I don't mind someone saying something is "better," IF he describes what
"better" means. For you and me, "better" means closer to neutrality
with more clarity. For a tubaholic, "better" means warmer, sweeter,
fuller, etc.
@viber6 For a tubeaholic, "better" means 'closer to neutrality
with more clarity'. Just so you know. That might depend on the 'tubeaholic' but all the ones I know are looking for neutrality and clarity that they can't get with solid state. This quite literally is what has kept Atma-Sphere going the last 46 years.
I mention this only so that you know that 'tubeaholics' are not so crazy as you seem to make out (I apologize if I'm putting words in your mouth).
I can identify why this is so: between 1960 and 2005 or so **all** amps employing feedback didn't have enough feedback for it to do what it is supposed to- get rid of distortion. In all cases, while suppressing distortion it also added some of its own. The distortion it adds is higher ordered harmonics and the ear perceives that as 'harsh and bright'; the 'solid state' sound. You can get a tube amp to sound like that too if you add enough feedback. In the cases of both tube and solid state the problem is insufficient loop gain; insufficient gain bandwidth product and poor phase margins (which, if exceeded, results in oscillation).
It is literally the brightness of solid state which is why tubes still exist! You don't have to know anything technical to understand this; its economics and nothing else.
Self oscillating class D amps offer a way around all this. Essentially you put so much feedback on the amp that its phase margin is exceeded and the amp oscillates. That becomes the switching frequency, and now you have a lot of feedback (more than 35dB) which then allows the amp to clean up the higher ordered harmonics generated by the feedback itself. A single formula, called the 'oscillation criteria' defines the loop gain, amount of feedback and oscillation frequency.
One thing about human hearing is that it is relatively insensitive to the lower ordered harmonics (the 2nd and 3rd in particular, which are treated in the same way). Another thing about the ear is the masking principle. The reason solid state has a reputation of harsh and bright with 'tubaholics' is the higher ordered harmonics are not masked by the lower orders as they are in a tube amp. Tube amps actually make more higher ordered content than solid state amps but they are smoother due to the masking principle; you can see how important this is if distortion is going to be present (and it always is)!
It turns out that the non-linearities of class D can cause lower ordered harmonic distortion to occur. These mostly are issues in the encoding scheme and distortion due to deadtime. With the high amount of feedback, the THD you get is at the same levels that you get with a very low distortion solid state amp but there **can** be an essential difference: the distortion *signature* can be more like a tube amp in that it favors the lower orders. Simply due to the lowered distortion, such an amp can be both very neutral and very relaxed- just like a tube amp (until it gets overloaded). Sort of the best of both worlds- an amp with excellent transparency, relaxed, musical presentation and acts like a true voltage source all at the same time.
