Hello all,
I thought it would be worthwhile to add to this thread as the unit does have a ton of gain that will severely limit use of the main volume pot. After reading through this thread and others, there has been some good information and some incorrect conclusions. I thought I would relay my experiences here to help future owners resolve the question of what to do with the excessive gain in a pre that they love.
First, let’s be clear what the circuitry is. ALL inputs, xlr (via input tube buffer) or rca get routed to the right and left input trim pots. The pots are a cheap Honeywell plastic potentiometer, 100kOhms. Recommended use for this pot from the Honeywell sheet is in ATVs, joystick controls, and more. Ruggedized for military standards. These Honeywell pots are directly wired to the two plastic potentiometer layers of the Alps 100 kOhm pots, which has a motor control. So you can use either the trim pots or the volume knob to control volume, or both. It doesn’t matter electrically, you just have 2 pots in series.
I have played around with the pots on the Cary, as well as digital attenuation. Re digital, some software driven attenuators are definitely better than others, but it seems like -10- to -15db is the limit where I don’t hear issues in volume matched back to back comparisons. Yeah, I know it shouldn’t be the case mathematically, but something is off. Besides, even -30 or -40 db digital attenuation isn’t enough to give you full use of the volume knob. So that isn’t the answer.
Playing with the pots is interesting, because you will quickly notice with volume matched testing that the balance trim pots are clearly filtering the signals. This shows up with low level information at all frequencies, but it is most easy to see with higher frequencies. Maybe a system runs a bit bright? Well ok, but the full spectrum loss of clarity and detail is not a favorable trade. Buy tubes that are rolled off on top, *cough* I meant warm sounding. 
Playing with the Alps volume pot gives similar results, but with less severity. The channel imbalance near max attenuation is a problem though, as is the high frequency filtering which makes the bass seem exaggerated.
So what are the solutions? I guess you have to decide what you want out of this pre. Do you use the headphones a lot? The input trim will likely be important unless your tubes are perfectly balanced. Input trims are useful for troubleshooting, but that is limited case scenario when it is also easy to just pull a cable. Only use the volume knob and you just want it to work better?
If you want it all I would look at replacing the volume and the trim pots with high quality stepped attenuators. Goldpoint,Khozmo, or others are good examples. Yes they are expensive. But your $6-8k amp deserves better than 3$ and 12$ pots. I put in a 24 step mono 100k pots in place of the trim as I don’t use headphones. If you do, maybe see if 47 step will fit.. First off, night and day improvement in clarity at all frequencies, you will sit up in your chair. Second, with high quality pots you will notice that the Alps isn’t exactly bad. If you do most of the attenuation with your stepped pots, then you can run the Alps from 12o’clock to full on with good results. In messing with this configuration over the last month, I would say that the less the Alps is in the chain, the clarity improves but with diminishing returns. My next step will be to replace the Alps with a 47 step attenuator and call it good. The upper range of the 24 stepped input trim is just a teensy bit limiting in my system.
Motorized volume knob mandatory? Well there are solutions depending on the attenuator you choose, but they are expensive. I would go this route if you plan to keep the pre for as long as you can. I haven’t decided what to do yet, I might see if I can use the existing RC design and fabricate an adaptor for the new attenuator. We’ll see.
Hope this helps. Yes, get a professional to do the work and the usual disclaimers. I have no knowledge of EE or circuit designs, these conclusions are my own experience and you may get different results. Make modifications at your own risk.
