each individual string or do chords just turn to a roaring mush? Does the amp engage me and make me want to play?

• Does the amp fart out at the low end when pushed?

• Does the amp take pedals well?

• Does the amp respond to my touch or does it feel like I’m playing a keyboard?

• Does the amp sound good with both humbuckers and single coil pickups?

• Does turning the amp’s tone controls actually do something?

• Is the amp excessively buzzy when distorted?

• Are the amp’s power tubes self-biasing/cathode-bias or fixed-bias?

• If the power tubes are fixed-bias, does the amp offer an external bias feature so I can measure and change the bias current without taking the amp apart?

For more information on these important considerations, please read “Chapter One—A Good Amp”

Checklist B—Safety Guidelines

Safety Guidelines Playing Your Amp• Periodically wipe off the glass on the preamp and power tubes with a soft clean dry cloth. Dust and

oils from your hand weaken the glass as the tube heats up.

• Always put the Standby Switch in the Off position before turning on your amp, and leave the Standby Switch in the Off position for at least 20 seconds after you have turned on your amp.

• Before turning your amp off, put the Standby Switch in the On or Operate position.

• After several minutes, or before you turn the amp on again, turn the Standby Switch back Off before turning on the Power Switch.

• Power tubes run really hot, so please be careful not to touch them when the amp is on or has recently been on, unless you want to erase your fingerprints.

• Never, ever pull preamp or power amp tubes out of their sockets while the amp is on.

• Never play your amp in the rain, on a train, flying a plane or in vain; sailing a boat in a moat with a tin coat… or with a goat.

Safety Guidelines Working on Your Amp 0 WARNING

Tube amplifiers operate at the same voltage as the electric chair (500 Volts) and can be very dangerous. Even though transistor amps operate at much lower voltage (40 Volts), you can still get hurt. Please use caution and always follow these safety guidelines.

• Never, ever assume that because you turned your amp off a while ago, that it is safe to go inside; the filter capacitors may be holding lethal voltages.

• If your circuit is having intermittent problems (such as the sound cutting in and out) perhaps due to a faulty solder joint, use a long, dry, wooden stick, like a chop stick, to tap on the parts to find the problem.

• When using a Volt-meter to probe a circuit, always put your free hand in your back pocket.

• Do not assume that those trusty Volt-meter leads are your friends for the rest of time. Replace them at least once a year.

For more information on these important safety guidelines, please read “Chapter Sixteen—Safety Basics”

Enjoy your gear, but please always use caution and play safely!

Glossary A—Technical

AC or alternating current Voltage that varies between zero and a maximum or peak voltage, and goes back down again to zero;

then goes down to a minimum negative peak voltage and returns back to zero to start the entire cycle over. The number of times a voltage waveform repeats in one second is called the frequency and is measured in Hertz.

beam power tube or beam pentode See kinkless tetrode.

BJT or bipolar junction transistor The original transistor type, a BJT behaves less like a tube than any other transistor.

capacitor A circuit element measured in Farads, usually microFarads (uF) or picoFarads (pF), that allows only AC current/voltage to pass — not DC current or voltage.

Capacitors block DC voltage so one side of the capacitor can have a very high DC voltage and the other side can be at zero Volts DC. Consisting of two conductors separated by an insulator, a capacitor allows high frequencies to pass right through, increasingly blocking AC as the frequency gets lower.

choke See inductor.

coil See inductor.

conductor A material that allows electricity to easily flow through it — for example a metal wire.

cone The largest part of a speaker moved by the voice coil. The cone is used to push and pull air, which creates sound.

core The material inside the windings (or coil) of an inductor or transformer. The core can be air (as in speakers) or easily magnetized material such as iron (as in chokes and transformers).

crossover distortion An extremely nasty distortion that occurs when the output tubes are biased too cold.

DC or direct current Voltage that does not vary and is always the same. The voltage produced by the your car’s battery is (for

the most part) always 12 Volts. All amplifiers use one or more DC voltage power supplies to run and bias the tubes.

diode A diode is a circuit element that allows current to flow in only one direction. Diodes are typically used to make rectifier circuits, and can be tube or solid state. Solid state diodes are like a perfect on/off current-flow switch. Tube rectifiers are like a perfect switch with a fairly large resistance.

discrete device A single device, for example, a resistor, transistor or tube (as opposed to an IC chip that has many

devices on it).

electrolytic capacitor A capacitor that has an electrolytic insulator between two conductors. Electrolytic insulators can hold

more charge (with a higher capacitance rating in Farads), and withstand a much higher voltage in a smaller space than other insulators. Electrolytic capacitors are best used in power supply applications as opposed to audio signal path applications.

