Class D

It does not matter that Levinson used a bunch of air core coils (one thing does not make a whole).......what matters is the sound.

I did not say that it was the idea of  series'd air core coil output filters that ML used to get a steeper roll off as not to give phase shift down into the audio bad that made it sound bad.
The fact that a big company like Mark Levinson knew that it is a problem with Class-D, as this phase shift graph from output filters shows (red) https://ibb.co/vvwzGV5

That's why it's seems only fixable by moving the switching frequency and  filters way up higher so there's no effect of phase integrity down into the audio band, and the only way to do this is move the switching frequency up much higher to 1.5mhz and the filter as Technics did with the SE-R1 and hopefully with the SU-R1000 also.

And you can't fix it but throwing "more global feedback" at it, as that is a sound destroyer in itself.  The only way is the > 1.5mhz switching frequency, so the filter can do it's job without introducing phase problems down into the audio band.

The Levinson amp switches at 2Meg and it sounds bad.  For what reason?........who cares.  You buy it, you lose.  The AGD amp switches at 500K.....it sounds good.   For what reasons?......who cares.  You buy it, you grin.  End of story.....Everything matters.

That's why it's seems only fixable by moving the switching frequency and filters way up higher so there's no effect of phase integrity down into the audio band, and the only way to do this is move the switching frequency up much higher to 1.5mhz and the filter as Technics did with the SE-R1 and hopefully with the SU-R1000 also.

And you can't fix it but throwing "more global feedback" at it, as that is a sound destroyer in itself. The only way is the > 1.5mhz switching frequency, so the filter can do it's job without introducing phase problems down into the audio band.

Rubbish. Bruno Putzey's UcD module, which is quite old at this point (and predates NCore and Hypex), has less than 1 degree of phase shift at 20KHz. It switches at 400KHz and is self-oscillating, with about 40dB of feedback.

Rubbish. Bruno Putzey’s UcD module, which is quite old at this point (and predates NCore and Hypex), has less than 1 degree of phase shift at 20KHz. It switches at 400KHz and is self-oscillating, with about 40dB of feedback.

Serious!!! your rubbish, those things have always sounded crap in the upper-mid/highs, most probably because of all that global feedback, that’s why it’s considered an ok bass/sub amp.

The original UCD module had lots of feedback.....all around the output coil....The Ncore modules added even more feedback and the Purifi adds even more feedback.  Most people feel the Ncore sounds better than UCD and Purifi sound better than Ncore.  Read the reviews of the "super high feedback" Purifi amps.......they like them.  I am not a FAN of feedback....nor am I not a FAN.  There are lots of ways up the mountain.  Again, everything matters.  One amp with 500K switching could sound way better than another at 1meg switching.....or visa versa.....One amp could sound better with more feedback....or with less feedback.....it is not one thing......everything has to be done well.