New Class D amplifiers

@rsf507 

Not as yet. Still trying to follow this thread even though it seems to have taken on a life of its own. There are several I would like a chance to listen to first. Difficult to arrange.

D-Class are exceptionally good.  Lots of power, cheap. Here are two different reviews I did and are different prices.  One can be bought under $100, and the other around $600 as they Hypex amps.

And

@atmasphere: Your quote earlier:

There should be no difference at all! If you think there is, then you are convinced that we can't make the measurements for everything we hear (which, since about the early 1990s, we can) and also that the human perceptual rules that are shared by everyone on the planet are of no consequence, making things like deciBels irrelevant.

In the interest of my own learning, would you please point out which measurements correspond to what people hear? It would also be interesting to know how the type of measurement is performed and deemed to correlate to how our hearing works. Thanks.

In the interest of my own learning, would you please point out which measurements correspond to what people hear?

Sure- two measurements that have not got the attention they deserve- first, distortion vs frequency, which ideally should be a straight line or decreasing with increased frequency.

If the amp has problems with feedback due to insufficient Gain Bandwidth Product, the distortion will rise with frequency above a certain point (often between 1 and 3KHz). If this happens the amp could be perceived as bright due to how our ears perceive higher ordered harmonics and the Fletcher Munson curve.

The other measurement is the distortion spectra. Its not enough that the distortion be low. The ear has a masking principle; the way that tube amps sound nice and smooth is because they have enough 2nd and 3rd harmonic that those harmonics are able to mask higher orders. If those harmonics are insufficient, the amp may be perceived again as harsh and bright. This measurement is a bit open to interpretation as you have to know what you are looking at to be able to say how the amp is going to sound when you listen to it.

Quite often this last measurement is done with the fundamental at a low frequency - like 50 or 100Hz. If this is so and there isn't a measurement with the fundamental at 1KHz or higher then the measurement isn't all that helpful if distortion rises with frequency! IOW at a low frequency the distortion spectra might appear benign but above a certain frequency things could be considerably different.

So now you can see how an amplifier with 0.005% harmonic distortion might sound harsh and bright if those harmonics are not masked and the THD was measured at a low frequency- this can hide problems in the design. OTOH a zero feedback tube amp might have much higher distortion, but because it does not rise with frequency and the lower orders dominate, it might sound smooth and musical.

Class D offers a means to eliminate the first problem of rising distortion as well as allowing for a more benign distortion spectra.

@atmasphere , your thorough thoughts and comments are always highly appreciated.

How the measurements reflect the sound that we perceive? This is very interesting question somehow relating theory with practice. I still cannot put these two things together. For example, I have never heard a more complete, realistic and clean sound than my 5 watts SET tube amplifier gives (which unfortunately was broken due to a defective output tube). It has very high distortion including at high frequencies (up to 5%). I perceive no distortion on normal listening levels. On the other hand, i am not sure whether the distortion per se (as it is commonly defined in electric engineering) is that important. Again i perceive no distortion with my LSA GaN Voyager 350, neither at low nor at high frequencies, independently of speaker load. I think the frequency response is adequate.   I would not say that it has no soundstage or it is harsh. Apparently all is good but the sound is not alive, realistic and joyful. You see a wax figure, apparently all looks beautiful, but something is missing (you cannot make any real relationship with a wax figure). Perhaps , the problem is not that this and other amplifiers do not do something well, but that it doesn't do something that it should do? You may say that  second and third order harmonics are missing. But if there is no distortion, what needs to be masked?