Can't what you want be done with the modulometers?
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Onhwy61 -- well, that was sure stupid of me. You are essentially correct: the modulometer per se does not lower the gain, but there are jumpers in the pre designed to do just this -- it's been a long time since I looked at the owner's manual.
So THANK YOU for pointing this out, and it will probably fix my problem. Much appreciated
That said, I'm still very curious about the general answers to may questions, so would appreciate any responses.
I can't guaruntee saftey but you may be able to sub the 12AT7 for the much lower gain 12AU7. The 12--7 miniature twin triodes have the same pin out. The problem you might encounter is that while the voltage will lose gain, but the amperage pass thru goes up. I would still stick with the 5751 because it is just a better sounding tube regardless of it's lower mu of 70 affects the volume.
Other than that your choices are civil peaceful resistance. Or realistically a different volume attenuator which is what I think most preamps use to alter the volume of the amps. I think power amp gain is fixed and the preamp signal is what is indeed manipulated. The best way to do that is to buy a different preamp because buying a more sophisticated volume attennuator and having installed will cost a lot and lower the value of the pre unmoded. I know this is not the answer you wanted, but I also own a preamp with "gain from hell". The venerable ARC SP-6B which I just gave up on using.
BTW Almarg is a very good technical source, I would be still afraid though that a fixed resistor might flatten the sound. Just superstition but the resistor has to maintain the overall "caliber" of quality the rest of the pre has.
The jumper change made a huge difference -- in fact too much of a good thing. The Nagra jumpers attenuate a whopping 20 db. So now the volume control is between 12 O'clock and 4 O'clock. That's definitely better than before but....
Anyawy, Onhwy61, thanks again. Others, thanks for your additional posts.
I've done more research, and there seems to be a lot of disagreement about replacing 12ax7s with 12at7s or 12at7s with 12au7s. Or, similarly going from ecc83 to 81s....
Anyway, any additional thoughts on that would be most appreciated.
I had a Matisse fantasy preamp and it was much the same. I did experiment using -6db and -10db attenuation and this made a big difference. I ended up with a preamp using 6SN7's with a much lower gain and have been very happy.
I agree with Mechans it might be another preamp in the end that makes you happy. As he said modding a $9000 preamp is not the best idea. Many preamps use 12ax7 and 12at7 as did mine and yours. But if you don't need the gain you may try another preamp using 6SN7,12AH7, 5687 or even 12au7's.