Novice Driver: A minimalist 2-knob overdrive

[antonis]

R8/R9 value could be ten times lower followed by ten times higher C8 value.. 

[rankot]

Interesting and inspiring, as always!

[Fancy Lime]

R8/R9 value could be ten times lower followed by ten times higher C8 value.. 

Good point. Should have mentioned that if you use an opamp with a higher bias current (most BJT input opamps), the bias network impedance should be adjusted like Antonis suggested. With FET input opamps like the TL072, the values shown in the schematic work well and draw less current if you use a battery.

[antonis]

IMHO, it's more noise matter rather than impedance/current draw one..
(but, of course, for a simple overdrive configuration it could be an overkill..)

[Fancy Lime]

IMHO, it's more noise matter rather than impedance/current draw one..
(but, of course, for a simple overdrive configuration it could be an overkill..)

Hmm, true. I did not calculate it at first, I just stuck in what seemed OK and when I swapped to the 10k/22u combination, I could not hear any difference in noise from the circuit that wasn't completely swamped by the noise coming from the guitar.

Buy you are right, with the 100k/1u network, reactance is 8k at 20 Hz and 160Ohm at 1kHz. So increasing the cap may indeed be a good idea, especially if this thing is supposed to be used as a firt-in-line booster to hit another drive pedal or overdriven amp. There is enough space on the board here to use even a huge electronic although I doubt that it makes any sense to go higher than 100u. I would suggest a 22k/22u combination.

Thanks for the input,
Andy