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Computer Grounding Loop problem

post #1 of 4
Thread Starter 

Hello all. I'm having a problem with distortion in my audio, as fellow hi-fiers, I'm asking for your help please!

Current Home Rig: Balanced> Sennheiser HD650 > Little Dot MKVII+> Matrix Mini-I Dac via USB


Through my balanced amp, there is no noise. However, when I use the 1/4th single end from the amp there is a lot of static/floor/humm noise. I've determined that it's not the Matrix mini-i DAC (which is connected via USB, I also tried using a different DAC and its even worse) The only way I can hook my DAC up to my PC is via USB. (I don't have optical out, which is the only other way to get bitperfect). My computer, amp, and DAC are all plugged into the same power strip. My computer components are


1) Cheap emachines mobo (That has ONLY one PCI-E slot which is being used by my graphics card)

2) 400 Watt continuous Antec Earthwatts power supply

3) Core2duo 2.86ghz processor

4) Geforce GTX260 Maxcore

5) 4GB DDR2 Crucial

6) 1TB Hitachi HD


I have plugged my amp directly into the power supply without having any input from any source, and I did notice some distortion although it took awhile to build up. I tried using a 3 to 2 prong adapter for the power and that did reduce the noise (nearly inaudible at +110db with 38ohm M50's). So I think I have a grounding loop problem.


The solutions that I've thought of and read from other people's posts are


1) Get a galvanic isolation USB dongle. (I'd like one for USB 3.0 if possible) This is the only one I found http://electronicsshop.dk/galvanic_isolator.htm?currency=EUR  WITH a cheap Isolation transformer power supply dedicated for the amp/dac.

2) Get a PCI sound card with optical out with cheap isolation transformer for amp/dac

3) Get a new mobo that can ground w/ cheap isolation transformer for amp/dac

4) Get a more expensive isolation transformer power supply that will power my computer, amp/dac

5) A line reconditioner if there's a really good one that's highly recommended for use with amp


I'm looking for


1) Cheap alternatives

2) Good options/products for any of the above mentioned options

3) A $250< Solution


I just dropped 1.2k on audio equipment for my setup, so buying a brand new computer isn't an option for me right now. Any other options, suggestions, comments would be helpful! Thanks!

Edited by Kost - 10/2/12 at 10:34am
post #2 of 4

Some friends have used external powered usb hubs and the problem disappeared (they are cheap, you can try). It could be a noisy PSU problem also. 

post #3 of 4

Your computer requires an earthed mains supply as well as the little dot and therein lies the problem. The amp and PC are at different earth potentials as far as noise is concerned.


The USB cable provides the path for the noise from the PC to travel through to the Little dot, via the DAC which is not likely an isolated design, don't worry many DACs that are $000's aren't either.


I would attach a ground wire say 10g (4mm) flex or 5mm to 10mm size braid from the computer case to the little dot case fixing screw (with the paint removed) at the rear. The idea is that the PC and the Little dot will have the same earth potential, since the heavier wire hopefully will attract the noise to that part of the circuit, (due to a lower impedance) rather than an arduous path through USB-Dac-Amp-Phones. 

If that's successful, the best method is then to drill a permanent hole on the metal case of the Little Dot to attach a wire permanently, since a fixing screw is designed to be that, for fixing and not for earthing.

post #4 of 4
Thread Starter 

Thanks, ill give it a try

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