Trying to troubleshoot some noise

[Jayco]

Hey gang...

I just finished three days of wiring up on my new pedal board.

I am using a Voodoo Lab Pedal Power 2 Plus to run everything, but needed to make some custom cables to split power to multiple devices.

I was very careful to make sure any time I split the cable, that the ground was lifted on the second end in order to avoid ground loops, but I've got a strange problem.

One of my 'shared' power cables is running my Boss TU-12H tuner and my ProCo Rat...  I select the tuner versus the amp with an A/B switch built from the schematics on the Fulltone website.

Here's my problem... when the amp rig is selected, everything seems fine, but when the tuner rig is selected, I'm getting some bleed through the amp line... sounds like a VERY quiet version of what I'm playing with a distortion pedal turned on (IE - I can hear the audio, but its all distorted).

If I walk down my rig (pedal by pedal), everything is fine EXCEPT for the Rat... when its in the pedal progression, the bleeding from the tuner occurs.

The two share an electrical connection, but not a ground... the TU-12H has the ground lifted on its power cable, so it should be getting ground from the audio line.

Any ideas as to where the noise is coming from and how I can correct it? 

The whole idea behind the A/B box was to not have to change my pedal settings or kill my volume to do a quick tune (the Fulltone pedal shorts the unused channel to ground so that it won't make noise).

I'd appreciate an insight you guys might have.

Thanks,
Jim

[LyleCaldwell]

If you mean you only hear the faint but distorted signal when the Rat is on, I would suggest you have crosstalk in the A/B box that the Rat is (dutifully) amplifying and distorting.

If that's the case, redo the A/B using shielded wire or at least change the wire dressing inside the A/B so the wires to the A and B output aren't running parallel.  Even slight distance can eliminate crosstalk.

[Jayco]

Lyle,

Thanks for the response....

No, the Rat doesn't even have to be on...  you can hear some faint signal, but it SOUNDS like its distorted through a cheap distortion box... even if no pedals are turned on.

The A/B switch doesn't seem to be the cause, as I tried replacing the one I made with a store bought A/B... same exact problem.

I know that you are supposed to have thing powered by the same supply in the same audio path for grounding reasons, and technically these are on two separate audio paths... except for they do share the audio ground, which is always connected to both A and B sides of the A/B box.

Jim

[LyleCaldwell]

Stick a battery in the tuner or in the Rat (with the power cable disconnected obviously) and see if the problem goes away.

[Jayco]

Lyle,

With a battery in the tuner, it is perfectly silent.

Any suggestions for fixing this with the power supply?

As I mentioned, I've got the ground lifted on the tuner power plug as to not cause ground loops with the audio ground, but for some reason there still seems to be a loop somewhere.

Thanks,
Jim