New Class D amplifiers

@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? 

How the measurements reflect the sound that we perceive?

I described that above.

Since the ear uses higher ordered harmonics to sense sound pressure, its keenly sensitive to them since the ear has a +120dB range. If these harmonics are not masked by the lower orders (2nd and 3rd) they will contribute to harshness and brightness, since the ear assigns tonality to all forms of distortion.

That is why you don't hear it outright as breakup in any amplifier that isn't being overloaded. You sense it as tonality instead. For example, the 'dry' quality some amplifier have is due to their distortion signature, which audiophiles call the 'sonic signature' of the amplifier.

I don’t understand why Roon requires having your amp on all day, but putting that aside, going from A all the way to D strikes me as somewhat extreme for one who is used to the Pass. Why not look into a good A/B first? 

going from A all the way to D strikes me as somewhat extreme for one who is used to the Pass. Why not look into a good A/B first? 

The main reason AB exists is to reduce heat and power consumption, with some of the benefit of class A operation.

Class D allows a good designer to sidestep some of the reasons for class A operation in the first place- a classic example being that of crossover distortion. Most class D amplifiers are literally incapable of this kind of distortion. In addition, the distortion of the output section isn't made in the same way that it is in a class A or AB design. The result can be that the distortion the class D amp generates can be far more benign to the ear. 

I've heard class D amps that compare more than just favorably to a Pass Labs amplifier. These days its not about class of operation, it simply about the sound.