Ground hum (?) when splitting instrument signal

[bnath]

..:


So, I'm routing a guitar player from one room, into a Little Labs PCP and splitting the outs via the balanced line out and the expansion out to two redeyes into two amps in separate rooms. When just one output is engaged there is no hum, when both are engaged there is MAJOR hum. I tried flipping the grounds on the PCP, the redeyes, and the amps to little avail (one of the amps doesn't have a ground switch though) -- at some point, engaging the earth lift on one of the redeyes changed/reduced the hum level but not significantly.

I even tried plugging both amps into the same outlet via a power conditioner, which didn't help... after which I ran a long extension to connect the PCP as well... so that all three units were connected to the same outlet... not much of an improvement either.

Anyone know what might be going on? I'm not very electrically minded, if that isn't already apparent.

b :*

[Brendan]

It appears that you've accounted for everything except what comes after the little labs box in your chain.

Try taking the AC for your guitar amps from the control room so that everything is on the same AC line.

Different potentials to ground is probably what is causing the hum.

[bnath]

..:



Thanks! I think I tried that -- running the amps, and the PCP from the same outlet -- is that what you're suggesting?

b :*

[Brendan]

Not just the amps and PCP, but everything in the chain, including mixer/premaps/compressor and your computer or tape machine.

This is not how it would be done in a studio that has an ideal ground scheme, but it will get you by.