FET or field effect transistor A transistor that behaves more like a tube than a BJT (bipolar junction transistor).

filter capacitor A large, usually electrolytic capacitor used to smooth out the ripples (bumps) in power supplies, causing

the power going to the amplifier to behave more like perfect DC.

frequency Frequency is measured in Hertz (Hz), or in old literature, Cycles Per Second (cps). On a repeating (or AC) waveform, frequency is the number of times the repeating waveform completes a cycle in one second.

germanium An older semiconducting material used before silicon became the dominate semiconductor. Germanium transistors and diodes have unique distortion and clipping characteristics that make them desirable for guitar-effects pedal use.

ground or earth The point in a circuit that is at zero AC and DC Volts. The ground is usually connected through the

house wiring to a stake in the earth outside the house/building.

headroom The amount of power an amplifier can produce above and beyond its rated power.

impedance With DC voltages, impedance is identical to resistance. With AC voltages, resistance along with other factors come into play, limiting a circuit’s current flow. The sum of all the factors that limit the flow of current is called impedance.

impedance selector An impedance selector switch allows you to choose how the output transformer is connected to the

speaker outputs to achieve the amp’s optimal (or not) output power. Typically you can select between four, eight or 16 Ohms.

inductor A circuit element measured in Henries (H) that allows DC to pass through, but increasingly blocks AC as the frequency goes higher. Inductors are used in high-end filtering circuits like graphic equalizers or as power supply filtering elements. A transformer is a set of two or more inductors sharing a magnetic core.

insulator A material that does not conduct (or let pass) electricity. Insulators are often used to coat wires to protect people and equipment from inadvertently coming in contact with electricity carried by the inner wire.

integrated circuit (IC) A solid state circuit consisting of transistors, resistors and capacitors. An IC can contain tens to millions

of components depending on the circuit.

jack A jack is a female receptacle that you put a plug into. The receptacle where you plug your guitar into your amp is called the Input Jack.

JFET or junction field effect transistor An early type of FET with characteristics similar to a MOSFET, most commonly used as a solid state

switch.

kinkless tetrode A vacuum tube amplifying device containing four (tetra) elements with a virtual fifth element. A

kinkless tetrode simulates a pentode.

knob A knob is a handle connected to a Potentiometer (Pot). The knob is used to make turning the pot easy and helps makes the amp more attractive.

MOSFET or metal oxide semiconductor field effect transistor The transistor type that behaves most like a tube (specifically a Pentode).

negative feedback An engineering term for a circuit that reduces distortion by comparing the circuit’s output to its input.

The price of distortion reduction is a reduction in gain.

opamp or operational amplifier An extremely high-gain but not necessarily high-quality IC amplifier. The overall gain and other

parameters are defined by external resistors and capacitors that comprise an opamp circuit.

OPT or output transformer Connects the power tubes to the speakers. Has one primary winding that is usually shared half-and-

half with each set of power tubes. The secondary winding is connected to the speaker output of the amplifier.

parallel connection Two electrical devices are connected in parallel when the current flowing to the combination can go into

the input of either device. For example, two water hoses connected together at the spigot”7.1.”, allowing flow to either or both hoses is a parallel connection.

passive components or passives Electronic components that do not amplify voltage or current; generally refers to resistors, capacitors

and inductors.

pentode A vacuum tube amplifying device with five (penta) elements.

PI or phase inverter A circuit that produces two out-of-phase signals; with one signal going up and the other going down. On

push-pull amplifiers (which is most amplifiers), the two (or two sets) of power tubes (or transistors) each require inputs that are exactly 180 degrees out-of-phase with each other.

plug The male part of a guitar cable that you put into a jack, either on your guitar or your amplifier.

positive feedback An engineering term for a circuit that almost uncontrollably creates louder and louder volume by

feeding the system’s output back to the input. Placing your guitar in front of your speakers while your amp is cranked causes positive feedback.

pot or potentiometer A variable resistor with two ends and a center wiper connection that is mechanically varied by turning.

