Will changing gain affect frequency response?

Rodman - Absolutely no need to apologize. Those Fletcher Munson curves were new to me so you added to my little store of audio knowledge. Thanks for taking the time.

Czar - Interesting analogy.  I think I get your point applied to gain settings.

NOT talking about increasing the volume at the listening position

Increasing the gain by moving the jumper to the highest position

(keeping the volume the same at the listening position)
In some cases this gain change in a preamp/amps/cdp/dacs with links can be done buy a change in the negative feedback ratio loop.

And if you change the negative feedback, you change the things like the distortion, frequency response, stability, damping factor, slew rate and many more factors.
(In most cases the less the negative feedback, the more gain you have)

So what I’m saying is the "brightness" thing your hearing may vey well be the change in one of all of these factors, if these links apply to the negative feedback.

I know in a few Cary/Wadia dac/cd players it was done this way to have the user use the digital domain volume control used only it the top quarter of full, so the risk of "bit stripping" was minimalized.
Cheers George

In addition to how changing the gain of a preamp can change sound due to nonlinearity of the gain control, another thing to consider is where you achieve the gain.  For instance, I can change the gain on my phono preamp as well as on my main preamp.  I have tried it both ways and using the main preamp for increased gain sounds better than increasing the gain in my phono stage.

This discussion poses a question in regards to the Preamp-Amp gain/volume control. Should I run the amps [Mcintosh MC 60s] full out with the gain controls available on each amp and use a lesser level of volume on my preamp,[Zesto Leto tube pre]? Does trimming the gain on the amps give me less headroom when listening at higher volumes?

The output impedance of the Preamp is relatively low 150-250 Ohms to the input impedance of the amps which is 500K ohms. The preamp has two settings for gain, set internally, of 3 db and 12 db and came to me set at 3 db. I have very efficient speakers so the headroom of the amp and pre is sufficient either way. I rarely have the volume on the pre at 12, more at 10-11 max with the gain on the amps maxed out.

I ask this because I do fight brightness a bit and would like to optimally control the tone of the system towards a bit more mellow direction. 

The preamp has two settings for gain, set internally, of 3 db and 12 db and came to me set at 3 db.

Back to my first post, which everyone overlooked, how is this reduction achieved? Is it via the feedback network??
If so, this can influence the tonal quality, of where these gain setting positions are used, and they have nothing to do with the vc knob being high or low physical position for the same given volume.

Cheers George