Tap Tempo Tremolo

[Guitarmageddon]

Well that's likely going to be your problem.
Dot should be top left, where the "+" sign is.
Carefully desolder it and see where you're at.

[Guybrush]

Still no signal at point 9 I'm afraid. No grounding shorts from 9 through to 13 either. I think it's screwed :/

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[Guitarmageddon]

I'm assuming you flipped the opto?
It might be toast. Do you have another one or an LDR and a LED you can use instead?
One other thing, that trimmer beside the opto is the opamp gain control, you've tried adjusting it?
Also, while the opto is out, try tacking a jumper across 8 and 9 then audio probe to see if signal reaches the output.

[Guybrush]

Yep I flipped the opto and I've adjusted the trimmers but still nothing.

Good news (I think). I snipped the opto out and joined points 8&9 together as you suggy and I got clean signal at both points.

I don't have another opto so I soldered an LED to two of the opto pads (the pair with the + sign) and it lights up and goes out in time with the external rate LED. Unfortunately I'm out of LDRs so will need to get some new ones ordered before I can find out if this will solve it. Do you know what tolerance I'll need?

Cheers!

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[Guitarmageddon]

I'd go with any old thing, they're not especially well calibrated in my experience. Anything that goes 100ohm-1M should cover it. Tayda has them.
When speed and a particular range is necessary designers tend to specify an optocopouler like the VTL in this build, but I've built plenty of good trems with LDR/Led combos.
I've got a few LDRs here, pm me your address and I'm send you a couple of candidates.

[Guybrush]

That's incredibly kind. Thank you.  PM on its way!

[midwayfair]

If you're ever unsure which leg of an optocoupler is the cathode, use your multimeter on the diode setting. The LED will give you a forward voltage only when you have the cathode to the black probe. Or you can stick it on a breadboard and put a resistor and LED in series with it. Flip the vactrol until you get the LED to light up. Then you know which direction the current is flowing.

[Guybrush]

Great tips! Cheers Jon.

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