Pots almost always have a knob connected to them to make turning easy. Unsealed pots can develop dirty wipers that need to be cleaned with lubricated contact cleaner.

power supply sag The phenomenon where the more power the amplifier requests from the power supply, the lower the

voltage the power supply creates. A great example is turning on your car lights before starting your car; when you turn the ignition key to start the car, the lights dim. This dimming is caused by the starter motor taking so much current from the battery that the battery voltage drops (or sags).

PT or power transformer Part of the power supply that (depending on the amp), turns the 120 Volts AC wall voltage into high

voltage AC, which is used by the remaining parts of the power supply to make the high voltage DC required by the tubes. The power transformer also creates the low AC voltage required by the tube heaters, bias circuitry, etc.

primary winding A coil of wire used as the transformer’s input.

rectifier A circuit arrangement with two or more diodes that takes an AC voltage and flips the negative half into positive voltage. A rectifier’s output can be thought of as a series of positive bumps that are smoothed out via filter capacitors into one relatively constant DC (or flat) voltage.

resistor A circuit element (measured in Ohms) that allows both AC and DC current to pass in a controlled or restricted manner. The voltage on one end of the device is equal to the voltage on the other end, plus the current going through it, times the resistance. The equation for a resistor is:

Voltage at one end = Voltage at the other end + (Resistance × Current)

RMS or root mean squared Because it doesn’t vary, DC voltage is easy to measure (for example, your car battery is always 12

Volts). AC voltage varies and is trickier to measure. Because the waveform is positive half the time and negative the other half, simply averaging the AC voltage results in zero Volts. RMS is a mathematical formula used to measure the strength of the AC voltage with the goal of producing a number equivalent to a DC voltage.

For example, a light bulb connected to 120 Volts DC shines just as brightly as a light bulb connected to 120 Volts RMS AC. When people discuss AC voltage, they are almost always referring to the RMS

value of the AC waveform.

secondary winding One or more windings or coils of wire used as a transformer’s output.

semiconductor A solid material that does not fully conduct (like copper does) nor does it fully insulate (like plastic

does). Electrons can flow through a semiconductor but only with help (which is the job of a transistor). Common semiconductor materials include germanium, silicon and gallium-arsenide.

series connection Two electrical devices are connected in series when current flowing into the first device and back out

again is directed to the second device and out again. For example, two water hoses connected together with one end of the double hose connected to a spigot is a series connection.

solid state Refers to the use of transistors to control the flow of electrons through a semiconductor. Vacuum tubes control the flow of electrons through a vacuum. Solid state is the opposite of vacuum state.

tetrode A vacuum tube amplifying device with four (tetra) elements.

tone stack An amplifier’s circuitry, including the pots, associated with most Bass, Mid and Treble controls. A tone stack tends to look like a stack of pots connected to each other through various resistors and capacitors.

transformer A circuit component with one input and one or more outputs. The input and each output are coils of wire wrapped around a shared iron core. AC current in the input coil creates a magnetic field in the iron core. The magnetic field in the core creates AC current in the output coils. Each output voltage is related to the input voltage via the number of turns of wire in each coil.

transistor A three terminal device that can be thought of much like a triode tube, but behaves more like a pentode in its current flow characteristics. A transistor is used to control the electron flow through a solid semiconductor such as silicon or germanium.

triode A vacuum tube amplifying device with three (tri) elements. The current flow between two of the elements is controlled by the voltage on the third element.

tube A device used to control the flow of electrons through a vacuum, often called a vacuum tube.

tube socket The ceramic or plastic socket you plug a tube into. The socket holes contain hollow metal sleeves that accept the tube’s pins.

valve European name for a vacuum tube.

voice coil The coil of wire (or inductor) in a speaker. The AC current produced by the amplifier is connected directly to the voice coil. The coil is wrapped around a voice coil former which is then connected to the cone. The current in the coil creates a magnetic field that interacts with the magnetic field created by the speaker’s permanent magnet, forcing the coil to move.

