Gas Tank Leak

[davio]

Recently built a Gas Tank and Junk Trunk and they're awesome. Minor problem with the GT that's more of an annoyance for my OCD: When I turn both the clean and fuzz volumes all the way down there a trickle of fuzz coming through quietly. Any idea where this bleed could be coming from?

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[davio]

To clarify: Not just background static. I mean that if I turn down both levels, there is a faint signal of my playing+fuzz still going through. It sounds somehow distinct from the signal going through the fuzz side of the actual circuit.

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[jimilee]

Sounds like a solder bridge. Have you checked that, taken voltages and reflowed all your solder joints?


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[EBK]

I think it's just the design.  Try throwing a cap in that C8 spot that Brian says to omit.    It would reduce the AC impedance for the VB node, which may reduce bleedthrough.

[davio]

Sounds like a solder bridge. Have you checked that, taken voltages and reflowed all your solder joints?

That's what I thought at first. I went through an reflowed everything and checked everything I can think to check but all seems to be as it should with this one odd exception.

I think it's just the design.  Try throwing a cap in that C8 spot that Brian says to omit.    It would reduce the AC impedance for the VB node, which may reduce bleedthrough.

I'm afraid you may be right. I tried throwing a cap in there but there was no discernable difference. :/

There are zero real world scenarios in which I'd hear this since both clean and fuzz volumes would need to be turned almost completely off with the pedal switched on so it's not a big deal in any way. I was just hoping it was a simple fix of a simple thing I screwed up somewhere along the line.

Thanks for the help and let me know if anything else happens to occur to you that I can check!

[madbean]

I agree that this is probably an unintended consequence of the design. The lack of dc coupling caps and tying the volume pot to virtual ground instead of signal ground may be why you still have a little bit present when it should be "off". Maybe DC offset from the op-amp itself contributes to it? I suppose you could try alternative quad amps to see if it eliminates the issue.