“Signal to noise ratio” and “dynamic range – capability”

Are “signal to noise ratio” and “dynamic range – capability” of an equipment proportional to each other ?

No, they are two different things, signal to noise ratio = rms signal power/ noise power, and dynamic range = Max power/ Min power. In a situation where the noise power is so much that it masks the Min power, the two could be related.

Are “signal to noise ratio” and “noise-floor” of the equipment inversely proportional to each other ?

Yes.

How do modern day tube preamps measure in these departments? Do SS preamps measure better or worse ? How does this affect the noise floor of the system ?

There is another parameter of importance, which you have not asked, this is call THD (total harmonic distortion), measured as rms signal power/ total harmonic distortion power.

As far as tube vs SS is considered, SS typically is better in all these departments (dont take the worst SS and best tube for comparison, BTW :-))

However one thing must be said in defence of tube, that is the tube harmonics may be more ear friendly compared to SS, and some audiophiles swear by it.

- Debu

square_wave schrieb:

How do modern day tube preamps measure in these departments?

There are some expensive tube preamps that measure superbly to the specs of SNR & THD. For example a tube preamp that I'm very familiar with has
Noise = 90dBa below 1V output for the line stage &
THD = 0.0005% at 1V output.
The tubes for this particular preamp are chosen with a highest degree of paranoia to guarantee the spec!
And, this preamp is dead quiet.
As the tubes age, you can hear the tube rush when you put your ear to the tweeter.

square_wave schrieb:

Do SS preamps measure better or worse ?

As Debu said, ss preamps do measure better. There are several people that I have read about in forums who switched from expensive, good sounding tube preamps to expensive, good sounding s.s. preamps & claim that the s.s. preamp is quieter & more dynamic.

square_wave schrieb:

How does this affect the noise floor of the system ?

I think that a well-designed tube preamp (that had, say, even SNR=85dBa at 1V output) corrupting or raising the noise floor of your system is the least of your primary noise issue! The noise generated from your corrupt AC power-line, the lack of proper isolation of your components, the lack of proper room treatment will do far more damage than a well designed tube pre. When you get all those other short-comings solved, then address the tube pre noise!

Thanks Bombaywalla and depu.
I keep seeing expensive tube preamps with a SNR ratios hovering around 75 to 85db while most good SS ones have above 95db.
I experience a lower noise floor and more low level detail with a tube preamp than with SS. So I was wondering what’s happening!
As Bombaywalla said, I guess system-synergy and setup is the biggest demon in most setups.

There is also the issue of the 'Colour' of the noise...

AAh.. i was just thinking of that as well.

Most tubes(Triodes)/Class A Amps might have a THD in the 80s but being even harmonic (primarily 2nd and 4th order) sound good , to the point of being even euphonic at times

While many SS and Pentodes (I believe.. am i right ?) have low THD but being predominantly odd (3rd,5th and 7th order) sound relatively harder (ear of beholder and all that applicable) but they are pretty accurate(er)..sic

But for a audiophile insising on neutrality an amp Low THD might just be a signal to audition while with an Audiophile seeking Primarily Musicality even at the expense of Neutrality, the former might just be the ticket to the Moon.