Amp/Preamp Asylum

If you have a "dead zone"

23.125.184.79

Steve O

A

In Reply to: RE: Thank you, exactly. posted by 13th Duke of Wymbourne on February 12, 2025 at 12:24:48

Where both finals are in cutoff at idl, it's class "C" not "B" . . . Not good for audio. Almost all audio amps claiming "B" operation are really "AB" with idle bias current set low but high enough to prevent both finals from being cutoff simultaneously under real-world conditions of manufacturing and operation. It could be argued that true class B exists only at a single operating point where "AB" and "C" have an infinite number of points.

Follow Ups:

How do you classify taxonomists? - 13th Duke of Wymbourne 11:18:59 02/13/25 (1)
:)
- Hadn't considered that until now - Steve O 15:41:18 02/13/25 (0)
  Interesting how this amplifier class discussion arises every few years and involves some of the same persons each time. The basic amp classes were defined nearly a century ago . . .
RE: If you have a "dead zone" - morricab 06:37:17 02/13/25 (0)
However, that means the performance around zero crossing is very non-linear and will create a lot of distortion that is of a very obnoxious nature.

Look at the stereophile measurements I shared above. You can see the sharp discontinuity they have around the zero crossing. As one can imagine, this is essentially only high order dissonant distortion components. Even very low levels of these harmonics will audibly damage the sound.

As Tre was pointing out, even AB is not putting the bias in a very linear part of the transistors transfer function, which will also result in increased higher order harmonics.

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