What determines good distortion?

Lewhite is correct, I was confused. It's single-ended amps that produce the even order harmonic distortion versus push-pull amps which produce odd order harmonic distortion. I think my confusion is because MOST single ended amps are of the tube variety. However, yes, the Pass Aleph series are single ended solid state amps.

For me, distortion is distortion. It is never good. Some are just less offensive than others. SOme might even sound pleasant. But look up the definition of distortion.

If your goal is to reproduce the original as accurately as possible, it is NEVER good.

If your goal is to make the original better in some way that you desire (although concurrently less accurate), then some distortions might accomplish that. Distortions resulting from soft clipping versus hard clipping is a common and valid audio example.

Note that soft clipping is more common but not unique to tube amps and hard clipping more with SS amps, but some SS amps may also soft clip though I am not sure if any tube amps hard clip?

Better to be safe and avoid clipping altogether by not skimping on the power needs of your speakers in your room. Effects of clipping can be subtle and not easily recognized way before the point comes where you can clearly hear it! THis is a very common scenario that affects many unknowing listeners out there who cannot understand why their system does not sound as good as it should.

I'm sure there are some things that could be done to even the Mona Lisa to make it more appealing to some, but that would result in a reproduction that is distorted in some way but for good reason perhaps. Would that be wrong?

I'm sure there are some things that could be done to even the Mona Lisa to make it more appealing to some, but that would result in a reproduction that is distorted in some way but for good reason perhaps. Would that be wrong?

given the contents of your post, it would be wrong for you (& probably me as well 'cuz I agree with you that distortion is never even if it sounds good to one's ears) but would be right for many others.
Audio is so subjective & it depends on what the listener's objective is that there is no straight answer to your question. (of course, you already knew that! ;-) ).

Bombay,

I'm with you.

Distortion, whether good or bad, is determined in the head of the listener! So it's the listener who makes the only meaningful determination in the end.

Avoid clipping distortions though always! Oveer the long term at least, I doubt anyone with good hearing would prefer even subtly clipped sound using any amp technology to the alternative.

Distortion is distortion. When you hear or/and feel it, it's bad. Whether it is tube or ss doing it, I have low tolerance.