Promethium HM-2 Issue

saucy_boss

saucy_boss

New member
Bypass works, effect works, but there is a high pitch squeal when volume and/or gain are past noon. Nothing is grounding out in the case, as I made two identical pedals and they are having the same issue (one is for a friend), and it is out of the case. Here is a guts shot and a video

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Q1 (2N5457) is out of production and feels a bit suspicious. Where did you get yours from? If it's a fake that could be where your problem is coming from.
 
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They're probably ok then. Do you have any spare TL072's you can try? I don't think they're the problem but they're socketed so worth checking.

Squeeling sounds more like it could be a bad cap somewhere. Double check all your component values, especially around the volume and gain pots. Do you have an audio probe you can use to check the circuit?
 
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Since you have 2 identical circuits having the same issue, either you made the same mistake twice or it is an external factor causing the issue. Rule out the external factors first. which are guitar, cables and power supply. If you have alligator clips, connect battery to DC jack inside enclosure. Be careful, easy to short battery doing this. Try different cable and guitar. If you still have a whine then you will need to use an audio probe to find out where it starts in circuit. My guess is that the whine is always present, it just becomes noticeable when amplified by turning up the gain/level.
 
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