Horrible hum coming from bypass looper - help!

Well, after lots of time and money, I finally have my big pedalboard set up for stereo. Yay! Sounds amazing, except for one thing.

I have an American Loopers bypass looper, a pretty big one, has 6 mono loops and 4 stereo. Now, for a reason I can't figure out, whatever pedal is on loop 10 (the last loop), there's a constant and obnoxious hum. I sent it back to American Loopers, he couldn't reproduce the problem, even sent me a video showing how he couldn't reproduce it. He tried it in stereo, as well as mono, as well as each side. I've tried to troubleshoot, here's what I've done, all of which made no difference.

• Put other pedals in that slot
• Doesn't seem to matter if other loops are engaged, or not
• Tried it just mono
• Tried another new cable
• Put the pedal on it in another slot (didn't make noise on that slot, so it's obv. not the pedal).
• Powered it from one iso power supply.
• Powered it from another iso power supply
• Powered it with its own power, just plugged in
• The looper goes back to an Empress stereo buffer, to a DI, then XLR's out to my PA. Tried the ground lift on the DI.

I'm kind of at my wit's end, here. The looper is so quiet, except for that last loop, and I need that last loop, too. What could this possibly be? Out of options, here. Also gonna post this in the repairs section, hope that's okay.

 

The only thing I haven't tried is plugging it in to an outlet that I know it is on a different circuit. Just spent another hour trying different things. Baffled.

 

Actually, after I posted, I went and unplugged everything except loop 10, still had the noise. Thing is, the cables are pretty new, but I'm gonna try some other ones, tonight. Thanks.

 

You know, I didn't want to go there, but there is something in the back of my mind that has me wondering about that side of the equation.

What is a 'charge pump'? I've tried it with different pedals in that slot.

 

I don't know what frequency, but it's that typical hum you get when you have a bad cable or something. I haven't tried bypassing the bypass, but I will try that tonight. Thanks.

 

Thanks for the explanation. The pedals are Meris pedals, perhaps, just for the heck of it, I should try a different one, like my H9 in that slot.
I've been looking around on the internet, I don't really have a lot of other options, as far as this many stereo loops, the RJM is the only one, and I can't drop over 800 on a bypass looper, now. If I can't fix this, I'll just have to double up two pedals on loop 9. I did buy this used.

 

Will do, thanks.
Could the proximity of the power supply to the bypass looper have anything to do with it?

 

I don't know if it's purely passive, it does have preset and midi capability, which I don't use. The thing does have a big circuit board in it. But I'll try that, too.