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Ground loop interference with Computer, DAC, Mixer, Speakers?

post #1 of 19
Thread Starter 

Hello everyone,

 

I've been having some issues eradicating interference from my computer audio setup. As of now, I'm using my desktop computer and a 30" CCFL-backlit computer monitor to play games and perform other tasks. For audio, I have a Fiio E07K connected to the desktop via USB, which I have then connected to a sound mixer via an RCA - 3.5mm connection. The mixer then provides a signal to 2 KRK Rokit 5s over short XLR cables. All these devices are connected to the same power strip, which is in turn connected to a grounded UPS.

 

The problem I've been experiencing is actually twofold. Firstly, I found that whenever my monitor was turned on and the backlight was on, I could hear a ton of interference/hum through the speakers, regardless of the output level of the computer. I ended up marginalizing this problem by removing the ground pin from the monitor's power cable (which had the most profound effect) and the second thing I did was increase the E07K's volume output to max and its gain to +12dB. At this point in time, I cannot determine a difference between when the monitor is on and off. 

 

My second problem is slightly more troublesome, and I'm not really sure how to fix it. Whenever I'm doing something GPU-intensive and the graphics card has ramped up in its utilization or power consumption, I can hear interference that is almost definitely caused by the graphics card. I get different styles of interference based on the scene the GPU is rendering in the video game, I can hear interference when I move my mouse cursor around on screen, and when the GPU is being utilized at 100% by Folding@Home or a mining program, I get a constant hum from the speakers.

 

I've been considering getting a ground-loop isolator for ~$13 from Amazon so I could isolate those channels coming from the DAC, but I don't know if that would help. Does anybody have any suggestions for me on what I could try or what I could buy? It's really frustrating to not be able to listen to audio without a great deal of interference, and I'd love be able to fix it! :D 

post #2 of 19

My first step would be to try a USB isolator. The most likely source of this interference is the PC power supply which makes a galvanic connection with your DAC over the USB. That will also break the ground loop if indeed you have one.

post #3 of 19
Thread Starter 

Cool! I didn't know USB isolators existed. However, they are many times the price of a 3.5mm or RCA isolator, so would it be worth it to try one of those before I get a USB isolator?

post #4 of 19

That's roughly twice the price:

http://hifimediy.com/index.php?route=product/product&product_id=122

Note that this will not handle sample rates over 96kHz...

 

I don't think the RCA isolator is going to fix it, and it may degrade the signal somewhat. I'd rather fiddle with the digital part of the signal path. 

In the end it's your call...

post #5 of 19

Aren't there also USB cables with the power lead either isolated or absent?  However, these are 'audiophile' USB cables, and might be cost prohibitive, especially if you require a longer length.

post #6 of 19
Quote:
Originally Posted by Red Jacket Mike View Post
 

Aren't there also USB cables with the power lead either isolated or absent?  However, these are 'audiophile' USB cables, and might be cost prohibitive, especially if you require a longer length.

 

Actually in my USB cable between PC and the DAC I have cut off the power lines myself, but it only makes sense if you are sure your DAC doesn't need them (some DACs are powered via usb, even when there is on-board power supply). And the data lines still provide galvanic connection between the computer and the DAC. 

post #7 of 19

I guess another easy way to determine if the interference is coming from USB or other sources would be to connect the computer to the DAC using coax or optical, if those connections are available on both.  No power leads involved there.

post #8 of 19

Coax will not help to isolate the systems - it's still an electrical connection, in that respect no different from RCA connections that are often closing the ground loops.

Optical on the other hand does provide complete galvanic isolation.

post #9 of 19

I had this issue with one motherboard and used am RCA  ground loop isolator and it worked but that was with RCA analog connection. With digital optical or coax I have never had this issue and that is what I use on my main PC now.

post #10 of 19

hahahaha.. I had the SAME EXACT PROBLEM!!! I had a pair of Rokit 8's that would hum a little when I was doing whatever and when I played a game it was really bad. I tried the ground loop thing to no avail, I tried dual XLR to 3.5 I even tried having on the same power strip and separate ones. What I ended up doing was dropping $275 on a Dual XLR out source and got 2x XLR to XLR cables. This SOLVED the problem. 

