"chung" wrote in message
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No, there are Class A amps with noticeable hum and hiss, and there are
Class A-B amps that are close to dead quiet. It depends on things like
how much gain there is, how efficient the speakers are, and most
importantly, how well designed the amplifier is.
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The hiss is mostly coming from electronic stages *prior* to the power
amp anyway, if the volume control setting affects the amount of hiss.

Chung, my experience would agree with you on this. One amp I have is
dead quiet while the other, hooked to the same equipment and speakers,
hums. The second one which hums is designed by a well known engineer who
uses high gain as part of his magic in making his amps "musical". Once
the music starts, the hum disappears.
John