AKINWANDE MOSHOOD ABIOLA.docx

8/14/2019 AKINWANDE MOSHOOD ABIOLA.docx

1/19

1

CHAPTER ONE

1.0 INTRODUCTION

The need for an amplifier arose when signals of higher amplitudes required at

the electronic system. From the definition of an amplifier as a device that receives a

signal from present stage transducer or other input source and provide a large version

of the signal to some output device or another amplifier stage. These must be a

prescribed relationship between the input and output signals, be it voltage or current.

Normally the relationship is required to be linear, So that the output signal is widely

used in such equipment as radio, high fidelity (HiFi) equipment, television and

computers.The amplifier may be required to deliver appreciable output power, from instant to

operate loudspeaker system or to feed a transmitter antenna, power amplifier is

design to deliver a specific output power into a related load when a suitable signal

(like 20Hz to 20kHz) of this is applied to its input.

Modern technology favour the use of transistor and integrated circuit (I C) in

the construction of audio amplifier and this is fully adopted in this project work.

Also, resistance and capacitor coupling is used between two amplifier stages because

of its simplicity, good frequency response and low cost. Also, cascading is easily

down in this project because transistor in the amplifier stage is operated in the

common-emitter configuration. The completed voltage amplifier consists of the pre-

amplifier, the mixer and the tone controls which also serve as the equalizer.

The ratio of the output current or voltage power to the corresponding quantity

all expressed in the same unit is the gain of the amplifier.

Furthermore, amplifiers are necessary in most application because the desired

(actual) signal usually too weak to be directly useful. Example is the audio output

from a microphone (mw) where the loudspeaker needs a few volt of audio signal.

However, with an amplifier a whisper could fill a large room with sound. However,

voltage amplifier produce voltage amplification primarily to increase the voltage of

input signal, while large signal or power amplifier primarily provides sufficiency

power to an output load which could be a speaker or other power device of a few

watts (w) to tens of watt.


2/19

2

1.1. STATEMENT OF THE PROBLEM

It is important or necessary for an integrated circuit power amplifier to take

an input signal and make it stronger or increase its amplitude at the output.

1.2. SIGNIFICANCE OF THE STUDY

The importance of this project is to make it easier for people or audience to hear

someone from distance or a specify place that the amplifier can cover so as to make

an undisturbed output, to composed primarily of frequencies between 20-20000hz

the human range of hearing to a suitable for driving loudspeakers.

1.3 OBJECTIVE OF THE PROJECT

The aim and objective of this project is to construct a 20 watts amplifier that can

amplify the poor of message signal to be transmitted.

1.4 SCOPE OF THE RESEARCH PROJECT

The scope of this project is to design an amplifier which it will not go beyond 20watt

amplifier and make it perfect for almost any home audio where space is limited.

1.5 DEFINITION OF TERMS

(i) Integrated circuit: It permits the construction of completed multistage

amplifier and other linear device on a single silicon clip.

(ii) Operational ampli fi er (Op-Amp): It is used with different forms of feedback

and external circuitry to construct audio amplifiers, modulators integrated, filter etc.

(iii) Amplification:It is the production of signal of higher amplitude at the output

of an electronic system from small amplitude voltage input signal.


3/19

3

CHAPTER TWO

2.0. LITERATURE REVIEW

2.1. HISTORICAL BACKGROUND

The audio amplifier was invented in the year 1909 by Lee De Forest when he

invented the triode Vacuum tube. The triode was a three terminal device with a

control grid that can modulate the flow of electrons from the filament to the plate.

The triode vacuum amplifier was used to the first Am radio.

Early audio power amplifier were based on vacuum tubes known as valves and some of

and some of their achieved notably high quality e.g the Williamson amplifier of 1947-

1949.Most modern audio amplifiers are based on solid state devices (transistors such as BJTs,

FETs, and MOSFETs) but there still some who prefer tube based amplifiers and the valve

sound Audio power amplifiers based on transistors become practical with the wide

availability of inexpensive transistor in the late 1960s.

