Description
This work is titled the design and construction of 60W transistor based audio amplifier. Transistor based audio amplifier is a device for increasing the audio power of a signal by use of an external energy source. It is design to meet up with the amplification demand in homes, offices, industries and especially in music industries. Transistor based audio amplifier r amplifies 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, While the input signal to an audio amplifier may measure only a few hundred microwatts, its output may be tens, hundreds, or thousands of watts.
This device is designed to deliver appreciable 60w power to the load. Audio Power amplifiers may be called upon to supply power ranging from a few watts in an audio amplifier to many hundreds or thousands of watts to a load (speaker). In audio amplifiers the load is usually the dynamic impedance presented to the amplifier by a loudspeaker, and the function is to maximize the power delivered to the load over a wide range of frequencies.
60w amplifier when constructed can produce up to 80 watts (w) of audio signal. It can be sued to amplify the sound of audio sound system like mini radio cassette player, compact disc player, turn table record player, car radio cassette player or any other sound system that requires increased audio.
This amplifier when produced in large or commercial quality, according to purpose will create job opportunity, provide indigenous electronics technology industry, and it will contribute to economic growth of the nation.
TABLE OF CONTENTS
Title Page
Approval Page
Dedication
Acknowledgement
Abstract
Table of Content
CHAPTER ONE
1.0 Introduction
1.1 Objective of the project
1.3 Application of the project
CHAPTER TWO
2.0 Literature review
2.1 Historitical background of an amplifier
2.2 Review of classification of power amplifiers
2.3 Classification according to mode of operation
2.4 Review of transistor biasing
CHAPTER THREE
3.0 Construction
3.1 Block diagram of an audio power amplifier
3.2 Circuit diagram of a 60w amplifier
3.3 Circuit operation
3.4 Circuit description
3.5 Power supply circuit
3.6 Parts list of 60 watt amplifier circuit
3.7 Description of components used
CHAPTER FOUR
RESULT ANALYSIS
4.0 Construction Procedure and Testing
4.1 Casing and Packaging
4.2 Assembling of Sections
4.3 Testing of System Operation
4.4 Cost Analysis
CHAPTER FIVE
5.1 summary
5.2 References
CHAPTER ONE
1.0 INTRODUCTION
An audio power amplifier is an electronic amplifier that amplifies 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. It is the final electronic stage in a typical audio playback chain.
Power Amplifier (also known as a large signal amplifier), is to deliver power to the load, and as we know from above, is the product of the voltage and current applied to the load with the output signal power being greater than the input signal power. In other words, a power amplifier amplifies the power of the input signal which is why these types of amplifier circuits are used in audio amplifier output stages to drive loudspeakers.
The power amplifier works on the basic principle of converting the DC power drawn from the power supply into an AC voltage signal delivered to the load. Although the amplification is high the efficiency of the conversion from the DC power supply input to the AC voltage signal output is usually poor.
The preceding stages in such a chain are low power audio amplifiers which perform tasks like pre-amplification (this is particularly associated with record turntable signals), equalization, tone controls, mixing/effects, or audio sources like record players, CD players, and cassette players. Most audio power amplifiers require these low-level inputs to adhere to line levels.
While the input signal to an audio power amplifier may measure only a few hundred microwatts, its output may be tens or hundreds of watts for a home system or thousands or tens of thousands of watts for a concert sound reinforcement system.
Not all amplifiers are the same and are therefore classified according to their circuit configurations and methods of operation. In “Electronics”, small signal amplifiers are commonly used devices as they have the ability to amplify a relatively small input signal, for example from a Sensor such as a photo-device, into a much larger output signal to drive a relay, lamp or loudspeaker for example.
There are many forms of electronic circuits classed as amplifiers, from Operational Amplifiers and Small Signal Amplifiers up to Large Signal and Power Amplifiers. The classification of an amplifier depends upon the size of the signal, large or small, its physical configuration and how it processes the input signal, which is the relationship between input signal and current flowing in the load.
1.2 OBJECTIVE OF THE PROJECT
The main objective of this work is to design and construct an audio power amplifier that will deliver appreciable 60w power to the load. transistor based audio amplifier may be called upon to supply power ranging from a few watts in an audio amplifier to 60 watts to a load (speaker).
