ABSTRACT
It has become inevitable that there would be communication and due to the inherent limitation of the human voice, the public address system came to being. A public address or “P.A SYSTEM” is an electronic amplification system with a mixer ,amplifier and loudspeakers, used to reinforce a given sound , e.g a person making a speech, pre-recorded music ,or message and distributing the sound throughout a venue . The voice signal is passed through a microphone , which converts the sound energy to electrical energy, the energy electrical signal being transmitted is been received and amplified by the amplifier circuit. The amplifier’s output is fed into the loudspeaker which converts the electrical energy back to the original form but amplified sound energy. This project is made up of the power supply unit, the pre-amplifier and power amplifier units, and the tone control unit. This system is capable of delivering 20W of electrical power into a 8 ohm load(loudspeaker).
TABLE OF CONTENTS
Certification Page------------------------------------------------------------------------ i
Dedication ---------------------------------------------------------------------------------ii
Acknowledgement------------------------------------------------------------------------iii
Abstract-------------------------------------------------------------------------------------iv
Table of contents---------------------------------------------------------------------------v
List of Table--------------------------------------------------------------------------------vii
List of figures------------------------------------------------------------------------------viii
1.1 BACKGROUND OF THE STUDY
1.2 Aims and Objectives……………………………………………..5
1.3 Justification ……………………………………………..6
1.4 Scope of project …………………………………………….7
1.5 System block diagram……………………………………………7
1.6 Project Work Organization ………………………………………8
2.1 Ancient medium of information transmission …………………….9
2.2.1 Problems associated with earlier systems…………………..……10
2.2.2 Working principles of the modern systems………………………10
2.3 Public Address System…………………………………………..11
2.3.1 The transmitter system…………………………………………..12
2.3.2 The Receiver system…………………………………………….13
2.3.3 The Antenna……………………………………………………..14
2.3.3.1 Functions of Antenna……………………………………………15
2.3.4 The tone control and mixer stage………………………………..15
2.3.5 The audio amplifier……………………………………………..16
2.3.6 The loudspeaker…………………………………………………17
2.4 Modulation………………………………………………………17
2.4.1 Frequency modulation…………………………………………..18
CHAPTER 3: SYSTEM DESCRIPTION AND IMPLEMENTATION….19
3.1 Transistor power amplifier……………………………………….19
3.2 MOSFET power amplifier………………………………………..19
3.3 Bipolar junction transistor………………………………………...21
3.4 Operational Amplifier……………………………………………..23
3.4.1 Class A amplifier………………………………………………….24
3.5 Implementation Method…………………………………………..24
4.1 Power Supply unit design………………………………………….26
4.2 Transmitter design ………………………………………………..27
4.3 Amplifier circuit design…………………………………………....29
4.4 Receiver principles………………………………………………...31
4.5 Demodulation……………………………………………………...32
4.6 Transmitter circuitry…………………………………………….…33
4.7 The input stage…………………………………………………….34
4.8 Mixing stage………………………………………………………34
4.9 Audio power amplifier…………………………………………….36
5.1 The power supply …………………………………………………37
5.2 The output power amplifier………………………………………..37
5.3 Dissipation of excessive heat………………………………………38
5.4 Entire circuit testing………………………………………………..38
5.5 Performance Evaluation…………………………………………...38
5.6 Packaging……………………………………………………….....40
6.1 Bill of Engineering measurement and Evaluation (BEME)……….41
6.2 Problems Encountered and Solution……………………………….42
6.3 Audio feedback and prevention……………………………………43
6.5 Conclusion…………………………………………………………44
6.6 Recommendation / Reference ……………………………………44
