Help with gain tone control

[franziscko]

Hi, i've build this 3 bands tone control, original schematic from Nuova Elettronica.
If you don't consider the first OP opamp, can you tell me how vary gain in the second OP amp? Sorry for my language...

 

[jan.didden]

I don't think you can do that, the feedback loop of the 2nd opamp is dedicated to the tone control, mess with that and you mess up the tone control.

You could put a potmeter after the 2nd opamp.

But what do you want to do?

Jan

 

[franziscko]

Thank you.
I want to increase gain, not decrease.
I don't know why, but i've some distortions with a gain of 7.

This is for a friend of mine, he want more gain.
I've removed R4 and used R2 - 100k and R3 - 680k and i have distortion.
I've made many others pre with OP amp but this is the first tone control.
Schematic is ok and pcb too, it isn't problem gnd or power supply.
Do you have some ideas?
Thank you for all.