Possible ground loop problem, going crazy here guys...

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Member Since: Jun 27, 2004

Hey all! Got a bit of a problem here and I'm hoping someone can help, cos I'm about to go insane! Okay, below is a link to a very crude diagram of my system!


As you can see, the POD XT Pro is connected to my M-Audio FW410 in two ways; by SPDIF, and by a single unbalanced 1/4". The purpose of this is so that I can record the dry, and effected guitar simultaneously, then feed the dry guitar back into the POD over SPDIF to change the amp tone at a later date! Sounds great.

Only, when I do this...I get noise. And it corresponds with whatever is going on on my laptop. If I move the mouse, or open a window, I can hear it. If I just run the XT Pro straight into my soundcard, there's no problem, but its as soon as I try and go back into it that the problem occurrs.

Thing is...when I unplug my laptop...the problem dissapears. I've also tried removing my amp from the equation, makes no difference. Only unplugging the laptop from the mains helps. Also, if I move the plug tree ever so slightly, the noise *almost* dissapears, but it comes back eventually.

Any help would be greatly appreciated! I'm *almost* convinced that I need to lift the ground on the laptop power supply, but I read somewhere else that sometimes, these things seem like ground loop problems, but are actually the result of "switching" power supplies, in which case, lifting the ground would solve nothing! And I'm also very confused as to what kind of connection allows a ground loop to form.

Thanks very much in advance,

- Paul

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Since: Jun 27, 2004

Aug 18, 2005 03:22 pm

Sorry to double post, but just a thought;

If I'm only getting the hum/whining when I use the unbalanced audio connector, then does that mean that is what's acting as the ground path? And can I just whack (see: buy) a DI box at this point and isolate this path?

Since: Apr 03, 2002

Aug 18, 2005 03:26 pm

Weird issue, I would suggest maybe trying a power conditioner on the laptop, or something to make sure it's clean power...perhaps the power cord is going bad...I dunno, I'm just kinda spewing ideas as they come to me...make sure none of your signal cables get anywhere near the laptop power cord...

...bringing sexy back
Since: Jul 01, 2002

Aug 18, 2005 06:24 pm

my laptop does this same thing, albeit with different gear. on batteries it works fine...

power adapters are dirty noisey things indeed.

Since: Jun 27, 2004

Aug 18, 2005 06:38 pm

Hmm. This is really puzzling. See when I run the POD, into the 410 by SPDIF...there is no noise. Where the problem is occurring is through the unbalanced 1/4" that's going from "Dry Guitar Out" on the POD, to the line input of the 410. So I tried placing a passive DI box inbetween these two points, and using the XLR inputs of the 410 instead. Unless I was doing it wrong somehow, it didn't work :( Worse still, when I took the power off the laptop, the signal was still extremely noisy. When I touched the FW410, the tone of it changed slightly.

Really stumped. I don't think I'll go hacking plugs up just yet. There's gotta be a way around this. I mean it's not a show stopper...but it does mean that if I do the perfect lead take, and decide I'd like it through a 4x10 tweed, with more wet mix on the chorus...I have to play it in again as opposed to "re-amp", which was the big selling point of the XT Pro :(

String bender
Since: Unknown

Aug 18, 2005 07:16 pm

First thing I would suggest is make sure none of your guitar cables are lying on or under your laptops power cord. That happened to me not too long ago and for me the answer was just to seperate the cables.

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