Anything as " fast" as SPECTRAL gear?

We've had a polarity switch on our preamps since 1989. Its only audible if the recording uses a minimalist microphone technique, like two mics to record everything.

'Fast' often refers to risetime or slew rate. Spectrals have always been very 'fast' in this regard. 100V/microsecond is generally considered 'fast'.

Most tube amps are 'slow' by comparison- 15V/microsecond being typical. Our amps are 600V/microsecond- IOW they have speeds similar to the best solid state. Tubes are not inherently slow (after all, if they were, color television would not have been possible...). But there can be design elements that can slow any circuit down.

'Fast' and 'slow' should not be confused with 'bright' and 'dull'; these are entirely different things, even if an amp that is 'fast' is also 'bright'. There are different reasons for these things!

Its not alchemy, but a designer does have to know what he is doing and it is the mark of a good engineer to know what is 'negligible' and what is not.

Beyond the alchemy part of your post, it is pretty much correct. Even a talented engineer will fall well short of possibility if he or she does not remain a student of the practice (or 'art'), especially that of the specific product and its goals. There is always something new to learn- I find that engineering/technical types that make the assumption that we know everything there is to know about audio are the same ones that have terrible stereos.

You have to have an open mind and in particular, be open to the fact that you don't know everything!!

Is "fast" a desirable attribute?

Yes. The human ear/brain system has a tipping point wherein if the reproduction of music is not 'fast' enough, the processing moves from the limbic system (emotional center) to the cerebral cortex (intellectual center).

But by and of itself speed is not the final arbiter- it must occur within an otherwise musical framework.

My understanding is that for the most part sonically, slew rate correlates to bass performance and rise time to treble. This is what I've been told by the tech who's worked on some of my amps.

Actually slew rate has almost nothing to do with bass, in case Al had not made that clear earlier.

Damping factor also has nothing to do with bandwidth, slew rate or risetime. However, A high risetime and slew rate can improve the effectiveness of the use of loop feedback, assuming the feedback parameters are properly worked out. So it may be that with higher risetime and slew rate, an amplifier with a greater damping factor can be built.

The thing is, no speaker needs more than about 20:1 for a damping factor- in fact if the speaker is over-damped, quite often a loss of bass impact is experienced (and is also measurable).

As Deep Thought was want to say: "Tricky."

If things are going well you will not hear 'speed' in an amplifier. If you do seem to recognize such based simply on highs and transient response, IMO/IME that is likely due to a coloration and not anything else (and often caused by trace amounts of higher ordered harmonic distortion).

Real speed is evident if the soundstage is deep and wide but not unnaturally so (this is because with speed comes correct phase response); the amp will be relaxed at high frequencies but obviously able to play them with a black background. I hesitate to say any more as so many other factors are involved/so many variables can exist...

^^ that has been my experience. The ear/brain system is the final arbiter and not enough is known about how we perceive sound to be able to go off of bench specs (which rarely have anything to do with human perceptual rules) to create a good design. Those who rely entirely on a goal of good bench specs tend to make lousy sounding equipment.

^^ Noise can obscure low level detail, which includes minor soundstage cues. So getting rid of noise should reveal more detail and more depth.

I hate to say this but when you hear a system that really is fast you'll know it when you hear it.

Things to look for: good decay (lots of it- good lower level detail), nice sound stage that is expansive rather than stuck as a little window right in the middle of the speakers (that 'wall to wall' soundstage can only occur if you have the bandwidth to prevent phase shift in the upper portions of the audio range), 'blackness' in the silent spots, but things like cymbals and strings have an effortless, relaxed quality...

Brightness is usually **not** an indication of speed (brightness is either a tonal coloration or the product of distortion); in fact a relaxed quality is a much better indication. Relaxed (even with the volume turned up!) yet excellent detail in the highs. The two go hand in hand if you have a fast system. Another thing- you might react more viscerally to the sound when there is speed. If you are tending to analyze the sound then its probably not fast.