Aion Quadratron (Lovetone Doppelganger) LFO Issue

[benny_profane]

My quadratron build has a slight issue with the LFOs when dual mode is activated. In single LFO mode, the entire range of knob is useful. In dual LFO mode, the upper third or so locks up the LED at full brightness with no oscillation. Note that at least one other builder has had this issue.

The build has the suggested LEDs (Tayda diffused green). The span pots have been increased to B2K from the original B1K. I've tried tacking a 2k resistor in parallel with the pots to simulate the stock value, although I don't think that this is related to this problem. The problem is exhibited when the pot is completely turned up and there is no resistance between the output of the op amp and the series resistor / LED array.

I've tried swapping the IC6 with another TL022 with no change in behavior.

I pulled one of the LEDs for testing. I'm getting consistent Fv measurements with two different meters for that LED and samples from two different batches of green diffuse LEDs from Tayda.

I'm stuck (much like the LEDs).

BUILD DOCUMENT

 

[scott3t]

Mine is working but only the 2 outer green LDR/LEDs are strobing. I have voltage at the LEDS and the LEDS test as working

 

[spartan1017]

To add to this, I've also built the Quadratron with both the recommended Mouser (BOM) and Tayda (build doc) LEDs tested.

With both configurations, I'm experiencing the lock up in dual LFO mode. It only seems to happen at the higher 1/3 of the span pot range. All parts are as per the bill of materials. It's an excellent device and I don't think this issue really affects it's usage, but I'd love to know how to solve it all the same