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Designing an Audio Amplifier using Bipolar Junction TransistorsProject DescriptionThis is a design project and the simulation software used to simulate the design is Multisim. The aim is to design an audio amplifier and simulate it on Multisim. The design parameters are:1.The speaker load is 8 ohms.2.Audio frequency is human range i.e. 20Hz to 20KHz. 3.Only BJTs are to be used and Op-Amps are not allowed. 4.The test bench results should comprise of Audio Amplifier Power Output of 3.2 W with an Audio Amplifier Input of 150mVpeak and Audio Amplifier Power Output of 7.1 W with an Audio Amplifier Input of 200mVpeak.Introduction An audio amplifier is an electronic amplifier that amplifies low-power audio signals of signals composed primarily of frequencies between 20 hertz to 20,000 hertz, the human range of hearing to a level which suitable for driving loudspeakers and is the final stage in a typical audio playback chain. This audio amplifier amplifies audio signals with the help of many electronics component which are made up to produce such signals such as transistors, capacitors, resistors and many more.Design considerationsClasses of amplifier:
There are many different variations of amplifiers that cover a wide variety of applications, below are some of the more common classes of amplifier that can be used to drive audio outputs.Class A AmplifierThe most common type of amplifier configuration is the Class A amplifier. This is the simplest form of power amplifier and uses a switching transistor in the common emitter configuration. The transistor is biased “ON” so that it will continue to conduct during a full cycleof the input waveform, producing minimum distortion and maximum amplification. Figure 1 shows a Class A amplifier.Figure1Class B Amplifier
The Class B configuration uses two amplifiers in a “push-pull” configuration, one NPN and the other PNP. This means that only one transistor is only ever on at one time, using one to amplify the positive half cycle and another to do the negative half cycle. The advantage of this is that no current flows through the transistors when they are in a quiescent state (no input signal), therefore no power is dissipated in the output of the transistor when there is no signal present. This improves the power efficiency of the amplifier when compared to its cousin the Class A as less heat is dissipated during the overall cycle of the input signal and no power is wasted when no input signal is applied. This amplifier does however have one disadvantage, as both half cycles of the input waveform are amplified separately cross over distortion can occur. Crossover