HIGH GAIN AUDIO AMPLIFIER SOUNDSYSTEM

ENGINEERING ELECTRONICS 1 LABORATORY

ABSTRACT

• This project aims to design any application that use transistor as amplifier or switch. So we come out with the idea to design a basic amplifier audio system that economical and simple.

• High Gain Audio amplifier sound system is an idea to provide an audio amplifier system that very economical and very simple in design yet still give you a good quality.

INTRODUCTION

AMPLIFIER

• Amplifiers can be very complex devices, with hundreds of tiny pieces, but the basic concept behind them is pretty simple. You can get a clear picture of how an amplifier works by examining the most basic components.

• The basic concept of an amplifier is a smaller current is used to modify a larger current. The input circuit is the electrical audio signal recorded on tape or running in from a microphone. Its load is modifying the output circuit. It applies a varying resistance to the output circuit to re-create the voltage fluctuations of the original audio signal.

TRANSISTORS AS AN AMPLIFIERS

• Transistor is a discrete circuit element. Since an integrated circuit is constructed primarily from dozens to even millions of transistors formed from a single, thin silicon crystal, it might be interesting and instructive to spend a bit of time building some simple circuits directly from these fascinating devices.

• Although nearly all modern digital ICs use a completely different type of transistor, the metal-oxide-semiconductor field effect transistor (MOSFET), most of the transistors in even modern analog ICs are still BJTs.

AMPLIFIER CLASSES CLASS A AMPLIFIER

• The class A amplifier has the highest linearity over the other amplifier classes and as such operates in the linear portion of the characteristics curve.

• As a class A amplifier operates in the linear portion of its characteristic curves, the single output device conducts through a full 360 degrees of the output waveform. Then the class A amplifier is equivalent to a current source.

CLASS B AMPLIFIER

• Class B amplifiers were invented as a solution to the efficiency and heating problems associated with the previous class A amplifier.

• Then we can see that each transistor device of the class B amplifier only conducts through one half or 180 degrees of the output waveform in strict time alternation, but as the output stage has devices for both halves of the signal waveform the two halves are combined together to produce the full linear output waveform.

• CLASS AB AMPLIFIER

• As its name suggests, the Class AB Amplifier is a combination of the “Class A” and the “Class B” type amplifiers.

• The advantage of this small bias voltage, provided by series diodes or resistors, is that the crossover distortion created by the class B amplifier characteristics is overcome, without the inefficiencies of the class A amplifier design. So the class AB amplifier is a good compromise between class A and class B in terms of efficiency and linearity, with conversion efficiencies reaching about 50% to 60%

• In other words, the conduction angle of a class AB amplifier is somewhere between 180o and 360odepending upon the chosen bias point as shown.

CLASS C AMPLIFIER

• The Class C Amplifier design has the greatest efficiency but the poorest linearity of the classes of amplifiers (A,B,AB).

• The class C amplifier is heavily biased so that the output current is zero for more than one half of an input sinusoidal signal cycle with the transistor idling at its cut-off point.

• In other words, the conduction angle for the transistor is significantly less than 180 degrees, and is generally around the 90 degrees area.

OTHER AMPLIFIER CLASSES Class D Amplifier A Class D audio amplifier is basically a non-linear switching amplifier or PWM amplifier Class F Amplifier  Class-F amplifiers boost both efficiency and output by using harmonic resonators in the output network to shape the output waveform into a square wave. Class G Amplifier  Class G offers enhancements to the basic class AB amplifier design. Class I Amplifier  The class I amplifier has two sets of complementary output switching devices arranged in a parallel push-pull configuration with both sets of switching devices sampling the same input waveform. Class S Amplifier  A class S power amplifier is a non-linear switching mode amplifier similar in operation to the class D amplifier.

PROBLEM STATEMENT

• Most of audio amplifier system nowadays are very expensive yet some of them didn’t give the high quality as their promise.

• Many of people are looking for simple kind of audio amplifier system and also more cheaper but still give them the good quality sound that can filling their room space without disruption from the noise that come from the audio amplifier system itself.

• That’s why we came with the idea to create the very low cost audio amplifier system that are very low cost but yet still give good quality in term of low of noise and high gain for voltage.

PROJECT OBJECTIVES

Below are some of project objective that we try to achieve from this project :

1. To create audio amplifier sound system that have low in term of noise.

2. To build an audio system that give you more high voltage gain

3. To create economical and less cost amplifier sound system

METHODOLOGHYDesigning A Basic Audio Amplifier (Class AB)The class A amplifier has a transistor that is biased with a voltage that makes it essentially stay turned on all the time. This single transistor handles the entire waveform both positive and negative. The class B amplifier uses two transistors. One handles the positive side of the waveform and the other handles the negative side of the waveform. Each transistor is in an off state until the waveform crosses over the zero point and then it must turn on. This takes about 0.7 volts so there is a small amount of time that the transistor is not amplifying the signal. This lag time at the crossover point can cause distortion. There is a way around this however, the class AB amplifier in the class AB amp the transistors are biased in such a way so as to never fully turn off. They are kept on by two biasing diodes which allow a small amount of collector current to flow even when there is no signal present. This means then that the transistor will be “ON” for more than half a cycle of the waveform but much less than a full cycle giving a conduction angle of between 180 to 360o or 50 to 100% of the input signal depending upon the amount of additional biasing used. The amount of diode biasing voltage present at the base terminal of the transistor can be increased in multiples by adding additional diodes in series. We can use just about any NPN and PNP transistors, just we need to make sure they’re within similar specification to each other. We are choosing to do the AB class amplifier because it can give us a better result in term of efficiency and linearity compare to class A and B amplifier.

We are using Pspice to do the schematic circuit drawing for our audio amplifier class AB and we add

another NPN transistor to get the better quality in term of sound and we also do the simulation to show both

voltage and current value for our circuit.

Parts list of components that needed :

2 – 2N3904 NPN transistors

1 – 2N3906 PNP transistor

1 – 47 uF electrolytic capacitor

1 – 470 uF electrolytic capacitor

1 – 100K ohm resistor

1 – 1K ohm resistor

2 – 1N4148 diodes

SCHEMATIC CIRCUIT DESIGN WITH CURRENT VALUE

SCHEMATIC CIRCUIT DESIGN WITH VOLTAGE VALUE

GRAPH