FV-1 crackles

T

Toastboot

New member
Hello all,
I just build a Arachnid (https://docs.pedalpcb.com/project/Arachnid.pdf) and after a weekend of troubleshooting (with the help of many similar threads here) I almost got it to work. When I power it up it usually works fine for half a minute or so, then the effect changes and noisy cracks appear. I think I might have found (a trace to) the problem, but am not sure how to continue: The internal effects seem to work fine, and measuring the voltages I discovered that at pin 13 (switch between eeprom and internal), the voltage starts between 2.3 and 3.3 after plugging in and then slowly drops until settling somewhere around 0.7 V. The power source is constant at 3.3 .
I already resoldered the chip and am not sure if it or the board survive a desoldering. Do you have any suggestions on where to start (I think I might try and change R5 but am not too optimistic about that)?
Thanks in advance
 
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Maybe start by checking for correct continuity at all pins of the FV-1 as well as around R5 (one side should connect to 3.3v and other to pin 13)?
 
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The most common problem I've had with FV-1 builds has actually been the op-amps, especially when substituting. My experience has been that FV-1 likes working with TL-072 and doesn't like working with NE5532, so if you threw an NE5532 in without thinking that could be something to look at.
 
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When I had a similar issue this past weekend it was a bad cap. Check the voltage at your output Jack. It should be zero. If it isn’t it could be the same issue I had which you can find in my post history.
 
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Thank you all for all the quick responses! I have the TL-074, so that should hopefully be fine - to narrow it down I could simply ignore the fv-1 by connecting its input and output (pin 1 to 28), right? The mixer works and problems only appear in the wet signal. I will definitely check the continuity and voltages again as soon as I have a bit of time and try to find any other anomalies.
 
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What does "slowly drops" mean for the voltage going from 3 to less than 1 volt? Does it correspond to the change in the audio signal getting noise cracks? Odds would seem to be pretty good that they are related.

Does the 3 volt regulatory get warm after it has been running for a couple of minutes and the voltage has dropped to 0.7? Something is either drawing too much juice from that regulator or it might be bad (or both).
 
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