Class A operation means electrons flowing all the time [Gray].
No matter how loud or soft we play our music through these amplifiers power consumption is the same.
It follows that the higher the output power the cooler the amplifier or its active devices get. [Gray]
Electron tubes get hot for example by electrons striking at very high velocity the anode or plate thereby giving their kinetic energy to it. [Gray]
Before there is a transient an amplifier operating in class A is already full on, fully awake. No more average current is demanded from the power supply.
Such amplifiers, for example single ended electron tube or transistor ones with no negative feedback sound amazing.
With no negative feedabck there is no abrupt change between non distortion and distortion. So non linear or harmonic distortion tends to 0 as the signal tends to 0 and non linear distortion progressively or gradually increases as signal gets larger and larger. Just like nature.
Just like the very esoteric amplifiers used in mastering studios.
Great microphone amplifiers are also single ended class A. For example the Neumann U47 internal amplifier, the Pleiades V6 battery powered electron tube booster amplifier etc.
Reference:
Applied Electronics - T. S. Gray - MIT
See also:
Tubes vs Transistors (versus op amps), is there an audible difference? - Russel O. Hamm - JAES
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