More audio output power with less power consumption = higher efficiency and possible cost savings by drawing less current from the psu at all but maximum signal levels.
I see mention of some amazing DIY class B designs with vanishingly low distortion and high power. It would be really nice to see schematics, which should be possible since these are DIY designs, and presumably not commercial designs.
I wanted to correct a mistake I'd made previously. It seems the definition of class B operation does not necessary include a crossover notch caused by the output devices 'sticking' in a zero-conduction state for any period of time. It is technically possible to get everything lined up with microscopic precision so that the push side of the circuit turns on the instant the pull side of the circuit cuts off.
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But how is that achieved in real life, with devices that degrade over time, resistors that drift in value with heat, electrolytic capacitors that dry out with time and heat, etc? That's what would be interesting to know from Topping. My meager understanding is that it's much easier to get and keep a class AB output stage working well than a class B output stage.
Apparently Topping reps were confused at first, calling it class AB but then coming back and correcting themselves, stating it's class B after all. Lots of confusion.
That sales brochure says, "closer to class B than ever before." It doesn't say the output stage is out and out class B. It looks like very cold biased class AB, with at least a tiny amount of idle current drawn by both output devices at the waveform zero crossing.
What is leakage current, please? Where does that appear in this circuit? Thanks.
By definition. Class AB keeps more current going through the output devices, even when no signal is present. The advantage is that with no region where both output devices are in cutoff (not conducting current) there's no crossover notch to fill in. I'd read somewhere (still trying to find where) that negative feedback is powerless to correct crossover notch distortion, but that might be one of those things you read that aren't actually true. Who knows...
One thing I have heard from several engineering types is that with negative feedback in an audio amplifier, it's best to use either very little or none of it (if your amplifier circuit is linear enough that way, very difficult to achieve in real life) or use a LOT of NFB. If you use just a little NFB, higher harmonics are generated in the output waveform, which is not desirable. However, as more NFB is applied, all harmonics are suppressed more, including those higher ones. Pretty soon those higher fundamentals are buried in the noise floor and the main concern becomes stability, freedom from ringing, overshoot or oscillation.
Yes indeed it is! I've asked Amir twice to measure this B100 amp with a 10kHz square wave at a moderate signal level. No reply to that. I wish he would do that. I wonder, do all these wonderful little amplifiers measured here have exemplary output of a 10kHz square wave? No ringing, no overshoot, no slanting, no blunting of the leading edge or the trailing edge, no rounding? Or do we assume that the 10kHz square wave response of all these amplifiers is essentially perfect, so why bother? (I hate assumptions...)
Yes, because a class AB amp goes into class B when playing loud. That's exactly why it's not class A.
Well, there's a controversial statement. I'm not going to argue but I think I'll just quietly disagree. The challenge with applying great gobs of negative feedback to a non-linear circuit (like a class B output stage) has always been stability, overshoot, ringing, oscillation. I'd really like to know how Topping did it, and others would too, it seems. Or did they? How's the 10kHz square wave look?
OK, that's all. Thanks for your input, everyone. This Topping B100 amp is one very interesting product. Maybe it is exactly what Topping says it is, maybe it isn't.
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