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 addressP.A SYSTEMor ”“  is   an   electronic   amplific ,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’soutputis 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

                                   

CHAPTER 1:

INTRODUCTION

1.1

BACKGROUND OF THE STUDY

1.2

Aims and Objectives

1.3

Justification

 

1.4

Scope of project

1.5

System   block   diagram

1.6

Project Work Organization

CHAPTER 2:

LITERATURE REVIEW

2.1

Ancient medium of information transmission

2.2

Modern day medium Approach

2.2.1

Problems associated with earlier systems

2.2.2

Working principles of the modern systems

2.3

Public Address System

2.3.1

The transmitter system

2.3.2

The Receiver system

2.3.3

The Antenna

       

 2.3.3.1                               Functions of Antenna

 2.3.4

The tone control and mixer stage

2.3.5

The audio amplifier

2.3.6

The loudspeaker

2.4

Modulation

2.4.1

Frequency modulation

 CHAPTER 3:

SYSTEM DESCRIPTION AND IMPLEMENTATION

3.1

Transistor power amplifier

3.2

MOSFET power amplifier

3.3

Bipolar junction transistor

3.4

Operational Amplifier

3.4.1

Class A amplifier

3.5

Implementation Method

CHAPTER 4:   CIRCUIT DESIGN AND ANALYSIS

4.1

Power Supply unit design

4.2

Transmitter design 

4.3

Amplifier circuit design

4.4

Receiver principles

4.5

Demodulation

4.6

Transmitter circuitry

4.7

The input stage

4.8

Mixing stage

4.9

Audio power amplifier

CHAPTER 5:

CONSTRUCTION AND TESTING

5.1

The power supply

5.2

The output power amplifier

5.3

Dissipation of excessive heat

5.4

Entire circuit testing

5.5

Performance Evaluation

5.6

Packaging

CHAPTER 6:CONCLUSION AND RECOMMENDATION

6.1

Bill of Engineering measurement and Evaluation (BEME)

6.2

Problems Encountered and Solution

6.3

Audio feedback and prevention

6.5

Conclusion

6.6

Recommendation / Reference

         

  CHAPTER ONE

INTRODUCTION

1.1                              BACKGROUND OF THE STUDY

 A public address system allows you to broadcast information to a large group of people, whether you are giving a speech or playing live or recorded music.

Public address systems typically consist of input sources, preamplifiers, control and monitoring equipment, and loudspeakers. Input sources refer to the microphones that provides a sound input for the system. These input sources are fed into the preamplifiers. The pre amplified signals are then passed into the audio power amplifiers.

These amplifiers will amplify the audio signals to an adequate speaker line level. In view of the above, one can now say that the public address system is an electronic amplification system used for communication in public areas.

 Microphone is a device that converts sound waves into electrical waves. Some

times colloquially called a micro mike is an acoustic-to-electric transducer or sensor that converts sound into an electrical signal. Microphones are used in many applications such as telephones, hearing aids, live and recorded audio engineering, in radio and television broadcasting and in computers for recording voice, and for non-acoustic purposes such as ultrasonic checking. The sensitive transducer element of a microphone is called its element. Since a wireless microphone is used in this project; a wireless microphone is one in which communication is not limited by a cable.

A transmitter  is  extremely  important  equipment  and  is  housed  in  the

broadcasting station. Its purpose is to produce radio waves for transmission into space. The important components of a transmitter are microphone, audio amplifiers, oscillator and modulator.

It usually sends its signal using a small FM radio transmitter to a nearby receiver connected to the sound system, but it can also use infrared light if the transmitter and receiver are within sign of each other. The transmitter are responsible for taking in the signal from the microphone, modulating it, and transmitting it to the receiver using radio waves.

The first transistor (Q1) is the pre-amplifier for the microphone, and you can omit this circuit ifsmit youthesound don’tpickedupby thewantmic,for exampleto tran you can connect your mp3 player directly to C1. The core of this FM transmitter

circuit is Q2, a modified Culprits oscillator that the frequency is determined by L1,

C4, C6, and the etransistor’s-emittercapacitance.Theantennainternaluse1/16 wave length to compromise between the efficiency and the size. If you want the microphone to be less sensitive, we can replace the R1 by a higher resistor, such as 10k or 22k, and this might overcome the feedback problem if you use this wireless microphone FM transmitter for a public address system

 The receiver captures the radio waves sent out by the transmitter, demodulates

the signal, amplifies it to an appropriate level, and sends it out to the audio mixer. A receiver is an electronic circuit that receives its input from an antenna, uses electronic filters to separate a wanted radio signal from all other signals picked up by this antenna, amplifies it to a level suitable for further processing, and finally converts through demodulation and decoding the signal into a form usable for the consumer, such as sound, and digital data, etc.

Amplifier or simply amp is any device that changes, usually increases, the

amplitude of a signal. The “signal” is device for increasing the power of a signal. It does this by taking energy from a power supply and controlling the output to match the input signal shape but with larger amplitude. Routing the low-frequency parts of the signal to an amplifier can substantially improve the clarity of the overall sound reproduction.

In this project, the audio amplifier used is capable of delivering 20watts continuously. The term “power amplifier” is a relat amount of power delivered to the load and/or sourced by the supply circuit.

In general a power amplifier is designated as the last amplifier in a transmission chain (the output stage) and is the amplifier stage that typically requires most attention to power efficiency. Power amplifiers have also become lighter, smaller, more powerful and more efficient due to increasing use of Class A amplifiers, which offer significant weight and space savings as well as increased efficiency.

Power ampli