Hello, I want to realize the second stage of this preamplifier (for line applications), and I'd like to know if someone knows if I can omit the switch
It seems to be as a potentiometer, or not?
I'm afraid I don't agree with you.
The gain is determined by the ratio of R95 (10K) and the resistance of R100..105 or R109..112 on the gain switch.
This has nothing to do with R91/R92.
Impedance on the base of Q27 is fairly high.