A two-watt transistor audio amplifier

For low distortion, power transistors should be driven from a low impedance source. Thus an emitter-follower driver has definite appeal. A further advantage is that the driver transistor may be direct coupled to the output transistor. This paper describes the basic design method for this circuit and illustrates its performance. Important considerations such as stability, transistor interchangeability, frequency response, and distortion are discussed and typical measurements shown. The features of this circuit are: good stability and the facts that transistor parameters are noncritical, no bias adjustments are required, frequency response is flat over the audio range, and distortion is low.