In early days of electronic, amplifier was achieved by the use of thermionic valves, which

telegraph signal before the introduction of diode. In 1948, this actually broadened the scope of

the amplifier.

In 1947 at the bell telephone laboratories Dr John William and Shockey, Dr John

burden and Dr Watter first demonstrated the amplifying action of the first transistor, whichwas lighter than valves and generates lesser heat and occupied little space. In the mid 1950s,

Field Effect Transistor (FET) was discovered and in early 1960s integrated circuit (I C) were

developed.

2.2 DESIGN PARAMETERS

Key design parameter for audio power amplifiers are frequency response, gain, noise, and

distortion. These are interdependent, increases gain often leads to undesirable increases in

noise and distortion while negative feedback actually reduces the gain, it also reduces

distortion. Most audio amplifiers are linear amplifiers operating in class AB. Since modern

digital device, including CD and DVD players radio receivers and tape decks already provide

a flat signal at line level, the preamp is not needed other than as a volume control and

source selector. One alternative to a separate preamp is to simply use passive volume and

switching controls, sometimes integrated into a power amplifier to form an integrated

amplifier.


4/19

4

2.3 FURTHER DEVELOPMENT IN AMPLIFIER DESIGN

For some years following the introduction of solid state amplifier, their perceive sound did not

have the excellent audio quality of best value amplifiers. This led audiophiles to believe that

valve sound had an intrinsic quality due to the vacuum tube technology itself. In 1972, Matti

Otala demonstrated the origin of a previous unobserved form of distortion transient

intermodulation distortion (TIM), also called slew rate distortion.


5/19

5

CHAPTER THREE

3.0. COMPONENT ANALYSIS

3.1 BLOCK DIAGRAM

The process of amplification can be explained with the following simple block

diagram illustrating the input device (microphone), pre-amplifier, power

amplifier and output device (speaker).

FIG3.1BLOCK DIAGRAM OF AUDIO AMPLIFIER

3.2. OPERATIONAL AMPLIFIER

The operational amplifier is a direct couple high gain amplifier which uses

feedback to control its performance characteristics. Internally, it Consist Of Several

Transistor Amplifier Connected in Series. Externally, it is represented by symbol

shown in fig.3.1

FIG 3.2 OPERATIONAL AMPLIFIER

Vp

Vn

Vi

Power

supply

Input

selectorVolume

controlPower

AmpsSpeaker


6/19

6

The operational amplifier is widely popular withanalogue circuit designer because of

its newly ideal characteristic.

The operational amplifier is capable of amplifying, controlling or generating any

sinusoidal or non sinusoidal wave form over frequencies

Form D.C to many mega hertz (MHZ). All classical computational functions are

possible such as additional, subtraction, multiplication, division, interpretation and

differentiation. It is useful for numerical application in control system, regulating

system; signal processing, instrumentation and analogue computers.

Functionally, as shown in FIG.3.2, the operational amplifier contains one output

terminal which is controlled by two input terminals. If a positive voltage is applied to

the positive inputs, the operational amplifier output will go to positive. Likewise, a

positive voltage on a negative input will cause the operational output to go to

negative. A simplifier model of the operational amplifier is shown in FIG 3.3 below

it indicates that an operational amplifier can be represented by a voltage source

which is controlled by two floating terminators.

Vp+

Vn_

FIG.3.3 SIMPLIFIER MODEL OF OPERATIONAL AMPLIFIER.

The two inputs are labelled positive and negative or non-inverting and inverting. The

positive (non-inverting) is in phase with the output while the negative (inverting) is

180 degree out of phase with the output. By connecting the resistor to the operational

amplifier shown in FIG 3.4.bellow, where we have the basic non-inverting amplifier

circuit. The basic inverting amplifier is shown in FIG 3.5.

AV (Vp-Vn)


7/19

7

FIG.3.4 NON-INVERTINGBoth inputs to the operational amplifier can be used simultaneously for different

amplifier circuit.

