Vibrato build log

[cloudscapes]

Problems with bypass popping that isn't on the breadboard prototype. For some reason, my opamp's inputs are outputting voltage. But it was passing clean sound, so it's not "fried". It's just that it unbalanced the levels everywhere so that the final output was 300mv higher than it should be, causing a pop (even with pulldowns).

It's not other parts of the circuit, since I've been cutting traces to isolate where the extra voltage is coming from. My opamp is literally outputting voltage from the inputs, even when they're cut. I've really had it up to here with electronics. These problems are "magical", they don't have roots in logic, and my brain can't handle that. I work best when things make sense and have a reason for happening. This does not.

Logically, I'd remove the offending opamp and put in a new one, but at this point my board is such a mess with the fixes and bodges that I can't trust this board anymore. I have to make a new clean one, and even then I'll not have figured out where the problems are coming from in the first place.

[Kipper4]

I hope you work it out Etienne. It can be infuriating when things go wrong and you think of all the hours you put in behind the scenes.
Keep going fella you'll work it out. I can't help much beyond encouragement this stuff is a long way beyond my pay grade. Someone much smarter than I will surely offer more practical help soon.
Bows to Cloudscapes in appreciation of sharing your knowledge.
Thanks.

[anotherjim]

I hope you work it out too.
We don't have sight of your circuits, but assuming they aren't faulty, op-amps are computers -  garbage in = garbage out. Just  remember that the connections around the amp are the computer program, so there must be something wrong with it. It isn't magic - something is causing it.
Remember the dirty flux trouble you had with the FV-1 clock? Could be as simple as that.

[cloudscapes]

The flux trouble with the FV-1 wasn't simple, though. I square that away right on the illogical shelf as well, considering my past experience with the same flux used on theoretically more sensitive (higher speed) components. It was an exception, and it took too much trial and error to solve. I don't want these kinds of issues to keep happening. They burn me out in the long run.

Back to this one. I don't see what else it is other than the opamp. But I admit I can be wrong. But if I'm wrong, I don't have anything else to go on, so I'm a bit stuck. With the traces I cut to test and measure voltages, I had a vref of 4.5v (common 10k voltage divider), feeding into the + of the opamp. The - was left floating, and the output was measuring 6.8. The flux was cleaned off (I learned my lesson). I don't see how that can happen unless the opamp was defective. Maybe someone can say otherwise, I may be wrong. It still passed sound, though, except it was offset from vref, which caused the pop.

With nothing else connected, because of cut traces. With 4.5v vref (measured before connection) to the +. No flux either. All go to 0 when no vref connected.


I'll do a fresh board, once I have the parts. Can't do much else. If I still get erratic voltages on the inputs/outputs, whether opamps or something else with the analog section, I think I'll just redesign the analog mixing/buffering.

[anotherjim]

As per your sketch, it looks like the op-amp is feeding from it's +9 out to the +input, over-riding Vref, that does look like a chip fault.
As per your text, with no connection to -in, it will drift via leakage (very high impedance there). Measured output could be true for a working amp in that condition. A temporary blob of solder between -in and out pins should give +in voltage at output if amp is working.
Assuming the amp may be good...
I'd look for some path to ground where the -in is fed from. That would cause the amp output to rise above Vref. If you have any tanatalum caps in that path, they could cause it. I've had experience of that. The only place I'd use tant' now is on fast logic power rail decoupling.