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AUDIO AMPLIFIERSAYED MUZZAMMIL ALI

SHAIKH AZHAR ASHRAFElectronics Department

MHSSCOE, Byculla, Mumbai-08

[email protected]

AbstractThe purpose of this report is to provide a brief

overview of the Audio Amplifier System. The Audio Amplifier

enjoys the honor of being the most commonly used Audio signal

generation technique. Over 85% of all low power audio signal

are produced fron Audio Amplifier.

Keywords Op-amp(UA741), Transistor ECN100 & ECP100,

Microphone CZ03, Loudspeaker of 2W.

I. INTRODUCTION

Audio Amplifier is an electronic amplifier that amplifies the

low-power audio signals (signals composed primarily of

frequencies between 20-20,000 Hz, the human range of

hearing) to a level suitable for driving loudspeakers and is the

final stage in a typical audio playback chain. Most of theaudio amplifiers require these low-level inputs to adhere to

line level. The audio amplifier was invented in 1909 by Lee

De Forest when he invented the triode vacuum tube.Audio

amplifier based on transistor became practical with the

availability of inexpensive transistor in the late 1960s.

II. DESIGN PROCEDURE

A. Block Diagram:

Fig 1: Block Diagram of Audio Amplifier

The figure 1 shows the block diagram of Audio Amplifier

System. The Audio Amplifier System consist of microphone,

pre-amplifier, tone and volume control or voltage amplifier,

power amplifier, loudspeaker.

MicrophoneThe microphone is a transducer which convert

sound to voltage.

Pre-amplifierThe pre-amplifier will amplifies the small

audio signal (voltage) from the microphone.Tone and Volume ControlThe tone and volume control

adjust the nature of the audio signal. The tone control adjust

the balance of high and low frequencies. The volume control

adjust the strength of the signal.

Power AmplifierThe power amplifier increases the

strength (power) of the audio signal.LoudspeakerThe loudspeaker is a transducer which

convert the audio signal or voltage signal to sound.

B. Circuit Diagram:

Fig 2: Circuit Diagram of 2W Audio Amplifier

As shown in Fig 2 the audio amplifier consist of three stages

i.e. microphone driving circuit, voltage amplifier, Class B

symmetrical amplifier. The input to the audio amplifier is

through the microphone driving circuit. The microphone

convert the audio signal into the voltage. The output of themicrophone driving circuit is applied to the input to the

voltage amplifier. The output of the microphone is in few

millivolts. The input to the voltage amplifier is in terms of few

millivolts. The output of the voltage amplifier is in terms of

few volts. The voltage amplifier will amplifies the voltage at

MK1

MICROPHONE

1

2

R1

1k

C1

4.7u

0

R2

1k

-

+

U1

UA741

3

2

6

7 1

4 5

R3

100k

0

V1

9v

0

V2

9v

0

LS1

SPEAKER0

V3

9v

Q1

2N3904

Q2

2N3906

V5

-15Vdc

V6

15Vdc

0

0
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the input. Depending upon the input voltage and the output

voltage, the gain of the voltage amplifier is decided. The

output of the voltage amplifier is applied to the Class B power

amplifier. The input voltage require for the Class B power

amplifier is few volts. The Class B push pull power amplifier

will amplifies for full cycle duration due to the two transistor

conduct for each cycle i.e. one transistor for positive half

cycle and one transistor for negative half cycle. Therefore,

both the transistor conduct for full cycle duration. The Class Bpower amplifier will avoid the cross-over distortion in the

Class B power amplifier. The power amplifier will amplify the

current by keeping the voltage at the same level and the output

of the power amplifier is applied to the loudspeaker. Theloudspeaker will convert the voltage into desired audio signal

and the output of the loudspeaker we get amplified audio

signal.

C. Component Calculation/ Analog Design:The design steps of the Audio Amplifier is as follows:

1. The microphone driving circuit consists of a resistorand a capacitor. The value of resistor R=1k and

capacitor C=4.7uf . The output of the microphone

driving circuit if few milivolts.