FIG.3.5 INVERTING

3.3 POWER SUPPLY UNIT.

The power unit is the stage at which the A.C input supply voltage is needed to power

the amplifier circuit by stepping it down from high voltage to low voltage suitable

for use and electronics. Most of the electronic devices and circuits require a D.C

source for their operation. Dry cell and batteries are one form of D.C source. They

have the advantage of being portable and ripple free. However, their voltages are


8/19

8

low, they need frequent replacement and expensive as compared to conventional D.C

power supplies, it is advantage to convert this alternating voltage (usually 220Vrms)

into D.C voltage (usually small in Value).This process of converting A.C voltage

into D.C voltage is called RECTIFICATION, and is accomplished with the help of:

(i) Rectifier(ii) Filter and(iii) Voltage regulator circuit.These element put together constitute D.C power supply.

3.4 TRANSFORMER

A transformer is an electrical device which is used in stepping up or stepping

down of voltage or current and for isolation purposes. It has no moving part and is

highly efficient. It uses the principle of electromagnetic induction and consists of two

coils which are laminated from each other by means of lamination sheet of high

permeable steel to prevent direct electrical contact. The two coils are primary coil

which is at the primary side of the transformer and the secondary side of the

transformer. When alternating voltage is applied to the primary winding pulsating

flux moving from positive maximum to negative maximum in every cycle is setup.

This pulsating flux induced e.m.f in the secondary windings.

Transformer usually step-up or step-down voltage depending on the ratio of theprimary windings to that of secondary windings. If the primary windings are more

than the secondary windings, then it is step down transformer, but if the secondary

windings are more than the primary windings, it is step up transformer. This is given

by the equation of transformer ratio as:

Where,

NP =number of turn of coil in primary side

NS=number of turn of coil in secondary side.

EP=e.m.f in the primary side

ES=e m f induced in the secondary side of transformer.

However, the primary coil is connected to the A.C mains supply of (240V, 50Hzor

220V, 60Hz) and the secondary coil as the output to another main circuit.


9/19

9

FIG.3.6 TRANSFORMER SYMBOL

3.5. FULL WAVE RECTIFIER

Electronic devices circuit require a D.C source for their operation. Dry cells

and batteries are one form of D.C source. Since the most convenient source of power

is the domestic A.C supply. It is advantageous to convert this alternating voltage

(usually 220-240V), to A.C voltage. The process of converting A.C voltage into D.C

voltage is called RECTIFICATION.

This full wave rectifier consists of an A.C input, a transformer, diode, and filter.

The transformer of the solid state electronic device and circuit fed by the D.C power

supply.

FIG 3.7.FULL WAVE RECTIFIER

When input A.C supply is on the transformer secondary end becomes positive and

negative alternative.


10/19

10

3.6 SMOOTHING CIRCUIT

The vary D.C output voltage from a rectifier circuit can be used to change a battery

but must be smothered to obtain the steady D.C required by the electronic gadgets or

equipments. The simplest way to smooth on output is to connect a large capacitor

called a RESERVOIR CAPACITOR across its value on a frequency of 50Hz

supply many ranges from 100 to 10,000 depending on the current and smoothing

needed.

The waveform of the smoother output voltage Vo for half wave rectification is

shown as a solid line in figure bellow.

The corresponding half-cycle of A.C during which the diode (D) conducts are

drawn dashed. The small variation in the smoothed D.C is called the ripple voltage.

It has the same frequency as the A.C supply and causes MAIN TUNE

The smoothing action of capacitor (C) is explained thus. During the half-cycle of

A.C when (D) is forward biased.

There is a current pulse which charges up capacitor (C) steps the load (R) supplied

with current by partly discharging through it, while its occurs, the output p.d Vo falls

until the next pulse of the rectified current top up the charge on (C). It does this near

the peak of the half cycle and so far every half of each cycle to the load current is

supplied by (C) acting as a reservoir of charge.The ripple voltage in a full wave rectifier circuit is smaller resulting in smoothing.


