Distortion In Power Amplifiers


Posted on Feb 6, 2014

The distortion produced by a typical solid-state Class-B power amplifier is shown to consist of eight mechanisms, all of which may co- exist and whose distortion products overlap to give a complex result. Methods for isolating each mechanism for study, and minimising its contribution, are given. If the avoidable distortions are designed out, Class


Distortion In Power Amplifiers
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-B amplifiers of unusually low distortion (Below 0. 0005% at 1kHz, 0. 003% at 10 kHz) may be designed as a matter of routine, and without significant extra cost. Such amplifiers define a distortion benchmark, and I have named them "Blameless" amplifiers. Considering the economic importance of audio power amplifiers, surprisingly little reliable information has been published on their design. Distortion in particular has been neglected, although it is the most variable feature of amplifier performance. You may have two units placed side, one giving 2% THD and the other 0. 0005% at full power, and both claiming to provide the ultimate audio experience. I investigated the origins of distortion in the period 1992-94, and determined that power amplifier distortion, traditionally a difficult and mysterious thing to grapple with, was the amalgamation of eight basic mechanisms, superimposed and sometimes partially cancelling, giving a complex result. I evolved ways of measuring and minimising each distortion mechanism separately, and the result is a design methodology for making Class-B or Class-A amplifiers with distortion performance so good that two or three years ago it would have been regarded as impossible. 0. 0008% at 1 kHz and 0. 003% at 10 kHz are easily obtained. The methodology gives reliable and repeatable results with moderate amounts of negative feedback; increases in complexity and cost are insignificant. Fig 1a...




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