That "tube sound" and power ratings

How things distort is one aspect that varies with different amplifiers but is only one aspect of performance of sound.

How much power is needed to drive any particular pair of speakers is mostly a function of recording quality and SPLs (how loud you listen).

For optimal performance, it is almost always a good idea to have more power than needed rather than less.

Clipping is always public enemy #1 when it comes to amps and speakers. you want to avoid clipping at all costs in that it will only compromise the sound quality to various degrees.

The only way to avoid clipping is to have more than enough power than will ever be needed to drive the speakers OPTIMALLY.

Having said that, optimal performance is a good first goal but alone does not assure "sound quality". Personal preferences come into play when talking about what sounds "good" . Optimal performance is always a good thing but alone does not assure you will like what you hear, though the chances are best that you will for sure.

So always strive toavoid clipping no matter what first. Then decide on your favorite flavor of sound from there.

Further, the topology of the circuit says a lot about what sort of distortion it will make. For example, a push-pull amplifier with a single-ended input will make primarily 2nd ordered harmonic distortion, but will also have some of the 5th. If the amplifier is fully differential and balanced, the primary distortion product will be the 3rd harmonic.

If negative feedback is applied whether tube or solid state trace amounts of the 5th, 7th, 9th and beyond will be added.

At any rate loudspeaker efficiency is important when dealing with tubes, as tube power is more expensive than transistor power! Its important with any system to avoid distortion but in fact distortion is the name of the game as the human ear translates distortion into tonality- this is why transistor amps tend to sound bright, even though the distortion is very low, what distortion is present tends to be the odd orders, to which the human ear is particularly sensitive.

A lot of push-pull amplifiers will actually make more distortion below a certain power level, so for those amplifiers its helpful to have a speaker that is a little less efficient, so the distortion is happening at a lower level and is hopefully less noticeable. But this is why some amps seem to lack detail at lower power levels.

There is definitely more to this than meets the eye!

Clipping is the most common and pervasive form of distortion in most cases.

Unless you only listen at very low volumes, there is a very good chance that clipping and related forms of distortion will come into play and degrade sound quality in ways that might not be very apparent.

Its not that hard to avoid clipping. Just do not use an amp that is underpowered to drive the speakers. Use more power not less as an insurance policy. Most speaker manufacturers understate the power needed to drive their speakers optimally in order to keep markets open.

If your speakers are even moderately efficient, that helps a lot in terms of choosing an amp that is up to the task.

If you will only listening at low volumes, then none of this matters all that much. The world is your oyster and almost any amp/speaker combo might do.

Once teh amp is up to the task of driving the speakers OPTIMALLY, then you are in a position to determine what other remaining forms of distortion to choose among based on what you hear.

Public Enemys (of good sound):

1) room acoustics
2) amp clipping
3) choose your poison

Note that most tube amps (and some SS amps) soft clip which is why fewer watts seem to go further. But the clipping still occurs, though it will take more volume before the results become clearly unpleasant. But any clipping is distortion. You loose dynamics whic is what adds the excitement to a lot of music. If you don't care about that and only listen to small ensemble chamber music, you might be fine, but eventually you may realize what you are missing and look elsewhere.