The sound of class A

December 21, 2019
 by Paul McGowan

I am often asked what’s the difference in sound between bias schemes like Class A and Class AB?

I understand the motivation of placing labels on circuits when making a product choice. Like tubes vs. solid state, or analog vs. digital. We like to characterize the qualities of technologies so we might put them in neat little category boxes.

The problem is, of course, that Class A and Class AB are biasing schemes that alone haven’t as much to do about how circuits sound as you might imagine.

Certainly, we could say that many Class A topologies generally are sweeter and without the character-changes-with-level some AB circuits have—and we would not be too far off the mark—but consider that many of us have never actually heard a pure Class A power amplifier.

In fact, what we think of as Class A is generally found in a small signal device like a preamplifier or output stage of a DAC, and that most power amplifiers are Class AB.

So, for most of us, our experience with the various classes of biasing schemes aren’t apples to apples, they are more like peaches to plums.

Methinks, in this case, most of our opinions are formed on the basis of what the audiophile myth-making machine would like us to believe.

From where I stand, biasing is but a very small factor in a complex world where everything has an impact on sound quality.

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