 

 

If any part of your speakers is connected using a 3.5mm plug it will hum. The reason cheap speakers and onboard audio doesn't hum on the same system is because they aren't amped. Rokit's are notoriously amped and even the faintest interference/hum will be magnified. This is why at times even when there is no sound coming out of the speakers they will hum. With XLR the wires are separate from the source to the speakers. If you turn down the dBs on the back of the rokits it should fix the hum/interference. The problem is the speakers will sound really flat and lifeless. 


Edited by Folex - 4/7/14 at 9:07pm
post #11 of 19

Always handy to have a ground loop isolator around. Even if you only use it for diagnostics and emergencies.

 

Need not be expensive and could save you a lot in time and unnecessary purchases.

 

http://cpc.farnell.com/1/1/64523-ground-loop-isolator-av19276.html

 

or a branded version.

 

http://artproaudio.com/artcessories/audio_solutions/product/dti/

 

The really good ones for stage use contain Jensen transformers similar to those used in expensive MC Phono pre-amps and can cost $400. Radial is the most common brand.

 

ed: spl:(

post #12 of 19
Quote:
Originally Posted by Folex View Post
If any part of your speakers is connected using a 3.5mm plug it will hum. The reason cheap speakers and onboard audio doesn't hum on the same system is because they aren't amped.

 

More likely those speakers are not grounded, while the Rokits are, and therefore there is no ground loop with the former.

post #13 of 19
Quote:
Originally Posted by stv014 View Post
 

 

More likely those speakers are not grounded, while the Rokits are, and therefore there is no ground loop with the former.

I've physically attached the ground from the plug to a grounded bolt by a wire. When I did this the ground read 0 when I tested it. So for me personally I doubt it was an issue.
When I went XLR to XLR it completely eliminated the problem. And these XLR cables were $10 cheapies.   I'm guessing the 3.5mm to XLR could have been at fault but I've had this problem with 5 previous powered speakers/monitors and they were all using different wires. 

 

I tested both XLR->XLR and 2x XLR->3.5mm on my xda2 amp/dac. It has both dual XLR and 3.5mm jack. Using dual XLR cables there is 0 hum/inference. When I use the 3.5mm to dual XLR the hum is back.   

 

When I used the group loop isolated the volume lessened considerably but the hum volume was the same.

 

And all this testing is done with my Rokit 8's with both knobs on back @ 0 dBs so its not a matter of being over-amped. 


Edited by Folex - 4/8/14 at 1:39pm
post #14 of 19

As long as both the speakers and the computer are grounded somehow, there is a possibility of a ground loop. Some of the ground currents from the PC will take the path through the audio cable and the speakers/external amplifier, and cause interference noise under system activity (moving the mouse, scrolling, running games, etc.). A simple DMM is not necessarily sensitive enough to detect intermittent high frequency noise that is enough to be audible when amplified. A balanced (XLR to XLR) connection solves the problem by using differential signals, and not referencing the audio input to the ground, which may be noisy (or, more precisely, the noise is eliminated by common mode rejection).


Edited by stv014 - 4/8/14 at 1:48pm
post #15 of 19
Quote:
Originally Posted by stv014 View Post
 

As long as both the speakers and the computer are grounded somehow, there is a possibility of a ground loop. Some of the ground currents from the PC will take the path through the audio cable and the speakers/external amplifier, and cause interference noise under system activity (moving the mouse, scrolling, running games, etc.). A simple DMM is not necessarily sensitive enough to detect intermittent high frequency noise that is enough to be audible when amplified. A balanced (XLR to XLR) connection solves the problem by using differential signals, and not referencing the audio input to the ground, which may be noisy (or, more precisely, the noise is eliminated by common mode rejection).

You know of a cheap dual XLR source? When I searched I had to spend $275 and its riddled with annoyances. I've gotten used too it but to suggest to others. 

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