PSU-1848/2448 Power Supply KitRegulated Split Power SupplyWith +48V Phantom Power

Simplicity Counts, Detail Matters.

No part of this document may be reproduced, either mechanically or electronically, posted online on the Internet, inwhole or in part, without the expressed, written permission of FiveFish Studios. This document is solely provided

to the kit builder of the PSU-1848/2448 Power Supply Kit.

Copyright 2007 FiveFish Studioswww.fivefishstudios.com

Last Update: 12/21/07

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PSU-1848/2448 KITPower Supply for the SC-1 Mic Preamp Kitand other OpAmp, InAmp based projects

Assembly Guide Rev 4.0

This is a split power supply designed to give positive and negative voltages and +48V phantom power. It has a small form factor,measuring only 3.5” (W) x 1.9” (H). The PCB is professionally manufactured, with double-sided copper, plated-through holes,and top silkscreen component labels. This is designed to work with the SC-1 Mic Preamp Kit, or any opamp preamp project.

Specs: Regulated Voltages Output Range (using PWR-TRAFO kit transformer)Output 1: 20 Volts to 48+ Volts Output 2: 1.2 Volts to 21+ Volts (up to 25+ Volts for PSU-2448 mod)Output 3: -1.2 Volts to -21+ Volts (up to 25+ Volts for PSU-2448 mod)

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A power transformer is required. DO NOT CONNECT THE 110/220 AC LINES DIRECTLY TO THE PCB.

For this discussion, I'm assuming you're using the 1U or 2U PWR-TRAFO kit that I'm selling.

STOP! READ THE DIRECTIONS BELOW:First, determine which power transformer kit you have. I supply (2) kinds of Power Transformer Kits. Look at the photos below.

If you are using a different brand/model of transformer, please consult the manufacturer for their documentation.

1U PWR-TRAFO KIT 2U PWR-TRAFO KIT

USING THE 1U PWR-TRAFO KIT TRANSFORMER(photo shown above)

110 VOLT OPERATION

For 110V operation, we need to connect the primaries in parallel.

Connect the BLUE and VIOLET wires together.

Connect the GRAY and BROWN wires together.

Connect both across the 110V line.

USING THE 2U PWR-TRAFO KIT TRANSFORMER(photo shown above)

110 VOLT OPERATION

For 110V operation, we need to connect the 2 primaries inparallel.

Connect the (2) RED wires together and connect the (2) BLACKwires together.

110V is applied across the RED and BLACK wire.

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220 VOLT OPERATION

For 220V operation, we need to connect the 2 primaries in series.

Connect the GRAY and VIOLET wires together.

220V is applied across the BLUE and BROWN wires.

220 VOLT OPERATION

For 220V operation, we need to connect the 2 primaries inseries.

Connect the RED and BLACK wire together (that are beside eachother… see diagram above).

220V is applied across the outer RED and BLACK wires... (seediagram above)

For Both 110V or 220V OPERATION

On the secondary side, we need to connect the RED and ORANGEtogether. (this will be the center-tap wire CT). The center-tap wirewill connect to the CT pad on the PCB.

Connect the BLACK wire to AC1 on PSU PCB.

Connect the YELLOW wire to AC2 on PSU PCB.

For Both 110V or 220V OPERATION

On the secondary side, we need to connect the BLUE and GREENwires that are beside each other. (see diagram above…this willbe the center-tap wire CT). The center-tap wire will connect tothe CT pad on the PCB.

Connect BLUE wire to AC1 on PSU PCB.

Connect the GREEN WIRE to AC2 on PSU PCB.

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Circuit Operation:

RECT1 is a bridge rectifier for the 48V section that converts the input AC voltage to DC. C1 and C2 is a filter capacitor that filtersthe ripple voltage after the rectifier.

This filtered DC voltage then goes to IC1, which is a 3-terminal adjustable voltage regulator. The values for R1, R2 and R3 arechosen so that you can achieve a +48V output. R3 is a trimmer resistor that is used for fine-tuning the output voltage.

