Class D

No, what's more amazing, is how much of a troll you are, and that's been expressed by many here on Audiogon more knowledgeable it seems than you.

Oh George, I don't think you know the meaning of the world troll. I am sure I upset a lot of people here. It comes with the territory. They, like you, spew how you want the world to work or believe it works, I have the knowledge and experience from research to practical to know quite well how all this "audio stuff" works, right from recording tech all the way to small details in reproduction. That is the benefit of actually doing research (real research, like in a lab), and developing products instead of whatever you do.


Your position on Class-D is laughable. Atmasphere has explained in detail, at a simple level you can understand, why so much of what you say is wrong. I have explained, in terms simple enough for you to understand, what so much of what you say is wrong. Yet you refuse to take even 5 minutes to understand, thinking that reading an outdated effectively graph in Stereophile gives you more knowledge than people who have actually designed amplifiers, who understand both the math (mainly control systems theory), the electronics, and the practical implementation details.  But no, you are a greater expert than us, even though you can't even begin to explain the simplest details about your claim.

I would go back to making yourself useful trolling fuse threads, and let people who know what they are talking about talk about class-D. There are no doubt people on Audiogon more knowledgeable on some areas of audio than I am, but I expect the people you claim are "upset" don't fall into that category.  I am quite happy for Atmasphere or Duke to correct me, I would rather be shown wrong so others can learn, and mislead people. That is my character. What is yours?

Your a "fuser" which explains it all.

Every one knows "global feedback" is not a good thing in any amp, it’s a "sound sterilizer" and should only be used very sparingly if possible, just to clean things up a little, and preferably use only "local feedback".
Which won’t help your plight as you’ll need a stack of "global "feedback" that has to incorporate even the speaker output filter into it, to try to remedy this kind of phase shift problem down to 1khz 40 degrees out of phase, and 70 degrees!! at 10khz (in red). https://ibb.co/vvwzGV5

Actually 'everyone' does not know this about feedback and I think this is where your misunderstanding originates.

For many years, feedback did do exactly as you said. This isn't to say that 'every one knows "global feedback" is not a good thing in any amp' but it is to say that there was a known problem but no good solutions. This had been true for about 60 or 70 years, so you shouldn't (and probably won't) feel too bad about being ignorant of advances in the technology.

Now I've mentioned this before and I'll wager it went over your head. But nevertheless: It has to do with something called Gain Bandwidth Product. The math gets tricky, but in a nutshell you can sort of equate GBP to feedback as gasoline is to a car. When you run out of gas, the car stops, when you reach the limit of the GBP, you run out of feedback. This means that where ever that limit is, your feedback goes to zero.

You need GBP well into the MHz region to support feedback going up to 20KHz if you're going to use a lot of feedback. The more feedback you use, the more GBP you need to have. Well guess what? Nearly all solid state and tube amplifiers made up until about 15 years ago or so lacked the GBP to allow for a lot of feedback at higher frequencies. Put another way, this causes the distortion to rise as frequency rises.


To get around this problem most amps are measured at 100Hz; this sweeps the dirt under the rug. You don't see how the distortion is in fact higher at more critical frequencies like 5KHz. So at 100 Hz the feedback is adequate in almost any solid state amp, which is why they have a reputation for good bass, and this creates the idea that they must be OK elsewhere too. But we've been hearing the brightness and harshness for decades- in fact that is why tubes are still around.


Now how it works otherwise with feedback is if you add a little, it seems to help, you add more and the benefit diminishes, as higher ordered harmonics are added by the process of the feedback itself- and this is the cause of harshness and brightness in most solid state amps (and tube amps too- this is why feedback has a poor reputation). But this does not happen to infinity. It turns out that if you can get enough gain, if you run about 35dB of feedback this will allow for the circuit to compensate for the effects of the feedback itself. IOW, you'll have low distortion at higher frequencies.

Normally getting this sort of gain is hard, because your open loop gain is killed off by the feedback you have- and any power amp will need about 25 dB of voltage gain to be practical, and higher powered amps (which are likely to be used on low efficiency loudspeakers) might need 30 or 35dB. Well if you have 35dB to start with (and 40dB is better) that means you need at a minimum 60 dB of gain in the circuit open loop. That's a lot- and you run into something called 'Phase Margin' that limits how much feedback you can use before the amp goes into oscillation.

The semiconductors needed to make this sort of gain possible in a traditional design have not existed until fairly recently. But you have to know what you're doing even if you have the devices in your hand. One amplifier of 'traditional' design that actually does have the GBP and feedback to pull this off is the Benchmark. It is a very rare exception in this regard; obviously John Siau knows his stuff.


Class D amps have an advantage here though. If you give it so much feedback that it oscillates, you can use that oscillation as the switching frequency. All you have to be careful about is that it always find the same 'solution', the same switching frequency. But now at audio frequencies you have consistent feedback even at 20KHz; and this easily corrects for phase shift caused by the output filter (which is included in the feedback loop so as to allow the feedback to do its job).

This is all standard control theory. I don't expect you to know it because its clear you don't have an engineering degree. But you don't (and I'm sure you won't) have to trust me on this- its easy enough to find on the web if you cause your hand to move and search for it.

Really, do you really want to embarrass yourself yet again??  Calling me a fuser. What a laugh. Everyone who has read my posts here knows you are lying, but you are still upset I have shown you don't know how electricity actually works. Oh well.

As well, it is time you stopped this classless attack on Atmasphere who has been pretty much right on the money with everything he says. Your comments about "product protection" are something you should be embarrassed as an adult to make. Atmasphere is just too nice to say what he probably really wants to.