question about caps in an OCD

[ugly_guitar_guy]

Hey guys, this is more of a "why does this do this" question than debugging a build.

I was asked to build an OCD pedal this weekend, so I found this layout for it since using strip board was going to be the quickest option for me.



I had almost all of the components on hand already, but didn't have 3 of the right cap values. The input cap (C1) I ended up using a 22nf which I'm sure just allows a negligible about more bass signal through (right? higher input cap value=more bass signal?), and I didn't have the 220pf caps (C3 and C9) so I used two 2.2nf caps (which was the closes value I had on hand, and I realize it's not remotely close) just to try to get it working.

Obviously it's not quite "right." It sounds VERY dark, not terribly loud, and the gain is hardly affected when turned, but it does have a nice, sustaining drive to it. My question is what relation do those two 220pf caps have to the TL082 and what are the 2.2nf caps doing to squash the circuit? Thanks!

[Keppy]

Since caps pass high frequencies, the value of the cap sets the frequency for which the gain control is essentially bypassed. In other words, frequencies passed by the capacitor don't pass through the gain pot, so instead of a gain stage you have a unity gain buffer at those frequencies. By increasing the value of those caps, you've limited the gain in that circuit only to low frequencies, which is probably why it sounds so dark.

[ugly_guitar_guy]

Since caps pass high frequencies, the value of the cap sets the frequency for which the gain control is essentially bypassed. In other words, frequencies passed by the capacitor don't pass through the gain pot, so instead of a gain stage you have a unity gain buffer at those frequencies. By increasing the value of those caps, you've limited the gain in that circuit only to low frequencies, which is probably why it sounds so dark.

Awesome, thanks!

[ugly_guitar_guy]

Yup, put the proper caps in and it came to life.

I need to go to school for this crap... 

[Keppy]

I need to go to school for this crap... 

You ARE in school for this crap. I learned it here, or on Geofex or some other related site in the past year, and passed it on to you. Pass it on to the next guy!