Pedal makes high-pitched squeal when bypassed and power is connected

[Delicieuxz]

I got this pedal recently and it makes a high-pitched squeal whenever it's connected to power and is bypassed. If I engage it, there is no squeal.

I'm probably going to return it, but I though I'd ask what the issue might be. Maybe there will be a guaranteed simple solution.

Here's a video showing the issue:

I've tested it with both 9v power and AC adapter power, and through multiple amps. The issue has been persistent.

[fowl]

Strange.  I guess it's not true bypass.  Can't blame power supply, batteries don't make noise.

JCM800 cab?  I used to have one exactly like that.

[Delicieuxz]

The cab is a JCM 900. It's the same as an 800 cab, though, with the same speakers.


I've tried different amps, cabs, and power sources to isolate the issue to the pedal itself.

[anotherjim]

I can't see without watching the videos what this pedal is. But, high gain distortion/drive circuits can be prone to oscillating when the connections are opened in bypass by the footswitch and this can couple by radiation/capacitance into the input and output connections. This is more likely with true bypass. The solution is a footswitch wiring scheme that ground the circuit input when bypassed. That said, it's hard to see how a commercial product could make it onto the market if that is the trouble.