Who tried Class D only to return to S/S or Tube

"Once the technology is there and they put that switching frequency way up higher, then and only then will they be able to filter the s**t out of it away from the audio band and leave a nice clean square wave, and only then will Class D have become of age"

Stereophile picture is about right:  1% of about 50V switched at 400kHz.  I’m not sure why it bothers you - you cannot possibly hear 400kHz.  Speaker will respond to average value.  There is distinctive possibility of tweeter modulating this wave with other frequencies, but this would be true only if tweeter’s membrane could move at 400kHz - not likely.  Also any effective radiation from speaker cable would require about 1/10 wave antenna that is 750m/10=75m.  I wouldn’t worry about that with few meter cables.  There is still possibility of cable to cable capacitive coupling but, because of shielding it would me minuscule amount further filtered by amp’s input filters.  There is some phase shift at 20kHz (about 20%), but it is usually the case of any amplifier bandwidth limited to 60kHz (my Rowland 102). Improvement in Mosfets speed will allows better initial linearity that is right now pretty good to start with.  Class D amplifiers suffer less delay (being one stage only) than multistage class AB amps reducing effects of TIM (resulting in softer sound).  Output impedance is also low by design, even without feedback.

Second generation of class D amps was better but I’m not even sure why.  Bel Canto’s Ref1000 got additional power supply caps and inductors.  That possibly reduced noise on the power cable (Power Factor Correction) but Icepower module used in both generations of this amp has line and load regulated power supply (uncommon in class A or AB amps).  My Rowland 102 is plugged into Power correcting Furman conditioner (big cap and inductor plus filters). Second generation of class D amps served one important task - it allowed some critics to remove foot from their mouth.

If top designers like Jeff Rowland, who is very sensitive to noise issues, don’t see any problems in class D or SMPS (that he uses in class AB amps), then I wouldn’t worry about it either and would judge it only on the merit of sound - it is the only thing that counts.  If it sounds good then it is good.

I think it comes down to the simple reality that audiophiles are in general a very insecure group. Many like to think that whatever components they have are "the best" and will go to great lengths to put down the choices of others in a senseless and futile effort to somehow prove the superiority of their choices, blind to the fact that there are no absolute "right" choices in a quest that is entirely subjective, and thus personal.

Most high-end audio manufacturers cater to this insecurity in a market that thrives on "mine is bigger, better, more expensive (thus sounds better) than yours"...

Class d seems to be the red haired foster child for those with deep insecurities, or perhaps, vested interests, as it gets kicked around all the time. Perhaps because it offers a level of performance to the masses at a previously unavailable low cost, taking away much of the snob appeal many of the insecure so value...For those without vested interests or insecurities, it has proven to be an exciting and fulfilling option for amplification. Excellent measured performance, high performance to cost ratio, small, light, energy efficient, plug and play without any finickiness, the list goes on and on. Never mind the fact that many have dumped their tubes and high dollar boutique ss for class d...No wonder people feel threatened!

Clearly, the reason there are so many different types of speakers, amps, dacs, etc., successful in the marketplace is obviously because tastes and priorities differ. There are many roads to audio paradise, none more valid than the next; we shouldn’t be so concerned and critical with the route others take but as fellow travelers, wish them well in their journey.

My assessment is the technology continues to improve in regards to power supply and switching frequency so even better sound is possible but when done right it already is hard to fault so how much it will matter practically remains to be seen.   I will keep mine for a long time I think and when time to replace technology will only be even better. Much like computers and other forms of digital technology.