Arcam SA20

There are often two problems with hi-fi amplifiers. Class A, the traditional audiophile choice, uses a single power supply that runs at full power all the time, even when no signal is coming in. It is excellent for reproducing fine details at low levels, but has difficulty delivering extreme power when needed.

Class A/B, the most common class of amplifier, switches between two internal amplifiers, one for each half of the waveform. This is far more efficient, but often results in distortion, as the quiet details so prized by Arcam can be lost if there is a mismatch between the two switching stages.

Class G is essentially a hybrid amplifier that uses Class A specifically for quiet signals, but adds an additional power supply for the larger parts of the waveform when needed.