Mark Hammer's "contrafrizz" problems

[davemascera]

Hey all, i'm new here and this pedal really intrigued me so i decided to build it for my first.

Here's a pic from his original post of the schematic:



Basically, the problem i'm having is that the clean channel actually isn't showing up at all. If I turn down the distort pot, the entirety of the sound goes away because the only output i'm getting at all is fuzz (unless I turn the gain pot down,. The signal i'm getting out is definitely reduced as well. The crossover, and gain pots are working totally fine though.

I followed the schematic nearly exactly, except i just used a random pair of Ge diodes for the crossover instead of the 1n34a's and tl082's instead of tl072's...

I have a feeling this would have to do with a problem somewhere near the 2nd tl082, especially because past the .47 uf cap, i'm getting 0 voltage on the multimeter, even on the boost pot.. but I don't know if that's incorrect or not.

Does anyone have any ideas?

[davemascera]

Couple more things: I took out the second op amp entirely just now (and still left the 100nf cap 330 ohm resistor in place and got the same signal...) this is basically telling me the second op-amp is doing almost nothing

[Mark Hammer]

I'm confused.  Why are you using two TL082 chips?  One chip has the two op-amps needed for the circuit.  Or are you just describing it differently?

[davemascera]

I wish I was. This is unfortunate.

[Mark Hammer]

So you ARE using only one op-amp in each of the two chips?

[Kipper4]

Looks like the second op amp is used as differential amplifier. Mixing the guitar signal taken from pin 3 of op amp 1 (this also supplies the 4.5v to power the second op amp)
And the other distorted signal is going to pin 6 of the second op amp.
You can add more distortion on the output mixer op amp with vr1.
That right

[Fast Pistoleros]

me thinks he is seeing two chips and using two chips instead of following the pinouts 1-8  if that makes any sense ..not knowing how to interpret the schematic I am guessing

[davemascera]

Welp, here's the deal, I was indeed using two seperate op amps (i've actually never used one before and have no idea how they work). I was a little confused why they had the same name on the schematic.

I realized that I wasn't powering or grounding it. I removed it completely and used the single TL082 as intended. The pedal works basically fine now except for some hum, but that's easy to fix. Thanks so much. Awesome design and idea.

[PRR]

> confused why they had the same name on the schematic.

I'm confused now. The plan shows U1a and U1a. We might expect U1a and U1b (indicating that U1 has two units).

Mark can fix his copy. But HTH can he ever fix the millions of copies people take and re-post on strange servers?

[Mark Hammer]

Jeez Louise, how the heck did I miss that?  Good eye!!

Now I'm curious.  Was that MY error, or did John Lyons have that error in the original drawing that I modified?