Why do we want to distortions?

+1 bigkids

I have heard at least three different model speakers on a Duelund cap upgraded PrimaLuna DiaLogue Premium HP (which incidentally was much higher resolving than stock), and they all sounded pretty remarkable to me.
These were all new only a few years ago.

There are some newer US made valve amplifiers I'd like to audition, when I'm ready to sell a limb or win lotto.

@atmasphere - thanks for the write up, very informative. Particularly the later developments with class D amps. I have owned just one class D and I've heard a few in my time, just nothing that was really really good sounding. I'm not trying to pick a fight, I'm just saying that I haven't been introduced to a class D that sounded as good as many of the solid state A, AB and valve amplifiers I have been able to listen to over an extended period of time. I am open to discovery, and I am eager to discover things have gotten better with class D.

Some of the best class D under $10k and under $5k that you have heard please? (I'm not likely to be in the market for a $25k amplifier, unless something drastically changes in my finances)

I have owned a hypex based class D amplifier from Nord Acoustics in UK. I think Nord’s amplifiers gives very good performance for the money. They now have versions using the newer Purify modules. You can specify OP-amp for the input stage. An example is the Nord Three SE 1ET400A MKII Dual Mono Stereo Amp for £1649 including Sparkos OP-amps.

"Nord Acoustics based in Cheltenham UK, design and hand-build world-class Class D Amplifiers that are changing Audiophile’s perceptions about Class D Amps. We take the very best designs from around the world and integrate them into our finished products."

I did see a video that covered the Purify modules and their 6.5" drivers. Admittedly I was more than a little biased against taking too much stock in the class D modules from prior experience with anything class D.
I still have the class D for the sub in my car system (in storage), previously I had found the mid-bass and upwards to not sound as musical.

I will go look at the reviews, and investigate this Nord amp, thanks.

This growing consensus about the appealing nature of low and even order harmonics and repellent nature of high an odd order harmonics is fascinating. From a biological standpoint it suggests the question, “how did this come to be“? If we step outside the arena of audio reproduction and look at acoustics and hearing by themselves I would say from my own experience that certain environments, rooms, auditoriums have better or worse “acoustics“. So do we encounter pleasing and displeasing harmonics naturally and could this be a foundation to explain how evolution tunes our hearing to prefer one over the other. I don’t know. I offer it as a hypothesis. Maybe others here with more expertise in acoustics can comment. I do know that if you take an acoustic instrument outdoors it becomes a mere shadow of itself sonically, likewise in an anechoic chamber. However in certain spaces the same instrument becomes much more pleasing. Could it be possible that this is the effect of these various types of harmonic distortion occurring naturally? Tying it back to evolution could the more pleasing acoustic environment also have been the better one for us to function in both predators and prey? @anders65 thanks for your comments which spurred this line of thought.

There are different types of feedback and I’m referring to traditional "loop" feedback. Degeneration is a bit different. But I think error correction is much better if that is possible in the design.

Correction is good. Degeneration does not tend to cause higher ordered harmonic distortion the way that loop feedback does. But one thing about loop feedback- it lowers the output impedance while degeneration raises it. So loop feedback is often used for that characteristic alone. But if you use it, you have to understand that loop feedback makes distortion of its own thru bifurcation, so you'll need a lot to minimize this problem. That's why I say 35dB is a good minimum amount. Any less than that (on a bell curve) and the distortion generated is audible as brightness and harshness added to the input signal.

I have owned just one class D and I've heard a few in my time, just nothing that was really really good sounding. I'm not trying to pick a fight, I'm just saying that I haven't been introduced to a class D that sounded as good as many of the solid state A, AB and valve amplifiers I have been able to listen to over an extended period of time. 

For a long time that was my experience too. The first class D amp I heard had me incredulous that anyone would buy it! But that was a long time ago and times have changed.

From a biological standpoint it suggests the question, “how did this come to be“?

Sine waves don't exist in nature. So its logical to expect that to detect the sound pressure of a sound that the higher orders would be the ones that the ear is tuned to listen for; they are far enough away from the fundamental frequency that they stand out much easier. In addition, the ear is tuned to be most sensitive at birdsong frequencies, likely owing the fact that birds will pipe up if they find a predator in the area- if you can't hear the birds easily you could wind up dead. Today we know the birdsong frequencies as the Fletcher-Munson curve.