Glossary B—Tonal

articulate The amp is responsive to your touch and the tone of your guitar, producing a clear sound, even when the amp is overdriven or distorting.

bright Accentuated treble.

bucket of bees Distortion that is less than smooth. A lot of unwanted fuzz surrounding the notes, taking away clarity

and punch.

buzzy See bucket of bees.

chimey Nice bright, sparkley high end. Examples can be found in Vox AC30s or Fender Blackface amps.

clean Very little overdrive or distortion.

compressed The amp squishes the overall volume and distortion on each note. Notes sound relatively the same

regardless of how hard or soft you pick them.

dark Lacking treble.

dimebag No, not drugs. Refers to Dimebag Daryl’s tone choice of diming (turning all the way up) the Bass and Treble knobs to ten and bagging (turning all the way down) the Mid knob — a surefire recipe for classic metal sounds as long as your Mid control offers the required range.

distortion Generally associated with amps that sport a master volume and have more gain, distortion has a more modified tone than simple overdrive. For example, Led Zeppelin generally has an overdriven tone, while Korn has a distorted tone.

fat Thick or having a lot of Bass and/or Midrange.

flabby Generally refers to the low end being less than punchy or tight.

flatulent or farty Overly flabby — when the low end is completely out of control and creates a farty sound.

growl A deep, throaty distortion as opposed to a screaming high end.

hair As in a little hair on the note meaning just a bit of distortion on an otherwise clean note.

honky Overly accentuated midrange.

ice pick in the forehead Piercing high end that literally makes you feel as if you have an ice pick in your forehead.

knob twiddler A player who spends more time tweaking the knobs on his amp than actually playing his guitar.

Marshally Generally speaking, a relatively tight, punchy sound with a pronounced upper midrange, tight low end and good articulation.

overdrive Increasing the guitar signal going to the amplifier so the preamp, power amp and/or speakers are pushed from linear (clean) to non-linear (dirty) behavior.

punchy Immediate, tight response from the amp.

raunchy An old-school type distortion, such as old blues or early rock ’n roll (Muddy Waters is a great example).

saggy A delayed, mushy response with high end roll off.

smooth The opposite of punchy; a mellower less in-your-face response.

sterile Tone that is lacking character, as if you plugged directly into a mixing board or stereo.

string definition Ability to hear each string in a chord, even when the amp is distorting.

suck knob (As in Please Turn Down The… ) References a Far Side Comic with a mixing board featuring a Suck knob.

thin The opposite of fat, generally lacking Bass and lower Mids.

tight An amp that tracks your playing exactly. The opposite of saggy.

touch responsive An amp that responds to your individual pick attack technique with changes in tone and response (or

feel).

touch sensitive An amp that responds pretty much the same regardless of the pick technique you use. Because lightly

touching the strings creates the same high gain distortion as strumming, touch sensitive often refers to high gain. The opposite of touch responsive.

transistory Tone that is thin, sterile, buzzy.

tweedy An amp that responds with the saggy, swampy, wild tone characteristic of Fender Tweed amps.

About the Author

Dave Zimmerman graduated with honors from the University of Washington in 1994 with a Masters of Science in Electrical Engineering. His thesis involved analog circuit design using chaos theory, and Dave has been applying nonlinear analysis to award winning electronics and environmental software design for Fortune 500 companies ever since. As the founder of Maven Peal Instruments, he hand-wired over 1,000 amplifiers sporting a new power supply design called the Sag Circuit.

Ever been stuck at a gig or practice session with unwanted hiss, ghost notes, muddy, harsh or trebly tone? How about squealing or hissing? Buzzing or ringing? Tremolo or reverb trouble? Rattling or vibrating? The Guitar Amplifier Player’s Troubleshooting Guide is the definitive source for fast answers to your guitar amplifier troubles. Written by award-winning amp designer Dave Zimmerman of Maven Peal, author of The Guitar Amplifier Player’s Guide, the Troubleshooting Guide arms you with the info you need to quickly and effectively take on whatever problems you encounter, in whatever spot you’re in.

http://www.amazon.com/Guitar-Amplifier-Players-Troubleshooting-Guide-ebook/dp/B009FMM2V4/ref=sr_1_2?ie=UTF8&qid=1428565214&sr=8-2&keywords=guitar+amplifier+player%27s+guide+zimmerman

http://www.amazon.com/Guitar-Amplifier-Players-Troubleshooting-Guide-ebook/dp/B009FMM2V4/ref=sr_1_2?ie=UTF8&qid=1428565214&sr=8-2&keywords=guitar+amplifier+player%27s+guide+zimmerman

the guitar amplifier player_s guide - dave zimmerman

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