AMZ Mini Booster/Mu Amp Bias Control

[Clint Eastwood]

Also, with your method, because you change the source resistance, you vary the current through the muamp, and this varies the output impedance.

With C2 series pot that doesn't happen?

You are right, it does change there as well, but differently. When you just raise the source resistance (without bypass capacitor), the gain goes down and the output impedance goes up.  With the C2 series pot, when you raise resistance the gain goes down and the output impedance as well. You basically turn the muamp into a normal amp.

[Steben]

I'm wondering why a keen very fine gain control is wanted on a muamp. I ask this because the muamp is designed to give more gain. If less gain is needed usually another circuit might be ok.