Tube Pre-Amp Question

Here is away to check it out....Play some music loud. Don't touch the volume control but turn off the source. How loud is the 'hiss'? If you can hardly hear it don't be concerned its very normal. If it is loud it could effect the 'black' background prized by many.

If it is loud at normal playback level I'd consider getting new low noise tubes, not necessarily a different brand unless you cannot get good low noise tubes of that brand.

PC's and IC shouldn't improve or mask this noise in any meaningful way.

you are probably hearing tube hiss, which is normal for a tube preamp, but it should not go up with volume.

I have the same VTL 2.5 preamp with a SS amp and it's dead quiet even if you put your ears next to the speakers and turn up the volume. The output impedance of the 2.5 preamp is 200 ohms. I've read here on Audiogon that the input impedance of the amp should be at least 10 times this number for a good match, which would mean 2000 ohms or higher. The amp I use has an input impedance of 22,000 ohms. I'm not sure whether this would cause the problem you're describing. If not, then it may be a bad tube(or tubes) or a ground issue.

I've been thinking of changing the tubes anyway. People have recommended Telefunken Tubes, and say it's night and day in performance when you do it.