11/19

11

FIG3.8 SMOOTHING CIRCUIT WAVE FORM

3.7 STABILITY

The stability of a system is a measure of the senility of a network to variation in its

parameters. In any amplifier employing a transistor, the collector (IC) is sensitive to;

(i) B; since beta increases with increase in temperature.(ii) Base emitter voltage VBE: VBE decreases by about 7.5mw per degree Celsius.(iii) Icon (reverse saturation current); this double in value for every 10 degree

increase in temperature.

These three points caused the bias point in drift from the designed point of operation.

A stability factors is defined for the three parameters affecting bias stability. Forvoltage divider configuration, the stability are given

3.8. TRANSISTOR

A transistor is a three layer semiconductor devices consisting of either two N type or

one P type layer of materials or two P and one N type layers of materials. The former

is called an NPN-transistor, while the latter is called a PNP transistor. Both are

shown with symbols in Fig 3.9, where the three semiconductor layers (regions) are

collector, base and emitter.


12/19

12

(a)NPN transistor

(b) PNP transistor

FIG3.9 BI-POLAR JUNCTION TRANSISTOR

There are three normal operating states for BJT and this depends upon the bias

conductor applied to the two PN-junctions.


13/19

13

The state is when the transistor is in its ON-state, OFF-state and amplifying state. For

amplifying state, base, and emitter junction must be forward biased and base

collector junction must be reversed biased.

3.9. POWER AMPLIFIER

An amplifier main purpose is to take weak signal and make it strong enough

to drive a speaker. Power amplifiers get necessary energy for amplification of input

signal from A.C wall outlet to which it is connected. If the amplifier were perfect, all

of the energy the amplifier took from A.C outlet would be converted to output useful

(to the speaker). However, no amplifier is 100% efficient so some of the energy from

the wall outlet is wasted. The vast majority of energy wasted by amplifier shows up

in the form of heat.

3.9.1. PRINCIPLE OPERATION

The purpose is to receive a small electrical signal and enlarge or amplify it.The

operation of an amplifier circuit is base on the fact that the arrangement requires dual

power supplies. The amplifier circuit is power with 18V filtered D.C i. e. 9V at the

(+Ve) positive and 9V at the (-Ve) negative supply.

The negative feedback tends to stabilize also frequency response; this is called a non

p-inverting configuration of Op-amplifier. The differences of the input voltage pinand the feedback network voltage is differential input to the Op-amplifier. This

differential voltage is amplified by the open loop gain of the Op-amplifier and

produces an output voltage.

The potential differences between point A and B when the potentiometer is adjusted

will be coupled through a capacitor C to non-inverting input.

During the negative (-ve) half cycle Q1 conduct while Q2 cuts off presenting an high

impedance, the voltage is again build across loads but now inverting because the

circuit is complementary and that is why it is push-pull amplifier so that it give exact

replica of the input.


14/19

14

3.9.2 CIRCUIT LAYOUT


15/19

15

3.9.3 BILL OF MATERIALS

S/N COMPS TYPE VALUE QUATITY PRICE

1 R1 RESISTOR 220ohms 1 50


3 R3 RESISTOR 47killoohms 1 40

4 R4 RESISTOR 47killoomhs 1 40




8 R8 RESISTOR 2.2killoohms 1 50


10 R10 RESISTOR 100omhs 1 100

11 I C INTEGRATED CCTJRC4558 1 300

12 Q1 TRANSISTOR A73 1 200

13 Q2 TRANSISTOR C945 1 150

14 Q3 TRANSISTOR BD244C 1 80

15 Q4 TRANSISTOR CD110 1 100

16 Q5 TRANSISTOR BF871 1 150

17 Q6 TRANSISTOR M8306 1 100

18 C1 CAPACITOR 1000uf 1 400

19 C2 CAPACITOR 1000uf 1 400

20 D1 DIODE IN1401 1 50

21 D2 DIODE IN539 1 40

22 SPK SPEAKER 4ohms, 8watt 1 400

23 VAR. VARIABLE R B50k 1 100

24 T TRANSFORMER 12V 1 300

25 SW SWITCH On/Off 1 50

TOTAL=3450


16/19

16

CHAPTER FOUR

4.0 CONSTRUCTION AND TESTING

4.1 CONSTRUCTION

This chapter presents general information concerning the construction,

physical appearance and functions of the major components of the Audio Amplifier.

