Author Topic: Problem with custom overdrive circuit  (Read 461 times)

josephfra

Problem with custom overdrive circuit
« on: July 28, 2022, 06:50:34 AM »
Hey everyone, I recently made this circuit on a breadboard and it worked pretty nice.


So I ordered a PCB with the same design, but whenever I activate the pedal I get no output at all regardless of where the DPDT switch in the schematic is set. The only noise I do get is a very cool but also very-not-what-I-wanted oscillation sound if I touch the PCB in the right places...

What do you all think? Is the issue a result of poor circuit design or could there be some other troubleshooting steps to take? The only thing I've thought to do is check the continuity between every single component of the signal path, which seems to be fine.

antonis

Re: Problem with custom overdrive circuit
« Reply #1 on: July 28, 2022, 07:18:33 AM »
Most possible is wrong DPDT switch orientation or wiring.. :icon_wink:

Either flipped 90o or reverse lug wiring..
(e.g. not simultaneously activated SAT1 & SAT2 lugs 1 & 3..)

Provided correct orientation, short (via an aligator clip or similar) lugs 2 to bypass Tones and locate the issue..

P.S.
Just curiosity: How is TL074 unused amp wired..??
« Last Edit: July 28, 2022, 07:26:52 AM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

niektb

Re: Problem with custom overdrive circuit
« Reply #2 on: July 28, 2022, 08:02:06 AM »
slightly off-topic but maybe related: I think D1 and D2 should go to ground, not 4.5V

josephfra

Re: Problem with custom overdrive circuit
« Reply #3 on: July 28, 2022, 08:19:17 AM »
Most possible is wrong DPDT switch orientation or wiring.. :icon_wink:

Either flipped 90o or reverse lug wiring..
(e.g. not simultaneously activated SAT1 & SAT2 lugs 1 & 3..)

Provided correct orientation, short (via an aligator clip or similar) lugs 2 to bypass Tones and locate the issue..

P.S.
Just curiosity: How is TL074 unused amp wired..??

The DPDT seems to be wired ok. I shorted the lugs like you said and I'm now just getting static noise that sounds slightly quieter when I touch the guitar strings. Could this be a sign of anything in particular?

The unused amp is just soldered to the board but not connected to anything.

slightly off-topic but maybe related: I think D1 and D2 should go to ground, not 4.5V

Oh ye, I had them going to 4.5V before when there was an opamp gain stage after it but neglected to change it. Not sure if it'll actually affect anything other than the amount of clipping?

antonis

Re: Problem with custom overdrive circuit
« Reply #4 on: July 28, 2022, 08:19:37 AM »
slightly off-topic but maybe related: I think D1 and D2 should go to ground, not 4.5V

As long as 4.5V point is cosnidered AC ground (due to C11) it's OK..
(although I totally agree with you..)

edit: As it is, D1 might make LEVEL-SAT pot crackly..

What puzzles me is the purpose of U1.1 buffer..
It could be omitted (together with C2 & R6) and implement an op-amp with half the pins of TL074 for the whole circuit..
« Last Edit: July 28, 2022, 08:32:52 AM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

antonis

Re: Problem with custom overdrive circuit
« Reply #5 on: July 28, 2022, 08:26:36 AM »
The unused amp is just soldered to the board but not connected to anything.

"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

antonis

Re: Problem with custom overdrive circuit
« Reply #6 on: July 28, 2022, 08:47:23 AM »
For future implementation.. :icon_wink:



P.S.
LEVEL-SAT pot is intentionally omitted..
(I let you guess the reason ..) :icon_wink:


« Last Edit: July 28, 2022, 09:45:50 AM by antonis »
"I'm getting older while being taught all the time" Solon the Athenian..
"I don't mind  being taught all the time but I do mind a lot getting old" Antonis the Thessalonian..

duck_arse

Re: Problem with custom overdrive circuit
« Reply #7 on: July 28, 2022, 10:38:49 AM »
nothing but humm is often a symptom of wired-wrong jacks. we can't see what you've built until you post photos, so we can only guess. also, voltages - no supply volts often means no signal thru.
up, higher.

josephfra

Re: Problem with custom overdrive circuit
« Reply #8 on: July 29, 2022, 04:42:15 AM »
Found the problem. I put the input and output jacks on the PCB on the other way to how pedals normally do it. Works absolutely perfectly when you swap the cables over ;-;

Thanks for all the tips/advice with the design too! It's nice to see that if I make it again I can simplify it a bit.