This thesis gives the account for the design and construction of a 45W Audio Power Amplifier with the objective of producing a reliable and cheaper amplifier that can be used in a household or stage.

The Audio Power Amplifier was constructed with electrical/electronics components such as resistors, capacitors, transformer, transistors and so on. Many tools/instruments like soldering iron, multimeter and so on were used.

The 45W Audio Power Amplifier when compared with other types of Audio Power Amplifier of the same rating in the market is cheaper as the components and materials used were locally sourced and selected to suit the desired purpose and environment.

LIST OF TABLES, GRAPHS AND FIGURES

Figure 1.1 circuit diagram of a 25W Audio Power Amplifier

Figure 2.1 Resistor colour band table

Figure 2.2aColour code marking on a resistor

Figure 2.2b Circuit symbol of resisitor

Figure 2.3 Circuit symbols of capacitor

Figure 2.4 Diode circuit symbol

Figure 2.5aFormation of potential barrier

Figure 2.5bForward biasing a P-N junction diode

Figure 2.5c Reverse biasing a P-N junction diode

Figure 2.6aStructure and symbol of p-n-p and n-p-n transistor

Figure 2.6bBiasing of a transistor

Figure 2.7 Structure of an IC

Figure 2.8 JRC 4558IC circuit diagram

Figure 3.1aThe power supply circuit diagram

Figure 3.1bBlock diagram of a power supply unit

Figure 3.2aThe Pre-amplifier circuit diagram

Figure 3.2bThe OP-amp audio mixer

Figure 3.3 The tone control circuit

Figure 3.4aA complementary symmetry class B amplifier

Figure 3.4bThe output stage of the public address system

Figure 4.1 The circuit layout diagram

Figure 4.2 The body construction diagram (case)

Figure 4.6 Costing table.

Title page

Dedication

Acknowledgement

Approval page

Abstract

List of tables, graph and figures

CHAPTER ONE

1.1 Introduction

CHAPTER TWO: DESCRIPTION OF CIRCUIT ELEMENT

2.1 Resistors

2.2 Capacitors

2.3 Diodes

2.4 Bipolar Junction Transistor (BJT)

2.5 Integrated Circuits (ICs)

CHAPTER THREE: PRINCIPLE OF OPERATION

3.1 Power supply

3.2 Pre-amplifier

3.3 Tone control

3.4 Power amplifier

CHAPTER FOUR: CONSTRUCTION AND TESTING

4.1 Breadboard/Prototyping

4.2 Circuit layout

4.3 Construction

4.4 Testing and Result

4.5 Packaging

4.6 Costing

CHAPTER FIVE: CONCLUSION/RECOMMENDATION

References

CHAPTER ONE

1.1 INTRODUCTION

Many centuries back people found it difficult to be heard over a few metres away from them while addressing their audience. This motivated the need for man to pursue new technologies which will increase his reliability and efficiency. Man in search of the audio boosting instrument developed an aspect of communication called “Public Address System (PAS)”, which helps an individual to address or communicate to a large group of people. Through this system for instance, a clergyman can address his congregation, an entertainer can communicate to his audience, a politician can address his supporters and so on.

The Public Address System (PAS) comprises of a microphone which converts sound energy to electrical energy, an amplifier which increases the strength of the electrical signals and a loudspeaker which reconverts the electrical energy of the signals to sound energy.

In the PAS, the sound energy at the loudspeaker has greater power than that at the microphone hence, the sound is more louder. This reduces the stress