KlasseAB

KlasseAB, often written as Klasse AB or Class AB in German contexts, is a term used in electronics to describe a class of audio amplifier topology that sits between Class A and Class B. In a KlasseAB amplifier, output devices conduct for more than half of the input signal cycle but less than the full cycle, typically achieved by biasing the devices slightly on. This biasing reduces crossover distortion present in pure Class B designs while avoiding the high quiescent current of Class A.

Practically, KlasseAB amplifiers use a push-pull pair of transistors (often complementary NPN/PNP) with a bias network based on diodes, a Vbe multiplier, or an active bias source. Feedback from the output helps linearize the transfer characteristic. Temperature compensation is common to maintain stable bias over varying temperatures.

Advantages include improved linearity and efficiency relative to Class A, with less distortion than straight Class B. The approach is widely used in consumer audio power amplifiers, guitar amplifiers, and other applications requiring decent fidelity at moderate power levels. The main design challenges are maintaining stable bias over temperature, controlling crossover distortion under heavy load, and managing power dissipation and thermal runaway.

Historically, KlasseAB represents the practical compromise that exploits the higher efficiency of Class B while preserving much of Class A's audio quality. It remains a standard configuration in many analog audio amplifiers, often complemented by negative feedback and robust cooling.