I just received my M-Audio BX5s, and have them plugged into my Nuforce icon 2 DAC which is connected to my computer via USB ( Speakers <- Dac <- Computer ).
The problem i am noticing is, if i turn the volume on the back of the speakers up more than half way, i can hear this high pitch hum after playing music for about 40 seconds then it stops. 

I did a few tests and plugged the speakers into my phone, and i did not get this high pitch noise, i have balanced cables as well. 

Sounds like a ground loop. Try plugging the speakers into the AC power using 3 prong->2 prong adapters.

billybob_jcv said:

Sounds like a ground loop. Try plugging the speakers into the AC power using 3 prong->2 prong adapters.

Click to expand...

So my 3pin power plug from my speakers i want to convert to a two pin plug?

Here's to summaries my situation

Observation 1. 
The high pitch noise is only temporary, when playing any type of audio (even if my volume is turned off). Then the high pitch humming will turn off after a few seconds.

Observation 2.
I only seem to get this temporary humming when i use the USB input into my DAC. i have tried 2 other USB cables and 3 different ports on my computer. 

Observation 3.
When plugging the AUX from my phone into the DAC there is no humming noise. 

Observation 4. 
When plugging the AUX from my computer into the DAC there is a very loud humming/static noise (worse)
    - same when bypassing the DAC (COMPUTER -> SPEAKER AUX)

Observation 5.
When plugging the AUX from my Phone into the speakers, there is no humming noise. (bypassing the DAC) 

Observation 6.
I can stop the humming noise instantly if i remove the USB from the DAC. 
     - The humming does not stop if i turn the volume on the DAC all the way off.

Prediction 1.
I read into ground loops, and followed all steps on how to fix. I have a feeling it isn't Ground Looping that is effecting my system as the humming is only temporary. 

Prediction 2.
It isn't the DAC that is causing the problem (observation 3) 

 

The USB Cable Shielding is also grounded to PC= double ground =causing (datastream) groundloop noises!
Solution= Cut at only 1 side the USB Shielding wire/mess of the USB Cable.

http://www.theworshipguitarist.com/blog/theworshipguitarist-experience/usb-ground-loop-noise-eliminated/

m0jo
View December 12, 2010

I tried this, at first the usb device (a Digitech GSP1101) wasn’t recognised and didn’t see the USB connection.

It turns out that you have to leave the black wire connected!
For me the hum wen’t away with just the outer shielding cut away and the black wire still there..

This could have something to do with the fact that at the ports, the pins are connected to the circuit board, and the shield is connected to the casing.
Ultimately the board and case lead to the same ground, but apparently not perfectly..

So, try it with just the shielding cut first, you can always still cut the black wire if it doesn’t work.

Click to expand...

http://www.head-fi.org/t/744375/burson-conductor-sl-9018-volume-bleed-with-low-impedance-headphones#post_11088122

Now your mS USB [ground]-PC connection is causing the Ground Loop noise! because the audio ground is also connected to PC.
Double grounds to PC makes the groundloop statics noise!

Just test it without USB conneected, you will get clean sound from mS line-out to PC soundcard line-in directly!

-Simple solution fix: just cut the USB cable ground pin 4.
-I bought a cheap 4 ports USB hub from ebay and cut inside the ground trace/shield to the usb output port(s).
Remember now mS USB will be only active when the audio line is connected to PC also, because USB ground will now using the only one audio ground.
I get the same clean sound likewise as without USB connected, just perfect sounds!

Ref:
http://www.archonmagnus.com/computing/elec/USBpins.php

http://www.moddiy.com/pages/USB-2.0-%7B47%7D-3.0-Connectors-%26-Pinouts.html

http://www.head-fi.org/t/686609/usb-cable-cutting-ground-black-wire-to-eliminate-noise-between-computer-and-dac-solved

http://www.theworshipguitarist.com/blog/theworshipguitarist-experience/usb-ground-loop-noise-eliminated/

Click to expand...

http://www.korgforums.com/forum/phpBB2/viewtopic.php?t=92032

Hi there, thanks for the help, but it has not solved the problem. I just did as you said, cut out the grounding section of the USB. The signal comes through perfect, but when i pause the song the hum/whine is still there. then after 30 seconds or so, itll disappear and the speakers will be silent. Still the same problem. 

Is the noise still the same there when only the headphone is connected to the DAC with/without USB connected to PC???

If the same noise happen only when DAC USB cable to PC is connected is still USB shielding wire/mess is connected.
Do you have a multimeter to test the shielding/wire connections?

Like the guy above said, if the speakers powersupply have groundwire (3pin) to the mains as the PC= power earth groundloop, than you'll need to lift the speaker power earthwire or to 2 pin converter.

I dont have any decent headphones to test this out with, and i dont have a multimeter, Iv just settled to turn my speaker volumes to 50% because i can barely hear the high pitch hum, and ill just adjust the volume from the DAC, which doesn't affect the volume of the High pitched hum

What happened if you connect to the speakers from the PC Builtin Soundcard output only?

Since the PC, DAC and speakers using their own powersupply the problem is still their earth groundloops.

cdsa35000 said:

What happened if you connect to the speakers from the PC Builtin Soundcard output only?

Since the PC, DAC and speakers using their own powersupply the problem is still their earth groundloops.

Click to expand...

Very bad humming/hissing, 

Ok thats confirms the PC audioground to Speakers with PC powersupply earthwire to Speakers powersupply eartwire = 2 grounds =groundloop.
Thus lift the Speakers powersupply earth to 2 pins will minimise the noise!

http://www.epanorama.net/documents/groundloop/basics.html


Other solution:
http://www.channld.com/hum.html

lol - which is what I suggested in post #2...

So whats causing this is defiantly ground noise? i was wondering if i could take the ground section off my 1.4" cables, would that fix my problem? i looked at the other fixes you have posted, and also did some reading but not sure i want to unsolderer my new cables to test it

Have you tried using this on the BX5s?
http://www.homedepot.com/p/Leviton-15-Amp-Gray-Polarized-Grounding-Adapter-R55-00274-0GY/100356839

Hi there, ill have to head into the electrical store tomorrow, but to give you an update. I snipped the grounding part of the USB, and it cut the low HUM out that persisted at high volumes, but the 30seconds high pitch hum is still there after i play audio.

I tried, un soldering the Grounding section of my 1/4" cables. Which did nothing. (all hums still persisted) so i re soldered it.

i have high hopes for the grounding adapter you linked.