Design And Construction Of A 6W Power Amplifier

ABSTRACT

This work is titled the design and construction of power amplifier. A power 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. A power amplifier 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 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. The power amplifier in a radio transmitter operates over a relatively narrow band of frequencies with the load essentially constant impedance.

It can be used to amplify the sound of audio sound system like 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 BACKGROUND OF THE PROJECT

1.2 AIM OF THE PROJECT

1.3 OBJECTIVE OF THE PROJECT

1.4 PURPOSE OF THE PROJECT

1.5 APPLICATION OF THE PROJECT

1.6 SIGNIFICANCE OF THE PROJECT

1.7 LIMITATION OF THE PROJECT

1.8 TERMS AND DEFINITIONS

1.9 PROJECT ORGANISATION

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 HISTORICAL 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

3.3 CIRCUIT OPERATION

3.4 CIRCUIT DESCRIPTION

3.5 POWER SUPPLY CIRCUIT

3.6 PARTS LIST

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 CONCLUSION

5.2 RECOMMENDATION

5.2 REFERENCES

CHAPTER ONE

1.0 INTRODUCTION

An audio 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.

An audio 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, an audio 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.

An audio 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 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.

1.1                                          BACKGROUND OF THE PROJECT

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 of the individual using the microphone from shouting. The power output of the speaker depends on the power rating of the loudspeaker and that of the amplifier.

Moreover, an amplifier may be defined as a system or an electronic circuit which accepts signals at its input and gives out signals at its output greater than the signal at its input in amplitude or power or current. The output signal is similar to the input signal in shape, form and frequency

1.2                                                      AIM OF THE PROJECT

The main aim of this work is to design and construct an audio amplifier that will deliver appreciable power of 6W to a load (speaker).

1.3                                          OBJECTIVE OF THE PROJECT

At end of this work student involved in this project shall be able:

1. To understand the operation of an audio amplifier
2. To read and analyze the circuit diagram of an amplifier

• Understand the wiring and configuration of transistors

1. To understand the impact of heat sink on transistors

1.4                                          PURPOSE OF THE PROJECT

The purpose of this work is to amplify low-power electronic audio signals such as the signal from radio receiver or electric guitar pickup to a level that is high enough for driving loudspeakers or headphones. Amplifier takes weak signal and make it strong to drive a speaker. An audio 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                                          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.

1.6                                          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.

1.7                              PROBLEM / LIMITATION OF THE PROJECT

1. 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.
2. Limited output voltage, current, and power levels. This amplifier is limited to 10w as the output power..

1.8                                                      DEFINITION OF TERMS

Acoustics – the science or study of sound.

Alternating (AC) Current – currents that have a harmonic time dependence.

Ampere (A) – the unit of measurement for electrical current in coulombs per second.

Amplifier – an electrical circuit designed to increase the current or voltage of an applied signal.

Audio frequency – the acoustic spectrum of human hearing, generally regarded to be between 20 Hz and 20 kHz.

Capacitor – a charge storage device made up of two metallic plates separated by a dielectric, with equal but opposite charges. The AC impedance of a Capacitor is (1 / jWL) and acts as an open circuit in DC applications.

Circuit – a complete path that allows electrical current from one terminal of a voltage source to the other terminal.

Class A – transistor amp conducts for the entire cycle of input signal, conduction angle 360 deg. Runs hot, as the transistors in the power amp are on all the time, but has high sound quality.

Class B – positive and negative halves of the signal dealt with by different parts of the circuit, the output devices switching continually. Runs cooler, but the sound is not as pure.

Class AB – biasing the transistor amp at a non-zero DC current much smaller than the peek current of the signal source. Second transistor conducts during negative half cycle of waveform and the currents from the 2 transistors are combined at the load. A compromise between sound quality of Class A and efficiency of Class B. Most amp designs employ this method.

Current (I) – the flow of electrical charge measured in amperes.

Decibel (dB) – (1) a logarithmic scale used to denote a change in the relative strength of an electric signal or acoustic wave. It is a standard unit for expressing the ratio between power and power level. Using the logarithmic relationship for power PdB = 10*log[Pout/Pin] , a doubling of electrical power only yields an increase of +3 dB. Increasing the power tenfold will yield an increase of +10 dB and is a doubling of perceived loudness. The decibel is not an absolute measurement, but indicates the relationship or ratio between two signal levels. (2) SPL (sound pressure level) can be measured in dB. 0 dB represents the threashold of normal human hearing, 130 dB represents the threashold for pain, 140 dB causes irreparible hearing damage, and 150 dB can cause instant deafness, anything greater than about 192 dB can kill you.

Direct Current (DC) – current in only one direction.

Driver – a loudspeaker unit, consisting of the electromagnetic components of a speaker, typically a magnet and voice coil.

Enclosure – a box that contains the driver(s).

Equalizer – electronic device that acts as active filters used to boost or attenuate certain frequencies. Farad – the basic unit of capacitance. A capacitor has a value of one farad when it can store one coulomb of charge with one volt across it.

