Troubleshooting Ground Loop

[rsadasiv]

I had to disassemble and reassemble my computer recording setup, and I have been plagued with a 60 cycle/ground loop hum ever since. I have tried unplugging one by one every peripheral attached to the computer (~15 devices) and I still have the hum. Any suggestions for getting rid of this? It's driving me crazy.

[Electriclight]

Are these peripherals like a rack setup or what? I've only got the same ol advice you already know. Everything should be coming from a common receptacle. Are there any two prong non-polarized plugs in the mix? Did you rearrange the physical layout of the gear---put anything near the monitor? CRT monitor? I'll think about it some more. Good luck.

[brandondrury]

Interesting. There is nothing within the computer that should cause this hum that I can think of. I'm not sure what changed for you here, but just for the time being, I'd recommend ruling the computer out of the equation. I'm thinking more along the lines of cables running over power cords and things of that sort.

What audio interface do you use? Does it have a breakout box?

Brandon

[rsadasiv]

Originally Posted by brandondrury

Interesting. There is nothing within the computer that should cause this hum that I can think of. I'm not sure what changed for you here, but just for the time being, I'd recommend ruling the computer out of the equation. I'm thinking more along the lines of cables running over power cords and things of that sort.

What would be an example of cables running over power cords? Physically on top of each other (like the shielding on some of the cables is not up to spec)?

What audio interface do you use? Does it have a breakout box?

Delta PCI Card -> Delta 44 breakout box -> trs cables -> behringer truth powered monitors.

It's not rack equipment, everything sort of sits together on a converted dining room table. It's a complete rats nest of cables under the table. There is some CRT noise and some fan noise, but the hum in the monitors is much much louder (in addition to being optimally directed right at my head). There are three power strips and six possible wall sockets with several two prong connections along with three prong and wart plugs. The power is untreated, but I am pretty sure all six wall sockets are on the same circuit (all on the same circuit breaker).

I have tried changing the trs cables and replacing them with mono instrument cables - no change. If I disconnect one of the trs cables the hum goes down. If I disconnect both of the trs cables the hum goes away. If I turn up the gain on the monitors the hum gets louder. If I turn up the gain on the breakout box the hum does not get louder. If I plug my (stereo) headphones into the breakout box I don't hear any hum. Changing the outlet/power strip of the speaker power does not affect the hum.

I don't really understand what a ground lift does, but I am seriously considering buying these 1/8" stereo hum reducers from Radio Shack and putting on 1/8 - 1/4 converters to get them into the monitors.

[rsadasiv]

On further review, it is the Delta 44. If I plug in to my POD the hum is gone. Kind of sad, because the 44 is the oldest piece of gear I still use and it has worked well over the years. On the other hand, I am ecstatic to be sitting here without the hum.

[brandondrury]

What would be an example of cables running over power cords? Physically on top of each other (like the shielding on some of the cables is not up to spec)?

Cables that pass signal (and not power) such as 1/4" guitar cables or XLR cables can pick up noise especially from wall warts. I've done this before, but I have to admit that I can't remember the last time it happened.

If I turn up the gain on the monitors the hum gets louder. If I turn up the gain on the breakout box the hum does not get louder.

This is a crucial clue here.

What happens if you disconnect the TRS cables from the Delta44 but leave them plugged in your monitors?

Brandon