It describes various layouts, arrangement of the components and also the guideline to

be used during the construction.

The construction of this project involves the use of various components such as

resistors, capacitors, integrated circuit etc. Each component was tested before

insertion on a bread board for testing.

4.2 CONSTRUCTION OF THE CASING

The casing was made of plastic instead of wooded material; this is to prevent from

risk of fire outbreak in case of any short-circuiting. The plastic was shaped to form a

rectangular closure while sides were performed to provide ventilation for the

component inside.

4.3 ASSEMBLING OF COMPONENTSThe various components were assembled and soldered one by one using soldering

iron and lead. At the end 20watt audio amplifier ready to be tested.

4.4 TESTING

The first part of the construction process involved the measurement and testing of the

actual characteristics and respective value of the component used and comparing this

with theoretical details.

These following test were carried out with multi meter, testing for continuity of

resistor, diode, capacitor, transistor, and transformer.etc.

4.5 RESULT

Each stage was tested and they give approximate expectations. A signal of low

amplifier applied to the input gives on amplified output when connected to the

loudspeaker as expected.


17/19

17

CHAPTER FIVE

5.0 CONCLUSION AND RECOMMENDATION

5.1 CONCLUSION

The design and construction of 20-watt audio amplifier was indeed an interesting

experience for us, more so when we had pre-knowledge of practical works. The

amplifier can be put to use in lecture rooms where the number of students is large

and the voice of the lectures is not audible enough for those sitting at the back to

benefit from what the lecture is saying.

The construction of the audio amplifier by the students will save cost of purchase of

a similar audio amplifier from the market, since the both will be serving the same

purpose.

However, it must be noted that in the construction, there were some lapses due to

inexperience which may make the contract audio amplifier to be bit less in

efficiency to one constructed by professionals.

5.2 RECOMMENDATION

In order to gain better sound quality cable should be employed to transfer signalsfrom one point to another. In other words, it is the means of improving the stability

of power supply. The department should assist the final year student by building a

laboratory where students can construct their project, so that this will prepare them in

facing the challenges ahead of them in engineering field.


18/19

18

REFERENCES

Ajayi O,(2005).Electronics III unpublished Electronics, hand-out Department of

Electrical engineering, Federal Polytechnic ilaro, Ogun state, Nigeria.

Omolola,S.A, (2005). Easy approach to control Engineer system adex production

ilaroOgun state, pp.13.

TherajaB.L,Theraja A.K,(2003).A textbook of Electrical technologychand

andCompany Ltd, New Delhi pg 2229-2230, 2258-2259.

R .S. Sedha, (2002). A textbook of Applied Electronics S.chand and company

Ltd, New Delhi

http://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierallversions:cyrus

audio:productarchive:cyrus one.

Audio power amplifier design, peter baxandall, wireless world magazine, Feb

1979.

Circuit design modifications for minimizing transient intermodulation distort ion inaudio amplifier,MattiOtala, Journey of audio engineering society,vol20#5, June

1972.
http://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierall%E2%80%93versions:cyrushttp://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierall%E2%80%93versions:cyrushttp://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierall%E2%80%93versions:cyrushttp://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierall%E2%80%93versions:cyrushttp://cyrusaudio.com/product-archive/amps/i-intergrated-amplifierall%E2%80%93versions:cyrus


19/19

19

AKINWANDE MOSHOOD ABIOLA.docx

Documents

Transcript of AKINWANDE MOSHOOD ABIOLA.docx