Analysis of distortion sources in three-stage Class B audio power amplifiers

Abstract

Audio power amplifiers (APAs) are essential for high-fidelity sound reproduction, requiring high linearity and low total harmonic distortion (THD). Three-stage Class B amplifier architectures are widely used due to their efficiency, simplicity, and high output power capability; however, achieving low distortion across the entire audio frequency range remains challenging. This paper presents an analysis of distortion mechanisms in a conventional three-stage Class B audio power amplifier comprising a differential input stage, a voltage amplifier stage, and a push-pull output stage. Seven major sources of distortion are identified and examined. The frequency dependence of THD is evaluated, showing minimal distortion at low frequencies and a significant increase at mid- and high-frequency ranges due to the interaction of multiple nonlinear effects. The results provide practical insights for improving linearity and reducing THD in Class B audio power amplifier design.