Egodriver squealing

[Hyatt]

Built the Egodriver, and its squealing and feeding back like crazy.  My soldering iron was too hot so it took off the pos pad of C10 and also the led.  I removed C10 and soldered wires to the top side of the board for the led.  Lights up, gets bypass, OD works but theres an overpowering squealing and chaos going on.  It can be controlled by the gain pot.  Could be a cool noise device but I really wanted an OD.  Any suggestions?  I remember I asked about C10 previously, I think it was fine to leave off.  Is my gain pot broke maybe?  Anything I should try? 

[ckyvick]

Can you try to put c10 back in and use the leads of the cap(or bare wire) to jumper the connection? It might be the problem.

[Hyatt]

hey thanks for the reply.  I tried jumping the positive pad of C10 to the grounded leg of R15 and it helped.  It won't squeal anymore if the gain knob is down, but as you turn it up itll start feeding back and when its maxed it goes into a low, rumbling self oscillation.  Might make a good Atoner but this is not the time for that.    Show on saturday and id love to use this thing. 

[Hyatt]

Still no luck. Remelted the joints, cleaned the board, checked wiring.. Lesson learned: if it aint' broke, don't fix it, cause you'll break it.

[madbean]

Could you have put the wrong value resistor in one or both of the amps? I don't have the schem in front of me, but IIRC there's an 18k before the gain pot and a 220k in the second amp. A wrong value in one of those places could definitely cause oscillation if it's too high.

[Hyatt]

Doublechecked the values, everythings good.  It was working great before I tampered with it.  The gain pot was wired backwards so I reversed that, I wanted to change the color of the led and change the electrolytics to higher voltage ones.  At some point I must've fried something (as well as taking the pads off the 10uf and led).  I swapped out the op amp too with a spare I had laying around and the sounds/oscillations changed on the new op amp but its still messed up.  I lost my audio probe, that'd be very helpful right now.  Hopefully I can salvage this before tomorrow night.

[ckyvick]

do you have a resistor you could replace the pot with to see if that is the problem? have lug one connect to one side and lugs 2/3 to the other side to simulate the pot being maxed out

[Hyatt]

I'm not sure if i have a 1m resistor but i should have something close laying around.  First i'm going to go to radioshack and get another op amp.  Somehow throughout the night it got a little better.  Now it sounds normal for about the first 25% of the gain knob, 25%-75% it squeals, last 25% it rumbles.  Very strange.  I'll be back.

[Hyatt]

Found it.   Soldering the lead to R15 wasn't the right connection, needed to be R14.  Works fine now.  Thanks for the help.  It sounds good.