Active Baxandall in BSIAB2 makes a high pitch feedback

[juan_felt]

Hi everyone,

I replaced the tone control of the BSIAB2 with a 3 band active Baxandall. I managed to get the Baxandall to sound how i want it to, but there I get a feedback that increases when I turn up the Mids or the Highs.

Here are the schematics:

BSIAB2 http://www.generalguitargadgets.com/pdf/ggg_bsiab2_sc.pdf
Baxandall http://img.photobucket.com/albums/v165/rickydon/3band.gif

I inserted the Baxandall after C9 and before R17. I am using a TL072 opamp.

Any help will be very much apreciated.

Thanks

[DDD]

Maybe the reason is a positive feedback via inner parasitic capacitance of stomp switch.
It's possible to reduce this feedback:
- try add 560 or 1000pF to C1
- try 4,7nF instead of 2,2nF C13 (maybe C14, too)

[juan_felt]

Hi DDD,

Thank you for your suggestion. I tried it and the noise disappeared, so that solved my issue.

I still would like to know the source of the noise, do you have any idea?

Again, thank you!