Stereo audio amplifier / Alif Fawzuan Othman and Ahmad Assouffy Sallehudin

This report covers the design and implementation of a multi-stage stereo audio amplifier with its own voltage regulator, LED display, and digital volume control for each channel. The input can come directly from a CD audio player or similar device, and typical 8 Ohm speakers are driven. Digital volume control is implemented using a dipswitch, but this control device could easily be replaced by electronic components. The signal output is clean with no distortion up to certain audio levels, but some distortion occurs at higher levels. The unit is designed with five distinct components. The power supply provides positive and negative 12 Volts. The digital volume control is implemented using a summing amplifier, and there is one for each channel. Amplification is done in two stages, each of which is centered on Bipolar Junction Transistors. The first stage is a Common Emitter Circuit that functions to amplify the voltage of the signal. This stage has a large output resistance and can not effectively drive 8Q speakers. The second stage is a Class A-B Power Amplifier that provides the Common Emitter stage with a larger load, and is itself able to drive the low-resistance speaker with an acceptable current gain. LED output was achieved using multiple comparators, which compare the output to predetermined levels and light the LED’s when different levels are reached. Finally, the chosen design performs almost perfectly