What’s the difference for the listening experience when choosing between audio amplifier classes (A/B/AB/D)?
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The technical definition is that a class A amplifier uses a single element (tube or transistor) that conducts 100% of the time and amplifies the whole signal. A class B uses two elements that conduct 50% of the time, and each only conducts half the signal (positive and negative portions). A class A/B is a hybrid that uses two class A amplifiers but configured like a class B.
The differences between these are that class A is low distortion, low efficiency (at most 25%). Class B is high distortion and high efficiency (at most 75%). And class A/B is low distortion and moderate efficiency (at most 100%).
For decades, class A/B was used everywhere for audio power amps as it was the only sensible choice. Class A had its uses (often as a separate stage of the amp). Class B is basically a waste of a transistor or tube, so you don’t see it as much.
Class D operate entirely differently than tube and transistor amplifiers, but they’re lower distortion than any of the others and have peak efficiencies close to 99% and are cheaper at scale. So most devices use class D today, unless you have some other design constraints.
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