A tracking-rail power audio amplifier was designed and partially implemented to deliver up to 100W into an 8Q load with very low signal distortion and high power efficiency. The design uses a class-A amplifier, known for its low signal distortion but low power efficiency (less than 50%), to amplify the audio signal. Class-D amplifiers, known for their high power efficiency (greater than 85%) but high signal distortion, provide a signal output that will serve as the supply voltages of the output stage of the class-A amplifier. Thus, the rails will track the audio signal, highly increasing the power efficiency of the Class-A amplifier. This amplifier can achieve a theoretical efficiency of 80%, but, in practice, it is closer to 70%.
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