DESIGN AND CONSTRUCTION OF AN AUDIO AMPLIFIER

ABSTRACT

This project involved design and construction of an audio amplifier that could drive a quite number of speakers. This was achieved by coupling different stages of amplification together with a coupling element where the output of one stage serves as input to the next stage. The stages are, Preamplifier stage, Mixer Stage, Volume Control Stage, power output stage. This construction work resulted into an audio amplifier which can be used in Radio Receiver, Cassette Players, Video Players, Public Address System. An audio amplifier is a device for increasing the power of a signal i.e. makes sound louder and signal level greater. It does this by taking power from the power supply and controlling the output to match the input signal shape but with large amplitude. A signal can be large in terms of its voltage level, current level or both, but in electronic system, a speaker requires several watts for good volume.

LIST OF FIGURES

Fig 1.0: Showing a transformer

Fig 1.1: A Vero Board

Fig 1.2a: NPN Negative Collector, Positive base and Negative Emitter

Fig 1.2b: PNP Positive Collector, Negative base and Positive Emitter

Fig 1.3: Symbol of the two types of transistor configuration

Fig 1.4: Symbol of a resistor

Fig 1.5: Symbol of a variable resistor

Fig 1.6a: Symbol of a capacity

Fig 1.6b: Symbol of a variable capacitor

Fig 1.7a: Rectifier Diode

Fig. 1.7b: Zener Diode

Fig. 1.7c: Light Emitting Diode

Fig. 1.7d: Photo Diode

Fig 1.7e: Schotty Diode

Fig 1.8: Symbol of Operational amplifier

Fig 1.9 Figure showing the appearance of an IC

Fig 1.10 The diagram above illustrates the process of testing resistor

Fig 1.11 The diagram above illustrates the process of testing transistors

Fig 1.12: The diagram above illustrates the process of testing transistors

Fig 1.13: Transformer

Fig 3.10: Diagram showing Design Technique

Fig 3.11 Data Sheet

Fig 3.12 Class B Push Pull Transistor Amplifier with wave forms

Fig 3.13 PreAmplifier Circuit

Fig 3.14 Mixer Circuit

Fig 3.15: Tone Control Circuit

Fig 3.16 Volume Control Circuit

Fig 3.17 Power Output Amplifier Circuit

Fig 3.18: Block Diagram Illustrating Power Supply Circuit

Fig. 3.19: Power Supply Circuit

Fig 4.10: Diagram showing the wave forms of the input and output signal from each stages

Fig 4.11: Front View of Structure of the Case

Fig 4.12 Back View of Structure of the Case

LIST OF TABLES

Table 2.0: Table showing Resistor Colour Codes with their corresponding Values

Table 4.0: Table Showing the faults, causes and actions.

TABLE OF CONTENTS

Title Page................................................................................................... i

Certification. iii

Dedication. iv

Acknowledgementv

Abstractvii

List of Figuresviii

List of Tablesx

Table of Contentsxi

Chapter One1

Introduction. 1

Aim and Objectives2

Scope of Study And Limitation. 2

Justification. 3

Chapter Two. 4

Literature Review. 4

Component Description. 5

The Transformer5

Vero Board. 6

Transistors7

Resistors8

Variable Resistor11

Capacitor11

Diodes12

Integrated Circuit Ic14

Testing of Components16

Testing Resistors16

Testing Transistors17

Testing Diodes17

Testing Capacitor18

Testing the Transformer18

Testing Integrated Circuit Ic19

Chapter Three20

Design Technique20

List of Components and Materials21

Components Used in PreAmplifier Stage21

Components Used Mixer Stage21

Components Used in Tone Control Stage21

Components Used in Volume Control Stage22

Stage Components Used in Power Output22

Components at the Power Supply Circuit22

Materials Used. 24

Integrated Circuit24

Operational Amplifier25

JRC 4558. 26

Class B Push Pull Transistor Amplifier27

Construction. 29

Amplifier Stages29

Microphone Stage30

PreAmplifier Stage30

Mixed Stage32

Tone Control Stage33

Volume Control Stage35

Power Output Stage36

Power Supply Stage39

Chapter Four41

Load And Impedance Matching. 41

Circuit Analysis41

Noise44

Trouble Shooting Amplifier Circuit46

Transistor Troubles47

In Circuit Test47

Measuring Collector Current48

Checking The Emitter Circuit48

Fault Analysis48

Structure Of The Case52

Chapter Five54

Principle Of Operation. 54

Testing The Amplifier54

Precaution And Maintenance54

The Safety Measures Towards Burning. 55

Application. 56

Chapter Six. 57

Conclusion. 57

Recommendation. 57

References59