how to use gain control on a preamp

Maybe a silly question, but I just got a Magus preamp, paired it with a Belles 150a SS power amp and find it a bit bright with my speakers. Fellow who sold me the Magus said keep the right and left gain controls wide open. This doesn't work--too harsh in the highs. So I pull back on the gain and it keeps the detail, but where is the optimum?

I feel like I could fiddle back and forth with the 3 controls for quite a while before tame this beast. There are also gain controls on the speakers which has always been a problem figuring out. I try to keep that sort of in the middle (30 yr old Chicago Speakerworks 2-ways). Of course I should put some carpet on the wood floor and drapes up to calm things down too.

Well just wondering if there is some sensible process to follow so I don't wander around in the gain control wilderness.
i had an early belles amp, with the same pre (bought from House Of Hi Fi in St Paul). had the gain set at 3'o'clock..not open. played incredibly on celestion , chapman and several others. the room interaction (which you've noted)will dictate your final position.
I remember using the Gain and Volume settings on my Audio Research Sp 11 and found that I had the Gain setting at about 75% and used the Volume only after setting Gain..I also remember the older Audio Research Preamp units were supposed to sound better with the Volume at a higher setting,so I moved the Gain control lower to get the Volume control to aprox 12 o'clock high ( normal listening level ) ..Can't really say it makes any difference but I would suggest just set it and forget it....Not sure if that helps but????
If memory serves, I set the left/right gain so that the normal listening range of the volume knob falls in the 10:00 to 2:00 position.
I read an article several years ago that said pre amps were optimized to play with the volume set at 12 noon. this was not regarding signal to noise ratio but another variable regarding circuitry. sorry I do not have specifics
Changing a preamp's gain control often changes its output impedance, distortion spectrum, S/N ratio, and linearity. Each preamp design is different, you really need to experiment with it to find the position that you like best.
Sidssp I suspected it was kind of complicated interaction. I can experiment, but I'm glad to hear you all indicate that wide open is not preferred. You hear so many things around audio equipment it is nice to have this forum to gather some need perspective.

The pre amp was from a dealer and the Belles was off Audiogon recently.

I suppose it depends on the music too, so it is nice to have some control. I just have to get a handle on what I'm doing with it.

thanks much
Looks like to get the volume control up to the 10 to 12 o'clock position the gains need to be at about 9...which might seem to muffle the output some, but as it warms up it seems like a fuller sound...not so harsh. Also there is a fine amount of 3D effect with the gain turned down.

This is pretty much opposite of the advice given to me at the shop, but his solution was to buy a different amp--maintained it was a mismatch with the amps. Characterized the sound as "dry". I tried to match these components as people advised in another thread here and got the Belles because it has 100K input impedance and was supposed to provide a warm sound in combination with a tube amp.

So any more comments on setting the gain so low would be appreciated. Maybe it is just what sounds good to me, but if this seems like a mismatch, then...well anyone in the market for a Belles amp?

FWIW, I set the gain so that the volume control's setting is about 12 0'clock. The actual gain setting involved needed depends on the output of the cartridge (or other sources), the input sensitivity of your amp and the efficiency of your speakers.

But, FWIW consider I find the Belles amps to be less than tonally optimum even though electronically they will handle the high out-put impedence of the Magus. They certainly aren't going to add warmth. But then I don't care for most SS amps either - they are all too 'dry' for me, even when they are not plagued with grain or mid/high end emphasis.

Don't overlook tube selection in the Magus. I don't know what you are running, but tube selection in both the phono section (especially) and the line stage can make an important difference. You might try a couple of new production tubes in the line stage first, like the JJ6922 which has a warmer signature than many, and see if that makes a difference. If that floats your boat, you can then seek to refine your selection in NOS tubes if you want more.

Hope that helps a bit.

Have fun - its a nice little pre-amp.
Always trust your own ears. I am not saying the shop is wrong. It is just that different people have very different hearing and taste. What he likes isn't what you like and since you are the one who will be listening to your system day after day, you don't need others to tell you what is best, trust your own judgment.