@mtemur .. allow me to explain..
Yes, I am into vinyl that has significant distortion
Its probably that the playback has the distortion, not the LP itself. Almost any stereo cutter system employs a 30dB feedback loop around the cutter amplifier which includes the cutter head. That's a lot of feedback, and the cutter system has so much power that it can fry the cutter head itself before its making even 25% of full power. My Westerex system made 125 Watts but the head itself only could handle about 10 Watts. When you have feedback like that the distortion is quite low. So if you are seeing large amounts of distortion, its due to playback issues- its not on the record side.
I was merely questioning your comment that the SET does not measure as well as class D. If something does not measure as well, but it sounds better then I would question what good measurements mean. Maybe the SET measurements better correlate to what we perceive as the sound of real instruments.
Some of what they do does indeed.
Herein lies the wisdom of Daniel von Recklinghausen (engineer for HH Scott, an American tube amplifier manufacturer back in the 1950s and 60s) "
If it measures good and sounds bad, -- it
is bad.
If it sounds good and
measures bad, -- you've
measured the wrong thing."
Clearly we see here that THD
by itself is a good example of 'the wrong thing'. I've found over the years that a more important measurement that correlates much more closely with what we hear is whether distortion rises with frequency or not (if the amplifier uses feedback). Zero feedback amplifiers tend to not have distortion rising with frequency unless its a tube amp that has output transformer problems and if so that sort of distortion sounds different (less annoying).
The other thing I like to see is the distortion spectrum of the amplifier at 1 Watt, at 6dB below full power and at full power. In this way you can see how the amp changes with output power. What I like to see is that the 2nd and 3rd predominate (and are significantly higher than the the 5th and above) and the 5th is not more prominent than the 4th.
WRT to SETs what you see with them is that at low power they can be quite good to the ear. Once the power gets over that -6dB area though things usually change- higher ordered harmonics show up on the transients (where the power is); that distortion causes the transients to sound louder to the ear than the rest of the waveform; this causes the amp to have a false sense of 'dynamics'. At full power very few SETs are capable of the bass response they get at lower levels since the measurements show that the output transformer never has enough inductance to support that; the load line becomes elliptical. I know that sounds overly technical and geeky; what its saying is the amp can't make bass at full power before it overloads and this is also easily heard. The solution to this problem is to use a powered subwoofer.
These reasons are why SETs really should only be used with speakers of such efficiency that the amp never exceeds about 20-25% of full power if you really want to hear what they are about! This means that people using horns full range (as you are) are getting more out of their amps.
Its possible to get around these problems with a properly designed and built low power PP tube amp and not suffer any issues in the mids or highs (where SETs are supposed to shine). Nearly all the time when people compare SETs to PP amps, the comparison is invalid as the PP amp is usually several times more power, isn't class A, uses dramatically different tubes and so on. When you eliminate a few of these variables you find out by hearing it that there is a very good reason SETs went away (all of which are also measurable of course).
