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Usb Cable, cutting Ground (black wire) to eliminate noise between Computer and Dac - Solved!

post #1 of 4
Thread Starter 

Hi Guys,

 

I just stripped the center of a Usb cable, and cut the black wire, isolated it using electrical tape so both ends don't touch, and there is no more interference when I move the Mouse or scroll, All great!

 

But.. I can hear a slight high pitch sound, very faint, that lasts approx. 15 seconds after each time I play and stop something, ie - Open Spotify, play a track, and press stop, slight whine through speakers, then it stops.  

 

Do I need to also cut the Red 5v wire? My Dac is self powered (Musical Fidelity M1).

post #2 of 4
Thread Starter 

Cut the Red Wire, Noise still plays. It doesn't just appear after I stop the sound, its while the Usb is active. What could be causing the noise? 

post #3 of 4
Thread Starter 

Update :

 

Cutting away all isolation wires, ground (black wire) and power (red wire) on three different Usb cables removed the ground loop noise produced when there was activity on the computer, but caused a constant whining sound when the Usb was active (sound being played). Not ideal.

 

Cutting the ground wire on the input end of a balanced Xlr cable (pin 1 at speaker end) and using an untouched Usb cable removed the ground loop.  However using a Usb cable with no ground/power with ungrounded Xlr cables still caused noise when the Usb was active.

 

Conclusion - If you have powered monitors with Xlr inputs, use a Usb Dac, and suffer from noise in your audio, cut Pin 1 (male end) of the Xlr balanced cable, this should break the loop.  It did with mine!

 

I was confident I wouldn't have to spend a fortune on a Usb Isolator, and I was right.

 

The steps I took, with the solution in Bold :

 

Computer > Headphone out via internal soundcard output = No noise present in Headphones

 

Computer > > Usb > DAC > Headphone output = No noise present in Headphones

 

Computer > Usb > DAC > (Xlr balanced) Active Monitors = Noise Present in Speakers if Usb mouse/keyboard being used

 

Computer > Usb (no ground/power/isolation in cable) > DAC > (Xlr balanced) Active Monitors = Noise no longer present if Usb mouse/keyboard being used, but noise is now appearing when the Usb is active, i.e - playing a sound, and stops roughly 15 seconds after playback has stopped.

 

Computer > Usb (no ground/power/isolation in cable) > DAC > (Xlr balanced with ground - Pin 1 lifted at speaker end) > Active Monitors = Noise no longer present if Usb mouse/keyboard being used, but noise is now appearing when the Usb is active, i.e - playing a sound, and stops roughly 15 seconds after playback has stopped (same as above).

 

Computer > Usb (Untouched Usb cable, not modified) > DAC > (Xlr balanced cable with ground - Pin 1 lifted at speaker input end) > Active Monitors = Noise no longer present if Usb mouse/keyboard being used and no longer present if Usb is active.  Dac > Headphone out = No noise, Dac > Active Monitors = No noise. 


Edited by fluidz - 10/19/13 at 7:44pm
post #4 of 4
I wanted to post my own experiences to this thread. I figured that just cutting the 5v and ground could lead to stability issues, so I tried to keep a reference between my laptop and USB amp. I did this by adding a 320 ohm resistor in the ground cable and added a 10uF 50v cap between 5v and ground to make the 5v a bit quieter. Adding a 100nf cap as well would have been perfect, but I didn't have any laying around.

The result looks quite messy, but sounds really good and quiet. At least better than just cutting the gnd cable.
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Head-Fi.org › Forums › Equipment Forums › Cables, Power, Tweaks, Speakers, Accessories (DBT-Free Forum) › Usb Cable, cutting Ground (black wire) to eliminate noise between Computer and Dac - Solved!