SOLVED Abyss bizarre LFO/LED behavior

jpd

jpd

New member
Hi all,

I’ve built 4 Abyss pedals in the past with no issues, but having a weird issue on my latest build that I can’t figure out.

When power is first applied, the LED blinks at rate as intended, but eventually after about a minute, it doesn’t go all the way dark, then eventually the LED just stays fully lit. I get phasing as expected, then I still get the boost from the level knob, but no phasing as the LED stays on. I’m assuming this has something to do with the LFO part of the circuit.

Ideas for things to look at? I pulled it from the enclosure to make sure something wasn’t shorting or grounding out, still does it out of the box. Wondering if anyone has test voltages on the TL074 pins I could check against. I tried swapping another TL074 with no joy.
Thanks!
 
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you might have a capacitor in the LFO circuit installed the wrong way. it may be charging during the LFO cycles and discharging enough to light the LED when it should be going dark. when you turn of the power the capacitor discharges and resets.
 
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zgrav said:
you might have a capacitor in the LFO circuit installed the wrong way. it may be charging during the LFO cycles and discharging enough to light the LED when it should be going dark. when you turn of the power the capacitor discharges and resets.
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All of the caps were the right values and in the right direction, however, I used thinner adhesive squares for the backs of the rate and throb pots, and the rate pot is right above C14 and 15. Going to desolder and try a thicker barrier, I’m assuming I’m shorting out against the back of the pot somehow.
 
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Annnnnnd that’s the ballgame. One of the wraparound tabs in the back of the dual-gang pot must have been making contact on C14. Thanks zgrav!
 
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