D1 and D2 are diodes that protect the IC1 voltage regulator. C3 is added for stability, along with bypass capacitors C4 and C5.C18 is another filter capacitor to further reduce ripple from the 48V section. Since the 48V output will be used for phantompower, we want it to be as clean as possible to prevent the mic preamp from amplifying any ripple/hum in the supply.

RECT2 is another bridge rectifier for the split supply section. C8, C9 are filter capacitors to smoothen out the ripple. C10 andC11 are bypass capacitors, along with C12, C13, C14 and C15. IC2 is a positive 3 terminal voltage regulator while IC3 is it’scounterpart negative 3 terminal voltage regulator. D3, D4, D5, and D6 are protection diodes for the regulator.

Resistor values R4, R5 are chosen so IC2 and IC3 (along with resistors R6 and R7) will supply +/-18Volts. R6 and R7 are trimmerresistors used for adjusting the output voltage.

Resistors R8 and R9 are current limiting resistors for LED1 and LED2. You can solder LEDs to the PCB as a visual reminder if theboard is powered up. Or, you can to mount your LEDs to your front panel as a visual indicator for the (+) and (-) supply voltage.

Basic Tools RequiredA few basic tools are required to build this kit.

1. Soldering iron – adjustable temperature recommended, but not necessary. Your soldering iron must have a sharpconical tip. I do not recommend a “flat-head, screwdriver-type” soldering iron. DO NOT USE A SOLDERING GUN. Theyare usually rated at 100Watts and are overkill for this project.

2. Mini Pliers Cutter – to cut component leads, wires, strip insulation off wires (if you don’t have a wire-stripper tool).

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3. Mini Long Nose Pliers – to bend component leads, use as a heatsink, hold components, tighten bolts.

4. Manual Solder sucker pump – sucks up solder when you made a mistake soldering components on the PCB. Primitiveoperation, but it works… kind of.

5. Multitester – A simple meter/tester to measure resistance, and voltages. A digital read-out is a big help.

6. Soldering Lead – 60/40 lead or lead-free solder

7. Magnifying glass – to see what you’re doing!

8. Clean and well-lighted work area – Lots of good lighting, clean work area. You want to be able to leave your work-in-progress without packing everything away.

Extra Tools (Nice to have, but not required)

1. Vacuum desoldering pump – if you make a mistake, you need to pull out the component from the PCB2. Component lead bender – bend component leads like resistors uniformly and evenly3. PanaVise – to hold PCB while you’re working on it4. Tweezers – to pick tiny things5. Masking tape – to hold components on the PCB while working6. Wire-stripper – for cutting wires and stripping its insulation

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PSU-1848/2448 Assembly Guide

Follow these instructions to assemble your PSU-1848 Power Supply. Bend the component leads like the photo shown belowbefore inserting them to the PCB. For diodes, allot a small clearance before bending the leads.

Step 1. Solder all resistors and diodes to the PCB. (R1, R2, R4, R5, R8, R9)

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White band of diode is oriented on top.

Step 2. Solder all ceramic capacitors to the PCB. These are the small yellow components. (C2, C5, C10, C11, C12, C13)

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Step 3. Solder the bridge rectifiers, RECT1 and RECT2. These are the small circular components that have a “chopped-off” side.Note the proper orientation. Follow the guide printed on the PCB.

Step 4. Solder LED1 and LED2. (Note: You may wire instead LED2 to a front panel LED indicator lamp, or use the LED that comesin the Power-Transformer Kit). The LONG LEG of the LED should be inserted at the bottom hole.

Step 5. Solder all small electrolytic capacitors. (C3, C4, C14, C15, C16, C17)

Step 6. Solder the trimmer resistors, R3, R6, R7. Note orientation of trimmer resistors.

Step 7. Solder the medium sized capacitors C6, C7.

Step 8. Solder capacitors C8, C9.

Step 9. Solder capacitors, C1 and C18. These are snap-in type capacitors. You may need to do a slight twising motion wheninserting it into the holes.

Step 10. Solder voltage regulators IC1, IC2, IC3. For aesthetic reasons, keep all their height at the same level. The flat side (i.e.metal side) of the regulators should be facing out towards the top edge of the PCB.

