This kit is a clone of the EQD The Depths or more generally a UniVibe.
The pedal works really well for the most part, however, as soon as I lower the rate pot below half and lower the voice pot at all the LFO gradually stops oscillating and I have to max the rate and voice to get it started again. (you can see the build doc here)
I've double and triple checked my component values and they're all good, the only thing I can think it would be is either a dodgy MPSA18 or perhaps my LED isn't quite right?
I've seen this comment which leads me to believe that the circuit is very picky about the LED used. I can certainly replace those two resistors with a trim pot but I'd have to desolder a fair bit to do that so I'd prefer a second opinion before I try that.
FuzzDog Deep Vibes (UniVibe) stops vibing with certain settings
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stolen
- Breadboard Brother
Hi!
To be honest we are not particularly experienced with those simple phase shift oscillators, but we'll give it a shot.
We find it unlikely to be a LED thing. One peculiarity we notice is that C11 has the wrong polarity; flipping it so that the positive side goes to the base of Q1 might resolve the issue. The wrong polarity is in both the kit instructions as well as the original trace they reference, not sure if earthquaker does it the same way? From the structure (3 highpass filters, two adjustable, one constant) this would make sense since the gain at low frequencies could be reduced too much by the detuned constant stage for the transistor to recover - reverse polarized electrolytes often have a significantly lower capacity. It's just a diode drop at bias, but still the most likely option.
If that doesn't fix it: Since you mentioned it is dependent on the "VOICE" potentiometer: Is the point where it stops dependent on the "INT" setting?
All the best!
PS: If you try flipping C11 and happen to have another 1uF cap at hand, you might wanna try that one, it's possible that your currently installed one took some damage. Probably not given the low voltages, but if it's no effort it can't hurt.
To be honest we are not particularly experienced with those simple phase shift oscillators, but we'll give it a shot.
We find it unlikely to be a LED thing. One peculiarity we notice is that C11 has the wrong polarity; flipping it so that the positive side goes to the base of Q1 might resolve the issue. The wrong polarity is in both the kit instructions as well as the original trace they reference, not sure if earthquaker does it the same way? From the structure (3 highpass filters, two adjustable, one constant) this would make sense since the gain at low frequencies could be reduced too much by the detuned constant stage for the transistor to recover - reverse polarized electrolytes often have a significantly lower capacity. It's just a diode drop at bias, but still the most likely option.
If that doesn't fix it: Since you mentioned it is dependent on the "VOICE" potentiometer: Is the point where it stops dependent on the "INT" setting?
All the best!
PS: If you try flipping C11 and happen to have another 1uF cap at hand, you might wanna try that one, it's possible that your currently installed one took some damage. Probably not given the low voltages, but if it's no effort it can't hurt.