Quote from: phatt on February 22, 2021, 12:39:19 AM
Opps,, Sorry I meant C4 which is .15 (150nF) This is just above the gain pot.
Then bass is wiped again at C11 .1 (100nF)
Small values there will wipe off a ton of Bass.
All 4 positions that I've noted need to be larger so rather than remove existing parts which might damage the PCB you can simply tack larger values on the track side of the PCB to test the outcome.
Maybe change one at a time so you know just where you are winning or losing mojo.
So that is C3,C4,C8,C11 can be larger.
C3 and C8 can be as large as 1nF.
As for C4 it's a tough one to guess as 470nF there might make the OD way too loud when S1 is closed. so suck it and see what happens.
As for C11 you may find that raising the value of R11 might help to wipe off extreme treble. Maybe try 4k7 or 10k. you will have to lift at least one end of that resistor.
Just search for opamp design principles, in this configuration the combination of R3 and R4 sets the gain and the value of C4 determines the bass roll off which of course raises the treble response of the circuit.
Same goes for the second stage;
This time R8, R10 and C10 set the gain and R11, C11 are switched which gives the treble boost.
If I remember,, in clean mode the first stage is lifted from ground Via S1 and that is likely not a very good idea,, others here might know more about that but to me it looks like it could be unstable.
Phil.
Thanks Phil,
I'll experiment with adjusting those caps in the simulator. I use a mobile app called Circuit Safari. Then in a couple weeks I'm going to have some free time to tinker with the amp. Many thanks for your time and the detailed direction.