On too-much preamp gain
GENERALLY...where one runs his preamp-volume control depends on many things:
1. How much gain the preamp has;
2. The taper of the gain control;
3. How loud you want the music to be;
4. How much Voltage gain your poweramp(s) has, and
5. How sensitive your speakers are.
One can't do much with items 1 and 2 except replace the preamp. See below for possible tune-based solution for this.
Item 4 is one that I think most of us have wrong, in that amp manufacturers build most poweramps with (IMO) too much Voltage gain. Ten deciBels would be plenty; some have as much as 30. For every dB of gain you don't need, one must turn the preamp down a dB. Complicating the issue is that many of us think there's something wrong with a system that requires the preamp's volume control to be operated beyond, say, 'noon'. This is not true, in that, generally, preamps don't have too much distortion until they're clipping.
In fact, having 'too much' gain in the backend (= poweramps and speakers) amplifies the fixed noise present in 'all' preamps. If one has a noisier-than-average preamp and speakers with too-much sensitivity, your system will indeed have too much noise. One solution is to turn the gain contols on your poweramp(s) down to about half or less and turn the preamp volume up. What? Your poweramp doesn't have a gain control? Too bad. My poweramps, Atma-Sphere M60s, don't either, but A-S sells a tube-replacement plug that reduces the amp's gain about 10dB. I use one in each of mine.
If your preamp uses a member of the 12A
n7 family, one could try substituting a lower-gain version. For instance, people often use a 5751 in a position spec'd for a 12AX7 (the highest-gain member of the family, AFAIK), and there are 'U', 'T', and 'V' members, too, all of which have lower gain. AS FAR AS I KNOW, and I'm not thoroughly knowledgeable in this area, these tubes are, safety-wise, interchangeable, but that doesn't mean the rest of the circuit is designed for optimum sound quality. See
http://www.thetubestore.com/Resources/G ... ain-Factor
for more info. If I had your situation, I'd look for an inexpensive 'Y' or 'V' version to experiment with IF IF IF the original tube is a 12AX7 or a 5751.
Good luck; please let us know if you try replacing a tube.
