Class AB amplifiers offer many advantages that make them the most commonly found designs in the mainstream hi-fi space.

For example, class AB amplifiers offer lower cost and cooler operation than class A designs, with some of the finesse and high fidelity, but with some of the punch and brute force power of class B designs and no class D drawbacks, in a relatively affordable package. You get a little bit of everything here, but only up to a point.

Class B topology is not good for audio because of non-linearity around the output device crossover point, resulting in crossover distortion. However, class B designs offer more power, lower weight and lower cost than a class A design of similar power. All designs are a series of compromises. Class B is intended where extremely high power output and efficiency are critical and some distortion is acceptable, like RF transmitters.

Class A amplifiers have no crossover distortion and offer the highest fidelity and greatest sonic performance. The flip side is that Class A designs are heavy and run hot, even for very modest power outputs, because they dissipate their maximum rated power, all the time, even with no signal.

Class AB amplifiers operate in class A up to a few Watts and then revert to class B for the rest of the power envelope. At lower levels, you’ll have the sweet sound of class A. You’ll have the punch of class B for dynamic swings and higher volumes. The more class A power on hand, the better the sound, because the more of the envelope is reproduced via class A operation, other things being equal.

Almost all consumer-grade amplifiers operate in class AB because of this topology’s cost-effective, high-fidelity nature. That said, most consumer amplifiers run very little class A power, sometimes only a couple of Watts, or less! The best results, as always, come from pure class A.