can you alter the gain of an amplifier?

Well... you have made decisions which, imo, make it more difficult to achieve superior sound. By insisting upon using volume control in sources, i.e. CDP, you are locking yourself out of potentially far superior systems. You may have had success in using CDP as source and preamp function, but I found in many iterations with very fine CDP's that one can obtain far better sound by doing two things; use the CDP as transport and get an outboard DAC, and use a passive or active preamp with it. You are in no way assured to have superior sound simply because you are using the volume control of the CDP and the CDP's DAC. 

You may lose a touch of the most extreme refinement/cleanness going this route, but you will have an overall far higher end result in terms of most other parameters of fine playback. Trying to futz with amps is not a good solution, imo, and you will still have a largely compromised (not fully realized) system.  :) 

Adjustable gain in amp is very helpful to synergise with preamp or any input source with volume control.

Well, here's a trick you may really like.  Try using a 1:2 signal transformer. You can double the output voltage, while halving the input impedance though. I actually really like the sound quality, and it isolates the inputs.

Jensen Transformers is the usual benchmark for these.

Best,


Erik

Interesting suggestion by Erik. A number of people have reported here and elsewhere that they have found Jensen transformers of various models to have essentially no sonic downside, while a few have reported a slight loss of transparency.

A minor correction, though: If the particular transformer doubles the signal voltage (which would be a 6 db increase in gain) it would result in the preamp seeing the amp's input impedance divided by four, not two.

Regards,
-- Al

Now, these are some fine responses.  Al, your advice is ever highly informative and always a pleasure to read (in my posts and many others).  Doug, you turned me on to bridging the Pathos Classic amps I have a Cambridge Audio 840W which I'll probably do the same with as funds allow but the desire to NOT have an active preamp is largely based on money.  The expense of a really good preamp is a deal breaker for me.  I've had a few decent ones from Celeste (by SIM Audio), Perreaux, and Antique Sound Labs and all were easily bettered by not having them in the audio chain.  I believe I had a Theta Miles and then a Consonance Droplet 5.0 with these 3 preamps.  I do pay attention to cabling and had quality cables/cords on hand so the preamps were handicapped in this way.  The sound was just obviously more open and detailed without the preamps.  And I didn't hear a reduction of dynamics or bass weight without the preamps.  Both of these CDP's had plenty on their own.  Perhaps a top notch preamp would take my system(s) to the next level but I just can't afford it.  And Erik,  I like your advice.  I'll look into the Jensen Transformers.  Thank you all very much!