2. The voltage amplifier consist of the op-amp andthe resistor. The input to the voltage amplifier is

few volts i.e. 30mV and the output voltage requirefor the voltage amplifier is 2V. Therefore, the gain

of the amplifier is given by,

Av =

Depending upon the gain of the amplifier, the values

of resistor can be selected i.e. Ri = 1k and Rf =100k.

3. The Class B push pull power amplifier consist of thetwo transistor i.e. ECN100 and ECP100. The two

transistor conduct for full cycle duration i.e. the one

transistor for positive half cycle and the another

transistor for negative half cycle. The collector of

both the transistor are connected to the loudspeaker.

4. The loudspeaker used is of 2watts.

D. Component List:

MK1

MICROPHONE

1

2

R1

1k

C1

4.7u

0

V3

9v

R2

1k

-

+

U1

UA741

3

2

6

7 1

4 5

R3

100k

0

V1

9v

0

V2

9v

0

Q1

2N3904

Q2

2N3906

V5

-15Vdc

V6

15Vdc

0

0

LS1

SPEAKER0

Sr.

No.

Component Name Specification Quantity

Resistor

1. R1 1K 1

2. Ri 1K 1

3. Rf 100k 1

Capacitor

4. C1 4.7uf 1

OP-AMP

5. UA741 --- 1

Transistor

6. ECN100 and ECP100 --- 2

Microphone and Speaker

7. CZ03 and 2W speaker --- 2


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III. RESULTS

The 2W Audio Amplifier provides the combined effect of all

the three stages i.e. microphone driving circuit, voltage

amplifier and a power amplifier. The following result of the

audio amplifier is as follows:

1. The input to the microphone is audio signal of therange 20Hz-20KHz. The microphone driving circuitconvert this audio signal to a voltage. The output

voltage at the microphone driving circuit is 30mV.

2. The voltage amplifier will amplifies the 30mV ofthe voltage obtained from the microphone output to

the 2V which is required for the input of power

amplifier. The voltage amplifier consist of the OP-

AMP to amplify the voltage.3. The power amplifier will amplify the power level of

the amplifier by increasing the current level and by

keeping the voltage at the same level from the

output of voltage amplifier. the output of class B

power amplifier is applied to the loudspeaker.

4. The loudspeaker will produce the audio signal of2watts.

IV. APPLICATIONS

The Important application of Audio Amplifier are as follows:

1. It is used in public address system.2. It is used theatrical and cocert sound reinforcement

and in domestic sound system.

3. The sound card in a personal computer containseveral audio amplifier (depending on the number

of channel) as does every stereo and home-theatre

system.4. In Instrumental amplifier such as guitar amplifier.

V. CONCLUSION

The objective of this study was to develop a scheme to design

and study of Audio Amplifier. Also the response of individual

stage in the amplifier was also studied by taking output from

individual stage with respect to ground. The individual stage

stages of audio amplifier provides following features:1. The Microphone driving circuit provides the

voltage of few mV and it is applied to pre-

amplifier. The pre-amplifier will amplifies the

audio signal.

2. The Voltage amplifier will amplifies this signal ofmv to few ampunt of voltage and this voltage is the

input to the power amplifier.

3. The Power amplifier will amplifies the power levelof the signal, simply by increasing the current and

keeping the voltage same i.e. few voltage and at the

output of power amplifier we get amplified power

and this output is applied to the loudspeaker.

4. The loudspeaker will conert this signal to a sound.Thus the Audio Amplifier provides addition of all features

stated above.

VI. REFERENCES

1. Electronic Device and Circuit theory by Robert bolytested onpage no 347

2. www.alldatasheet.comVII. ENCLOSURES

1. Datasheet of UA7412. Datasheet of microphone CZ033. Datasheet of transistor ECN100 and ECP100


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