Step 11. Install TO-220 heatsinks to your regulators. Use small nut and bolts to fasten the heatsinks to the regulators. You don’tneed to install insulators. Just make sure the 3 heatsinks do not touch each other, or the metal part of your case.

Step 12. Wire the PCB to your power transformers. See the PSU-1848 Wiring Guide below.

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PSU-1848/2448 Wiring Guide

1. Connect AC1, AC2 and CT pads of the PCB to the secondary windings of your power transformer.2. Connect the (+), (-) and GND to your SC-1 Preamp, or project.3. Connect the +48V pad to your SC-1 Preamp +48V pad.

Note: Before connecting the power supply outputs directly to your project, measure the output voltages first and adjust ifnecessary. See the section Voltage Adjustment Guide below.

PSU-1848/2448 Voltage Adjustment GuideWhen calibrating/adjusting the output voltage of the PSU-1848/2448, make sure there is a "load" connected to the PSU board.Otherwise, you may get a false reading when turning the trimmer pot.

The simplest way to do this is to just solder the (2) on-board LEDS on the PSU-1848 board.

1. Using a voltmeter, measure the voltage across the (+48) and GND terminals. We want a voltage reading of +48Volts if you’reusing this for the SC-1 Mic Preamp project. You probably won’t exactly get 48Volts, so using a small screwdriver, adjustleftmost trimmer R3 to measure 48 volts at the outputs. Turn the screwhead COUNTERCLOCKWISE to increase the voltage.

2. Next measure the voltage across (+) and GND pads. Adjust the middle trimmer R6 to get +18V at the outputs. Turn thescrewhead COUNTERCLOCKWISE to Increase the voltage

3. Next measure the voltage across (-) and GND pads. Adjust the rightmost trimmer R7 to get –18V at the outputs. Turn thescrewhead COUNTERCLOCKWISE to Increase the voltage Note... since this is a (-) supply, increasing the voltage will direct youtowards (0) zero volts. You'd want to decrease the voltage (i.e. turn CLOCKWISE) to adjust the voltage to -18Volts.

4. DONE! FINISH! Power off, then connect the (+), (-), GND and +48V pads to your SC-1 preamp or project.

Note: After connecting your preamp/load to the PSU… you may want to re-check the output voltages just to be sure. Re-adjust ifnecessary.

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PSU-1848 Modifications for +/-24Volts Output (i.e. a PSU-2448)

The PSU-1848 PSU can be modified for a higher +/-24V max output... useful if you're powering a Neve clone or some vintagegear that requires a higher voltage than +18V. And of course, +48V phantom power is still available.

The modifications are as follows:

R4 and R5 needs to be changed to 220 ohmsR6 and R7 trimmer needs to be changed to 5Kohm.

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Photos

Note the placement of the heatsinks. You need a 4-40x1/4 screw and a 4-10 hex nut to install the heatsinks to the TO-220regulators.

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PSU-1848/2448 Parts ListPart Value NotesIC1,IC2 LM317 RegulatorIC3 LM337 RegulatorD1,D2,D3,D4,D5,D6 1N4004 DiodesRECT1, REC72 W02G rectifierLED1,LED2 LITE-ON LED RED Clear red

R1,R8,R9 3K3R2 220RR3 5K TRIM Bourns top-adjust trimmerR4,R5 120R For +/-24V output, use 220R for R4,R5R6,R7 2K TRIM Bourns top-adjust trimmer For +/-24V output, use 5K TRIM for R6,R7

C1, C18 1000uf 80V Electrolytic Snap-in typeC3,C16,C17 10u 63V ElectrolyticC4,C14,C15 1u 63V ElectrolyticC6, C7 100uf 100V ElectrolyticC8,C9 1000uf 50V ElectrolyticC2,C5,C10,C11,C12,C13 0.1u 100V ceramic

H1,H2,H3 Heatsinks for TO-220PCB PSU-1848 PCB www.fivefish.net/diy

PSU-1848 PCB Component Layout Guide

Note: The long lead of the LED should be inserted at the bottom hole.