3 ms·

By slow do you mean high capacitance between base and emitter? I’m under the impression that even high power BJTs will be good out to 100 kHz. FETs are even b

By slow do you mean high capacitance between base and emitter? I’m under the impression that even high power BJTs will be good out to 100 kHz. FETs are even better I believe. Adding more components to the signal path degrades the signal slightly at best and introduces additional non-linearities at worst.

jeffbee 6y ago
I think signal path degradation is thinking that can only be applied to linear amplifiers, and Class D amps are anything but linear. They literally short the power supply into the load with nanosecond timing. The transfer function through all that lossy, distorting stuff in the output path is pre-computed and equalized out by the DSP. If I had been more clear about what I was trying to say, I wouldn't have said slow and fast. What I was trying to emphasize was that the linear power amps are optimized around a linear ideal of a transistor that never existed. By contrast, the Class D amplifier exploits the characteristics of the transistors we actually make today: high dv/dt, high di/dt, Rds(on) close to zero. There are fifty companies out there trying to outdo each other on these stats and the closer they get to infinity/zero, the better the output of these new amps becomes. There are fewer people out there any more trying to make transistors more linear in the linear region.
- amluto 6y ago
  You can always just use a big power op-amp. For some reason, audiophiles object to feedback, but any decent op-amp should give excellent audio performance. Power consumption and heat dissipation will be pretty bad, though. So you should go with class D.
  - hatsunearu 6y ago
    I tried designing a modest amplifier using op amps for the majority of the frontend. It's basically impossible unless you add a lot of stuff to buffer the opamp (which is why I wanted to use an op amp instead of discrete stuff)... big power op amps that have decent distortion exists, but not at their rated power. You get like 0.1% thd at typical levels needed to drive an output stage. And also thermal distortion will absolutely be an issue at that point.

jeffbee 6y ago

I think signal path degradation is thinking that can only be applied to linear amplifiers, and Class D amps are anything but linear. They literally short the power supply into the load with nanosecond timing. The transfer function through all that lossy, distorting stuff in the output path is pre-computed and equalized out by the DSP. If I had been more clear about what I was trying to say, I wouldn't have said slow and fast. What I was trying to emphasize was that the linear power amps are optimized around a linear ideal of a transistor that never existed. By contrast, the Class D amplifier exploits the characteristics of the transistors we actually make today: high dv/dt, high di/dt, Rds(on) close to zero. There are fifty companies out there trying to outdo each other on these stats and the closer they get to infinity/zero, the better the output of these new amps becomes. There are fewer people out there any more trying to make transistors more linear in the linear region.

amluto 6y ago
You can always just use a big power op-amp. For some reason, audiophiles object to feedback, but any decent op-amp should give excellent audio performance. Power consumption and heat dissipation will be pretty bad, though. So you should go with class D.
- hatsunearu 6y ago
  I tried designing a modest amplifier using op amps for the majority of the frontend. It's basically impossible unless you add a lot of stuff to buffer the opamp (which is why I wanted to use an op amp instead of discrete stuff)... big power op amps that have decent distortion exists, but not at their rated power. You get like 0.1% thd at typical levels needed to drive an output stage. And also thermal distortion will absolutely be an issue at that point.