Ground loop

[tedcrop]

A have an interesting issue but you have probably seen it before. All equipment fed from same circuit. All equipment distributed through Furman power conditioners. Each on individual outlets from same circuit. Computers on UPS and fed from same circuit. Recording to DAW mixing in analog.

I have done my best to seperate power from audio. Short cables in racks and very little interaction between power and audio.

Patchbay
24 out from convertors
normaled to 24 ins on console

Mic pres outputs
normaled to convertor inputs

Outboard gear on patchbay and isoltaed
All cables dsub to balanced XLR and TRS

My setup is from left to right:

Rack 1
Apogee convertors
Mic Pres
1176
Masterlink
TT Patchbay

Rack 2
Compressors
Eq's

Console
Soundcraft Ghost 24 LE

Rack 3
Mackie Big Knob- I use this to switch between monitors and inputs.
Motif
KSP8 effects
Two Avalon U5
CD Player

My problem
Console with headphones

1. No cables in console--no hum
2. all 24 ins from patchbay--no hum
3. introduce random outborad gear into indivdual tracks on patch bay--no hum
4. plug mix bus from console into patchbay--hum begins
5. Plug control room out into big knob -- adds hum
6. plug in effects sends and returns -- adds hum

It seems like there is a reason why this is happening. Seems like into the console is golden but out of the console introduces issues. Any ideas? This really sucks because I want to be able to mix down and use bus compression and hear my mix with bus compression--without this hum in there.

[dbbubba]

I don't know the Soundcraft Ghost series that well, but almost certianly sounds like there is a GND issue in the master section of the console.

One thing to look for is a dropped GND reference in the master section.
I have seen consoles produce humm only because the ground plane on a circuitboard was not connected to true ground.
Some less expensive consoles (a Ghost would fall into this catagory) have circuitboards that only get their GND from a screw that is maybe connected to a wire with an eyelet.
Tightening things interanlly can often help these problems.
(as an example: I have four Yamaha 01v consoles and all needed the screws that hold the CPU board tightened because they were loosing their +5V GND reference which those screws provided.)

You might need someone to look at the console.

Can you get a clean output from any outputs like say the 2 mix or XLRs versus 1/4" outlets?
Is it just the monitor section or does the SPKR or MONITOR out have noise too?

I'd try to isolate the problem and look in that area.

Good luck!