Class-D amps - a different re view

I am elated to see in this thread manufacturers discussing merits -- or perceived issues -- with switching amplification. We consumers can only learn from these exchanges. I am however much less comfortable with veiled potshots about one's competition of the type:

"So into what impedance does this spec occur or is it 'marketing'?"

I appreciate a designer being proud of his own products, but there are more effective ways to demonstrate it. . . . than resorting to the 'lower' ground, which is not necessarily deemed a highly regarded marketing technique. Regards, Guido

Imho Martin Colloms should make apologies because he tried to disqualified class D amps by using pseudo scientific arguments that underlie his lack of knowledge. This is funny: What would Mr. Colloms do if class D was the only type of amplification? Kill himself? :)

Chris

Guidocorona, I was merely commenting on a spec that clearly was not possible as it was represented. I also demonstrated that with the math.

If you think I was taking a pot shot, I apologize. However, let me point you to a paper:

http://www.atma-sphere.com/papers/myth.html

The paper is about 5-6 years old, written long before class D was commonplace. The fact of the matter is that amplifier manufacturers have been placing specs like this before the public for years. I would prefer that the spec be placed in its meaningful context: that it is not speaker current but something else.

I've been watching the class D technology for some years as you must know if you've been reading through this thread (which has grown quite quickly!). Is it a threat to what we do? I don't think so, not because it might be better or worse, but for the simple reason that I am not going to be so close-minded as to think that nothing can beat what we do: there is no integrity in that.

We've been dabbling with class D for about 4 years and I plan to continue. As I've mentioned before, its a newer technology, and obeys price/performance curves that all new technologies follow. Right now we are in the middle of the curve. What that tells me is that we don't know yet where the technology levels off as it matures: it could go a long way yet! I apologize for my pragmatic outlook, but it is what has kept me in business for the last 30 years...

Atmasphere, Thank you for your contributions to this thread. I was discussing this thread with a friend a few days ago. We both agreed how much we appreciate your contributions and how you participate with a constant high level of courtesy and professionalism. You set a standard we should all strive for.

Ar-t - I have the smallest of the series and 23.5V on terminals. To deliver 5x more power they need voltage around 52.5V. I think it stays below safe level of 60V but agree with you that this might be of concern. I don't touch speaker connectors but with largest unit I would be concern about toddlers. Hypex is free from it.

As far as I know filter set at 65kHz has couple of chokes on one toroid (common mode chokes) and ouput capacitors. Frequency of this is in general fixed execept when Q is changing. Mine is listed at 65kHz at 8Ohm and 45kHz at 4 Ohm. Speaker impedance changes will affect frequency but it happens (if I remember) usually in lower frequency range. B&O lists idle frequency 400kHz-460kHz but for operating frequency they show 0-460kHz. I don't know what they mean - it cannot certainly be in audible range. Maybe they include audio signal in the spectrum?
So - there are some changes in the carrier frequency and therfore its attenuation. Audioband should have some phase shift - about 20 deg. increase at 20kHz compare to 1kHz. Is it common?

There is something different about highs of Icepower (might like it or not). Is it caused by limited bandwidth or dropping damping factor?

Some people called midrange of Rowlands 201 being magic and almost everybody likes bass performance but highs sound different.

There is no easy choice in design of amps. Class A has about 1/8 of efficiency and large power units are costly if not impossible. Class AB have nonlinear element in the output and require modesty in design. General problem is setting negative feddback to deep to get specs. THD for instance is difficult to hear below 1% but I would not buy class AB amp with 0.001% THD or very High DF. Sane designer would use the most linear elements setting bias current really high and would bring down thd only below 1% and then would limit input bandwidth to one amp had before feedback to prevent TIM. Unfortunately companies are racing for best specifications. I would advise to take specifications, promtly discart them and just listen.

Class D bypasses many problems and I know this is just begining. Comparing them to traditional amps is fair when is done to units in the same price range.