1.3 APPLICATION OF THE PROJECT
Important applications include public address systems, theatrical and concert sound reinforcement systems, and domestic systems such as a stereo or home-theatre system. Instrument amplifiers including guitar amplifiers and electric keyboard amplifiers also use audio power amplifiers. In some cases, the power amplifier for an instrument is integrated into a single amplifier “head” which contains a preamplifier, tone controls, and electronic effects. In other cases, musicians may create a setup with separate rack mount preamplifiers, equalizers, and a power amplifier in a separate chassis.
1.4 PURPOSE OF THE PROJECT
Amplifier’s main purpose is to take the weak signal and make it strong to drive a speaker. The power amplifiers usually get necessary amplification energy of input signals from the AC supply. Ideally without distortion an amplifier can deliver signal at the output without distortion.
1.5 SIGNIFICANCE OF THE PROJECT
Today there are many categories of amplifiers used for multifarious purposes. In simple terms an amplifier picks up a weak signal and converts it into a strong one. It is widely used in several devices to boost electrical signals. Radios, televisions and telephones are a few examples to point out in this regard. There are innumerable other applications of amplifiers and it is not easy to enumerate all of them. Some of the common types of amplifiers are used in electronic gadgets and audio systems. These are also used in musical instruments and guitars.
1.6 LIMITATION OF THE PROJECT
- Noise. This device tends to add some random noise to the signals passing through them, hence degrading the SNR (signal to noise ratio). This, in turn, limits the accuracy of any measurement.
- Limited output voltage, current, and power levels. This amplifier can’t output signals above 60w.
CHAPTER FIVE
5.1 SUMMARY
Amplifiers are used extensively in electronic circuits to make an electronic signal bigger without affecting it in any other way. Generally we think of Amplifiers as audio amplifiers in the radios, CD players and stereo’s we use around the home. In this amplifier tutorial section we looked at the amplifier which is based on a single bipolar transistor as shown below, but there are several different kinds of transistor amplifier circuits that we could use.
Small Signal Amplifiers are also known as Voltage Amplifiers.
- Voltage Amplifiers have 3 main properties, Input Resistance, Output Resistance and Gain.
- The Gain of a small signal amplifier is the amount by which the amplifier “Amplifies” the input signal.
- Gain is a ratio of input divided by output, therefore it has no units but is given the symbol (A) with the most common types of transistor gain being, Voltage Gain (Av), Current Gain (Ai) and Power Gain (Ap)
- The power Gain of the amplifier can also be expressed in Decibels or simply dB.
- In order to amplify all of the input signal distortion free in a Class A type amplifier, DC Base Biasing is required.
- DC Bias sets the Q-point of the amplifier half way along the load line.
- This DC Base biasing means that the amplifier consumes power even if there is no input signal present.
- The transistor amplifier is non-linear and an incorrect bias setting will produce large amounts of distortion to the output waveform.
- Too large an input signal will produce large amounts of distortion due to clipping, which is also a form of amplitude distortion.
- Incorrect positioning of the Q-point on the load line will produce either Saturation Clipping or Cut-off Clipping.
- The Common Emitter Amplifier configuration is the most common form of all the general purpose voltage amplifier circuit using a Bipolar Junction Transistor.
- The Common Source Amplifier configuration is the most common form
of all the general purpose voltage amplifier circuit using a Junction Field Effect Transistor.
- Large Signal Amplifiers are also known as Power Amplifiers.
- Power Amplifiers can be sub-divided into different Classes, for example:
- Class A Amplifiers– where the output device conducts for all of the input cycle.
- Class B Amplifiers– where the output device conducts for only 50% of the input cycle.
- Class AB Amplifiers– where the output device conducts for more than 50% but less than 100% of the input cycle.
- An ideal Power Amplifier would deliver 100% of the available DC power to the load.
- Class A amplifiers are the most common form of power amplifier but only have an efficiency rating of less than 40%.
- Class B amplifiers are more efficient than Class A amplifiers at around 70% but produce high amounts of distortion.
- Class B amplifiers consume very little power when there is no input signal present.
- By using the “Push-pull” output stage configuration, distortion can be greatly reduced.
- However, simple push-pull Class B Power amplifiers can produce high levels of Crossover Distortion due to their cut-off point biasing.
- Pre-biasing resistors or diodes will help eliminate this crossover distortion.
- Class B Power Amplifiers can be made using Transformers or Complementary Transistors in its output stage.