Filter – any electrical circuit or mechanical device that removes or attenuates energy at certain frequencies. See Crossover Network.

Frequency – the number of waves (or cycles) arriving at or passing a point in one second, expressed in hertz (Hz).

Frequency Response – the frequency range to which a system, or any part of it, can respond.

Full-range – a speaker designed to reproduce all or most of the sound spectrum within human hearing (20Hz – 20KHz).

Ground – refers to a point of zero voltage or potential.

Harmonic – the multiple frequencies of a given sound, created by the interaction of signal waveforms.

Hertz (Hz) – a measurement of the frequency of sound vibration. One hertz is equal to one cycle per second. The hertz is named for H.R. Hertz, a German physicist.

High-pass Filter – an electric circuit that passes high frequencies but blocks low ones by acting as a large impedance to those frequencies. See Band-pass and Low-pass filters.

Hum – audio noise that has a steady low frequency pitch.

Imaging – it is the speakers ability to localize different instruments playing simultaneously. See Soundstage.

Impedance – dependent on frequency, it is the AC equivalent of resistance in a DC circuit.

Inductance (L) – the capability of a coil to store energy in a magnetic field surrounding it. It produces an impedance to an AC current (jwL) and acts as a short circuit to DC. Inductors are commonly used in audio as low pass crossovers. See Le.

Input – connection from signal source.

Maximum power rating – a value which means almost nothing, but is used nonetheless by manufacturers to entice the unsuspecting into purchasing their product based solely on the big number. Technically, it is the maximum wattage that an audio component can deliver/handle as a brief burst during a musical peak. Most reputable manufacturers will provide both an RMS and Max power rating. Typically, the given value for the maximum power rating is twice to three times that of RMS.

Microfarads (mF) – a measurement of capacitance (XC*10^-6).

MOFSET – Metal Oxide Semiconductor Field Effect Transistors. Used in most modern, quality car audio amplifiers in the power supply (and sometimes in the output stage). MOSFET’s run cooler than normal bipolar transistors, and have a faster switching speeds and higher slew rates.

Ohm – a unit of electrical resistance or impedance.

Ohm’s Law – a basic law of electric circuits. It states that: the current [I] in amperes in a circuit is equal to the voltage [V] in volts divided by the resistance [R] in ohms; thus, I = V/R.

Oversampling – used in DAC systems. Increases signal frequency, making it easier for conversion circuitry and ancillary systems to filter out unwanted signals.

Out of Phase – when your speakers are mounted in reverse polarity, i.e., one speaker is wired +/+ and -/- from the amp and the other is wired +/- and -/+. Bass response will be very thin due to cancellation.

Output – the sound level produced by a loudspeaker.

Peak – the maximum amplitude of a voltage or current.

Phase – Refers to the timing relationship of two or more signals or soundwaves. It’s especially important to be sure that your stereo speakers are playing “in phase.” This means that the drivers (cones and domes) of your right and left speakers are moving in and out at the same time. If your speakers are “out of phase” you’ll hear significantly less bass, and instead of producing a strong center image, the sound tends to stay localized at the speakers.

Phase Coherence – the relationship and timing of sounds that come from different drivers (subs, mids, tweets) mounted in different locations in the vehicle.

Phase Distortion – a type of audible distortion caused by time delay between various parts of the signal; can be caused by equalizers.

Polarity – the orientation of magnetic or electric fields. The polarity of the incoming audio signal determines the direction of movement of the speaker cone. Must be observed when wiring speakers, so that they are “in phase”. See Out of Phase.

Power (P) – the time rate at which work is done or the rate at which energy is used. Basic equations for Electrical Power are: P = V^2/R or P = I^2*R.

Resistance (Re) – in electrical or electronic circuits, a characteristic of a material that opposes the flow of electrons. The higher the gauge of wire, the less cross sectional area contributing to DC series resistance (DCR).

RMS – an acronym for “root mean square.” Used in audio to help rate the continuous power output of an amplifier or input capability of speakers. This is the preferred method for comparing anything in audio applications.

Sensitivity – The sound pressure level directly in front of the speaker (on axis) at a given distance (usually 1 meter) produced by a given amount of power (usually 1 watt).

Signal-to-noise (S/N) – the ratio, expressed in dB, between the signal and noise.

Volt (E) – a unit of measurement used to measure how much “pressure” is used to force electricity through a circuit.

Watt – a unit of electrical power. A watt of electrical power is the use of one joule of energy per second. Watts of electrical power equals volts times amperes.

1.9                                          PROJECT WORK ORGANISATION

The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:

Chapter one of this work is on the introduction to an audio amplifier. In this chapter, the background, significance, objective limitation and problem of an audio amplifier were discussed.

Chapter two is on literature review of an audio amplifier. In this chapter, all the literature pertaining to this work was reviewed.

Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.

Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references. Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.

Chapter five is on conclusion, recommendation and references.