11 ms·

It's actually class B that has the best performance. A lot of people say class B is bad because crossover distortion, but what they are actually referring to is

It's actually class B that has the best performance. A lot of people say class B is bad because crossover distortion, but what they are actually referring to is class C (the classic picture where a bit of the waveform is conducted by the top one and a bit of the waveform is conducted by the bottom one, with some flat spots in between) Class AB is bad because near the crossover, both top and bottom devices conduct and that actually causes an assload of crossover distortion. Properly biased class B precisely hands over conduction from one side to the other, making crossover distortion practically negligible. Class A is theoretically the best but you can get good performance, and perhaps even better performance than A with a properly designed class B amplifier.

hakfoo 6y ago
I'd always heard the problem with class AB was less that both devices were on, but that when it's switching off one side near the zero point, that action added noise. There were a lot of branded tricks in the dying moments of "stereo as a status symbol" (early 1980s) which tried to mitigate this. (Technics New Class A, JVC Super-A, etc.)
- hatsunearu 6y ago
  think of it this way: if you apply a sinusoid into a power storage, when the device (or the top/bottom device on its own) conducts 100% of the time, it is class A. When it conducts <50% of the time, it is class C. When it conducts >50% of the time (i.e. near the middle, both devices conduct), it is class AB. When it exactly conducts 50% of the time, it is class B. Turns out at the crossover point, when it's is class AB, you get something called gm doubling where the large signal gain goes up because both devices are conducting and therefore providing gain. When you're in class C (incorrectly called class B by noobs), no device conduct near the middle so you get crossover distortion in the opposite direction. In class B, you theoretically get near-perfect handoff which makes the crossover distortion minimal (at least compared to class A)
SomeoneFromCA 6y ago
This is the terminology Douglas Self uses. No one apart of him call class B class C.
- hatsunearu 6y ago
  Dude's right though. If you use the naming scheme everyone else uses, there isn't a name for the "class B" biasing that he talks about in that book. It's like a weird in between between class AB and class B.

hakfoo 6y ago

I'd always heard the problem with class AB was less that both devices were on, but that when it's switching off one side near the zero point, that action added noise. There were a lot of branded tricks in the dying moments of "stereo as a status symbol" (early 1980s) which tried to mitigate this. (Technics New Class A, JVC Super-A, etc.)

hatsunearu 6y ago
think of it this way: if you apply a sinusoid into a power storage, when the device (or the top/bottom device on its own) conducts 100% of the time, it is class A. When it conducts <50% of the time, it is class C. When it conducts >50% of the time (i.e. near the middle, both devices conduct), it is class AB. When it exactly conducts 50% of the time, it is class B. Turns out at the crossover point, when it's is class AB, you get something called gm doubling where the large signal gain goes up because both devices are conducting and therefore providing gain. When you're in class C (incorrectly called class B by noobs), no device conduct near the middle so you get crossover distortion in the opposite direction. In class B, you theoretically get near-perfect handoff which makes the crossover distortion minimal (at least compared to class A)

SomeoneFromCA 6y ago

This is the terminology Douglas Self uses. No one apart of him call class B class C.

hatsunearu 6y ago
Dude's right though. If you use the naming scheme everyone else uses, there isn't a name for the "class B" biasing that he talks about in that book. It's like a weird in between between class AB and class B.