Distortion whistling while bypassed in a looper

[greigoroth]

The short problem description: My distortions are whistling while bypassed by a looper (the distortions are themselves not bypassed) and I can't figure this out.

My setup: I'm currently using three loop pedals - 1 built by Frequency Central - called the "loop guru", and 2 built by me based on GGG's layout,
The loop guru is constructed thus: master in/out, 4 loops, 2 of which are A/B, and two that are simply in series - i.e. can be turned on or off in conjunction with either the A loop (clean) or the B loop (distortion). 3 switches, 4 loops. One of my loopers is 2 loops, A/B - I use this as dist 1 or dist 2 - for the sake of the argument it can be called the distortion looper. The other is just a single loop on/bypassed. I use this going between the guitar and the master in on the loop guru (i.e. pre all the loops in the loop guru). Again for the sake of the argument it can be called the pre-looper.

The long problem description: With the clean loop selected on the loop guru, it shouldn't matter what I have going on in the distortion loop, as it is bypassed. In the distortion loop on the loop guru is, as mentioned above, a second looper, the "distortion looper". One loop has a high gain pedal, the other has a couple of low gain. When the high gain pedal loop is active I get a high pitched whistling sound through the clean loop on the loop guru. The sound gets more intense, up to a point, with more gain or volume. I can change the pitch of it by adjusting the mid frequency on the distortion pedal.

• I have tried 3 different high gain pedals with the same result (although slightly different pitches and tones to the whistling). I have put the high gain pedal in both of the loops on the "distortion looper" and it is still present. The whistling disappears if I select the low gain loop on the distortion looper, or if I bypass the high gain pedal while it is in the high gain loop. However, having to bypass the pedal, when the whole distortion loop should be bypassed anyway, defeats the purpose of having it. So it is not a problem with the distortion pedal.
• I have tried replacing the dual looper with a single looper and just putting a high gain pedal in it. As long as the loop is activated I still get the whistling noise. So it's not a problem with the looper.
• I run all my pedals with a power supply (Cioks Big John). I thought maybe it is some weird thing with the power supply, so I ran the high gain distortion from a Boss PSA. Still whistled on the clean channel of the loop guru. So it's not the power supply.
• Thought that it might have been pre-loop - so I simply unplugged that and plugged the guitar directly into the master in on the Loop guru. Still whistled.
• The weirdest thing of all? The noise disappeared if I activated the "pre-looper". When it was in bypass mode the whistling still occured. But if I activated it the whistling disappeared. It didn't matter if I had any pedals actually in the loop - I could take a single patch cable from the send to the return - but if it was activated the whistling on the clean channel of the loop guru disappeared.
  

What is going on here? Given that the distortion loop isn't even active I shouldn't be hearing anything. But even stranger to me is the fact that turning on another apparently indpendent loop solves the problem. What should I look for to debug it? 

Here's a visual of my setup courtesy of microsoft paint

[petemoore]

  I don't know if the PS's are floating/reg'd, but batteries make excellent floating supply to test PS's against.
  Another thing I'd try first is to ground the circuit input of 1rst Disto with a clip-wire-clip while it is oscillating in bypass. If that works then rewire the switch with DPDT grounded input wiring diagram.

[darron]

i reckon petemoore's on the money. probably not a PSU issue, but a battery will test that.


just because something true bypass and disconnects your distortion doesn't mean that it can't let sound through. distortions and high gain pedals can oscillate if there's there's no signal or something loading the input and that noise can come through your true bypass box by capacitance because it's probably a high enough frequency.

put your looper in bypass and try to short the distortion input to ground, see if the noise goes away. then if it does like pete said rewire the switch to earth the "send" while bypassed - always a good practice anyway (:


this i suppose is especially the case for our booteek pedals without buffered bypasses...

[greigoroth]

Thanks for the ideas dudes .

I'm pretty sure the PS is fine, the Cioks stuff is well made and I've never had probs with it before. Also tried it with a bunch of commercial pedals, both TB and buffered, same thing happens. Strange! Rick's got in touch so I'll hit him up with some more ideas - he knows a hell of a lot more than me and builds awesomely so I'll put my faith in the Freqster!