Phono Preamp Tube Rush

Between songs you hear LP groove noise.  Lift the tonearm and I bet it gets much quieter.  Then you will hear self-noise from input resistance and tubes.  

An good SUT can wonders, as they are mostly noiseless.  But not always.  If they use too thin of wire the resistance gets too high and becomes the main source of input noise.  The low-end Cinemag was like this (maybe they have since updated).

Mostly what you hear is noise from resistance, not tubes.  

if executed in the balanced domain you get a maximum of 6dB less noise

Actually, that's not true.  With balanced amplification you get 6dB more signal gain, but you also get 6dB more differential noise gain.  Overall SNR is the same.  

The benefit of balanced amplification is rejection of common mode noise such as power supply crud, and crap injected on both + and - inputs together (sometimes hum).  You get a better amplifier with higher overall performance, but noise floor from a differential source such as the resistance of a cartridge is the same.  

@lewm - Sorry I wasn't more clear.  Yes, I meant thermal noise from input resistance. 

The SUT in question had 3900 ohms on the secondary (thin wire), which generated quite a bit of noise, much more than I get from my JFET-based headamp.

And yes, you can use the ESR of a cartridge to perform a baseline minimum noise floor calculation.  You then have added noise (aka noise factor in the RF world) from the amplification (which you can break down by stage).  The first stage is by far the most important.  That's why I use special low noise matched JFETs for MC front-end.

Another good test for "tube rush" is to compare noise level between open and shorted inputs.  Most of the noise you hear open is from the 47k loading resistor.  Shorted, you hear the amplifier and tube rush.  

Yes, MC carts with lower ESR will produce less noise.

RIAA networks contribute noise, but it's not usually a problem, as the networks are implemented after one or two stages of gain.  Ten nanovolts of noise at the input of a phonostage has a lot more impact than ten nanovolts added somewhere in the middle.

You have to look at the entire picture here (as you hinted).  Every single component adds noise.  

It’s all relative. There will always be phonostage hiss, whether tube or solid state. The goal is to get it quiet enough such that it is lower than silent groove noise. How much SNR is enough?

I just tested my system (Piccolo2 - Cornet3 - Tuba) at full volume into an HP400 AC meter. The difference between a silent groove (my best is the Hi-Fi News Analog Test LP) and the tonearm up is 9dB. Perhaps not numerically impressive, but it’s like night and day listening-wise. The uncorrelated groove noise sounds way louder.

Forgot to mention, this is with a Dynavector 20XL MC cart (0.3mV) into 100 ohm loading...

SUT is the easiest way to get low noise input.  Works very well. 

I'm thinking all-tube may be possible using a pentode into a load of 10k or less.  Then again, microphonics will become the new problem...