Ground Loops

[Chewie]

I was content to say "that's noise." But now I really want to know what it really is, what causes it and how to avoid it.

 

[Farview]

It happens when you hook two (or more) pieces of equipment together and one is grounded better than the others. Electricity takes the path of least resistance, if that path is across the audio lines and through the other unit, it hums.
The way to avoid it is to make sure everything is equally grounded.

 

[Chewie]

How you make it equally grounded?

Other than the lack of noise how would I know if the components are equally grounded?
Is there a way to test?
If I have to use the equipment exactly as is with this noise what could I do the reduce the noise without altering my setup?
When you say grounded what does that mean? Is it inherant in the device or the wiring it is connected to?
Does grounded refer to the ground wire or the neutral wire?

Also how would one differentiate between noise caused by a ground loop and other noise?

 

[Farview]

Grounding relates to the ground wire (the 3rd prong on the wall outlet). If you plug everything into the same power strip, you should not have a problem. The problem normally happens when you have some of the equipment plugged into a different circuit than the rest of the stuff.
A ground loop is 60 cycle hum, you can find out what is causing it by unplugging things one at a time until the hum stops.

 

[Chewie]

I'm assuming changing around the plugs is what will fix this but other than that is there anything that can be done?

 

[Farview]

If it is happening due to equipment that isn't grounded because it uses a wall wart, it may be looping through the rack rails. There are isolators called humfrees that you can get to isolate these things.
A similar noise can come from having something that is not well shielded too close to something with a big transformer. You really have to figure out what piece is introducing the hum into the system before you start trying to fix it.

 

[Chewie]

Ok well for example my speakers make noise when my UPS is on. Whether or not the computer is on. What about that?

 

[mshilarious]

Ok well for example my speakers make noise when my UPS is on. Whether or not the computer is on. What about that?

A similar noise can come from having something that is not well shielded too close to something with a big transformer.

Speaker wires usually aren't shielded, but the hum is quiet enough that most people ignore it. My speakers have a tiny hum, but I can't hear it 1 foot away from the cone.

If it's a loud hum, you could use shielded cable (might be tough to get in the proper gauge), or you could try shielding the UPS. My UPS has a metal case, my power amp sits right on top of it, and is plugged into the UPS. There is no hum from the UPS in the speakers.

Do be sure to check that it's not hum from problem #1 Farview listed. Plug in your power amp & the UPS into the same outlet, turn everything else off, and see if the hum goes away.

 

[NYMorningstar]

You might also avoid crossing your speaker wires over any power cords and if you can't, try crossing them at right angles to minimize the interference.

 

[Farview]

If they are speaker wires, do what has been suggested. If you have powered monitors, they are not really speaker cables. They feed line level signal to the amps in the speakers and will pick up interference very easily. Keep these cords away from power cords, transformers, ups's, radio trasmitters, microwaves, television sets, CRT computer monitors, the power supply to the computer, etc....

 

[Chewie]

Wow!

Now that's a lot of info but looking at my setup i'm sure those suggestions will work. I didn't realise so many things would contribute.
But noise caused but wire not shielded etc isn't called a ground loop, right? So wht is it called?

 

[Farview]

It's called 'noise caused by unshielded cables'. Or interference.