noisy AC power circuit

I’m visiting a friend in Seattle and brought my equipment with me – ART TPS 2 pre-amp and Echo Indigo IO in laptop. There is a lot of audio noise being generated when both the TPS and teh laptop are plugged into the wall circuit. If I unplug any one of them, the noise disappears. So for now, I’m leaving the TPS plugged in (necessarily) and running the laptop on battery power. Anyone know of a line conditioner/filter that might help?


When you say, “noise” Gary, do you mean hum?

If so, then you’ve probably got a ground loop somewhere.

What that means, is that ideally all grounds should be in a star configuration, i.e., all grounds come together at one common point, which then goes to system ground.

And there should not be more than one ground route from any piece of equipment to that one common ground point

But if you have a ground loop or two in your setup then you’re asking for trouble.

If you do have a ground loop, and there’s no way of rearranged your various power and signal cables, then the one thing to try is “lifting” the grounds of one or more signal cables, i.e. disconnect the ground at one end of the cable, (and that’s one end, not both ends).

You can also lift a ground off a power cable, BUT DON’T DO THAT UNLESS YOU’RE ABSOLUTELY SURE YOU KNOW WHAT YOU’RE DOING.

However, if you’re referring to some other type of noise, could you describe it better?

But even if it is other types of noise, it could still be due to a ground loop, because it can act as an antenna, picking up any stray EMF that’s around, even the local AM station! :D

So anyway, if you do have a ground loop, filtering won’t help, because the problem is what your set-up is causing, not what’s coming out of the wall outlet.

I once worked on installing a studio on a site that had a 5 volt video signal between gound and neutral (it was next door to a TV transmitter), we filtered the mains, but we didn’t have to, it was just a belt and braces thing, but it was easy to tell when one had a gound loop, you could listen to BBC news coming out of the unbalanced foldback microphones! :D


Thanks Ali. That’s probably what it is. It almost sounds like the noise you get on a SW radio between braodcasting stations. There is also some additional crackling and chirping when I move the mouse.

When you say “rearrange various power and signal cables”, I’m not sure what options I have. All the grounding is built-in. What should I be looking for?

From the ART pre-amp to the Echo Indigo IO card, I use a 2 x 1/8" (2 mono) to 1 x 1/4" (1 stereo) cable. I wonder if there is somethng I can buy that “lifts” the ground on this cable (like a different cable :) )


Sorry Gary, I don’t know what products are available in the USA, so can’t help you there.

And it’s very difficult trying to diagnose a problem, or suggest a precise solution without being there.

And to be honest, I’m not even very familiar with American electrical systems.

But just looking at your first description, the fact that unplugging one piece of equipment from the mains supply does cure the problem does indeed suggest a ground problem, either ground loops, or a bad ground on the mains circuit.

So all I can suggest is that you look carefully for ground loops, but without knowing the equipment in question, I’d be reluctant to suggest lifting the ground off the mains supply to one of the pieces of equipment. (Although, if I were there, it’s probably something I’d try, but only after checking the supplies were double insulated, because it does have potential hazards).

Sorry I couldn’t be more helpful.


Thanks Ali. But believe it or not, the noise magically disappeared last night. Everything sounds pretty clean so far. I expect that there must have been something turned on in our guest’s house that was interfering – not sure what.

Ah! Ok! The precise diagnosis now becomes transparently clear!

Fairy Dust!

Either too much, not enough, or the right amount in the wrong place! :laugh:

Anyway, glad to hear the problem is gone, so get your arse in there and make some good music.

It matters. :D



What you describe could be caused by a refrigerator or AC compressor kicking in anywhere in your home’s mains circuits or guest room. The compressors have a big filter capacitor on them to filter out the noise but they can go bad and lead to a lot of line interference. Even when the capacitor is good, compressors are notorious for introducting noise. Another culprit is those infernal light dimmers. The cheaper ones introduce a lot of buzz on your mains.

Another thing you could try is to get a power strip with RFI filtering. I used one in another DAW setup and it cleaned up the mains noise nicely.

There is also a chance that the receptical is miswired. Make sure that the ground wire (typically green) is going to the green ground (earth) screw in the receptical. The white wire should go to the silver-colored screw and the black wire to the brass-colored screw if your home is wired to standard wiring code.

Another handy little gadget is a polarity checker…a little plug-in device with three LEDs on it found at your local hardware or DIY store. I think Wal-Mart has them for about 4 bux. Just plug it into the suspect receptical(s) and the LEDs will indicate if the socket is wired properly. Handy for your gig bag too.