How important is S/N Ratio....?

Be careful as there is no defined way to measure this - it is the noise with respect to a "reference level". If you stick to pro audio gear than the S/N ratio on balanced outputs is usually referenced to 1.23 Volts.

If you use consumer RCA then S/N is often referenced to 0.316 volts or whatever the manufacturer "decides" (4 or more times less stringent)!

So the S/N specification on pro gear is significantly better than the same spec on consumer gear and on consumer gear it is misleading to compare specifications anyway!

Oh and by the way - the reason gear may sound different is that you can actually hear about 20 - to 30 db BELOW a noise floor (yes our hearing is quite good). So what matters more is the type of noise...if it is just thermal background white noise that is totally unrelated to the audio signal then you have a great piece of gear. If you have equivalently low levels of noise but when music is playing you have within it some correlated noise that follows with the music (harmonically or IMD related) then this gear will sound much worse (even if they both share the same "on paper" S/N ratio)

This is why gear sounds different and some gear has a blacker background where subtleties stand out a wee bit more. Remember our ears are like harmonic analyzers - they pick up vibrations that are cyclical in nature... so white noise is much more benign than correlated noise which has a specific frequency content and which changes in response to the music signal.

if it is just thermal background white noise that is totally unrelated to the audio signal then you have a great piece of gear

I thought I would add that this is why analog tape hiss or Vinyl road noise (apart from wow and flutter) is not a big deal - we hear the music through this provided it is random noise.

But let's ponder this.....if distortion effects what we hear......wouldn't the S/N....true measurement...measure the distortion present in the amplifier.

What I am saying is that S/N on its own is pretty meaningless(unless it is really bad and then it is a warning flag). It is just the background noise level present. This is why many specs are given as THD + N...

Just what does above quote mean in standard English?

I tried to say that noise at specific frequencies and that may be modulated by the music signal is far worse then just background wide spectrum random hiss...

This is why tape and vinyl works well even though it has a high level of surface or background noise.

Sorry for the bad english - I type fast and rarely check.

but when a lower S/N level can be quantified.....it has to have a relation to actual levels of distortion present....

Agreed but I think several replies here are simply trying to say that the link is not as strong as you suggest. Otherwise people with analog gear (vinyl or tape) would be very unhappy - and they are not! Distortion and Signal to Noise can be separate issues and don't have to be related. You can have one bad and the other good and vice versa. Of course in excellent gear both will be good.

Damping factor has been discussed many times on these forums and it is also misleading to pursue this number. I maintain that above a damping factor of 50 then you gain next to nothing. In fact, extremely high damping factors may be indicative of very high amounts of feedback and just like an amplifier with a specification from 10 Hz to 400 Khz I am wary of these kind of amps (Why do I need to amplify signals out to 400 Khz - surely it is better to get rid of this unwanted stuff). To me - there is danger in chasing excessive specifications which do not add anything to the sound quality but run the risk of making the amplifier less stable under difficult operating conditions....just two cents.

Oh and three things to look for in an amplifier:

1) More Power

2) More Power

3) More Power

...forgive me a cruel chuckle and a wink to Mini-Me!

Now we are talking. If you talk high quality components then yes there is a difference. This is much easier to appreciate than "specifications" in a brochure.

Eliminating transformers from the signal path (often non linear). Installing better quality capacitors - absolutely important if poor quality ones were used. (also bear in mind that some types of capacitors age and can dry out - so in this case it can make a HUGE/NIGHT AND DAY difference on a piece of gear that is ten+ years old) High quality AIR core inductors - absolutely. Resistors are usually less of a problem but wirewounds are recommended in high power applications.

Also just as a general rule - eliminating capacitors/resistors/inductors from high power paths (such as in crossovers) also helps a lot.

I have no problem agreeing with that - 100%

As for "More Power" I would suggest "Less Power".

Au contraire baby, More Power is More Mojo

I have had occasion to work with an F15 fighter in a flight testing project. Let me tell you, a full afterburner takeoff from a couple of hundred feet beside the runway is an awesome experience.

I didn't know there were some aeronuts here on A'gon. This is the World's best aerobatic pilot of all time - Jim Leroy.

BTW - Topgun is pretty awesome on HT with the volume cranked. However flying these things and cranking those g's is not all that pleasant - believe me I have first hand experience being up there...

You guys make me laugh though. F15 taking off. 135 db spl. Too loud. That is nothing. You guys are just wussies. Here I am at the airfield with my 153 db SPL system - just kidding ;-)