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Very weird problem: sound card interference with graphics card, only when line-out to external amp

post #1 of 8
Thread Starter 

Hi guys, I've been experiencing a very weird problem with my sound card and external amp, and have done a lot of testing to try to isolate the issue but still cannot figure out why. So I'll describe everything in detail and I'm hoping that one of you could tell me what's wrong. Thanks in advance.

 

My gear setup: PC sound card (Creative X-Fi Titanium HD and ASUS Xonar Essence ST, problem with both) RCA line out -> Little Dot MK III headphone amp -> Sennheiser HD-650, all connections with premium shielded RCA cables

 

Problem: whenever my graphics card (GTX 680) gets any amount of load, I get a background interference sound (hissing/buzzing) through the headphone out of the LD amp. The amount of noise seems to be proportional to the level of GPU load (maximum when GPU is at 100% load, monitored through GPU-Z).

 

I have tried/found:

  • Started with Titanium HD, problem occurred, and I thought maybe it's a shielding issue, so I made a custom aluminum foil based shield and wrapped it around the card. No improvements
  • Switched to Xonar  Essence ST (PCI version, with complete Creative driver uninstall with driver sweeper prior to clean install of Xonar driver). Same thing happened
  • Switched to Xonar Essence ST's built-in headphone out (taking the LD out of the loop), no interference (problem gone)
  • Back in the LD amp's headphone out, this time with the amp's power connected to a separate circuit (separate from the computer) in the house (routed from another room). No improvements
  • Switched the LD's input to my iPhone, no interference when GPU is at full load (problem gone)
  • UPDATE: Using the Xonar headphone out (which is clean when connected straight to headphones) to LD's RCA input then using the LD's headphone out, same interference problem confused.gif
  • UPDATE: Using my Pico external USB DAC/Amp connected to the computer USB, then feeding the Pico's headphone out to the LD's RCA input, same interference through the LD's headphone out, but noise volume seems to be lower; headphones connected straight to the Pico get clean signal though, no noise

 

I am seriously puzzled as to why this is happening. The fact that the headphone out of the Xonar is clean makes me think that it is a problem with the Little Dot, but then when I connect the amp to my iPhone output, it's clean again, which means it is not picking up wireless interference from my computer.

 

UPDATE: so basically it seems that whenever I have output from my computer (internal and external) to the Little Dot, I get interference when the GPU is on load. Both computer and LD together causes the issue, taking away one of them and the issue goes away (e.g.  computer sound card out to headphones directly is fine, iPhone out to LD is fine). I have been thinking getting an external DAC, but the test with the external USB DAC is making me doubt whether that would work. Perhaps optical output to a supported external DAC would help, but I am no longer as confident as before after testing with the Pico DAC.

 

Right now I'm thinking of 2 possibilities:

  1. The DAC stage of the sound cards are getting interference from the GPU, but the Xonar's headphone amp stage is able to somehow filter this out while the Little Dot picks it up. Sadly if this is the case there is nothing that can be done (both cards are shielded already and I've tried to shield it even more with my makeshift aluminum wrap)
  2. A ground-loop problem with the Little Dot, the ground level of the RCA input becomes different from the ground level of the amp power input when my computer draws more power (due to GPU load). I will try to pick up a 3-prong to 2-prong adapter for the amp tomorrow to see if this is the issue. I have ruled this out as ground loop problems happen only when devices are NOT connected to the same power outlet, but all my devices are on the same surge protector

 

I was wondering does anybody running a setup similar to mine has experienced similar problems. Also if anybody has any idea as to what the issue might be, please help me. Thanks again.

 

UPDATE 2: I have confirmed that this is indeed a ground loop problem with the Little Dot. I bought a cheat plug today (just for testing), 3-prong to 2-prong power adapter (removing the ground plug of the LD), and the noise is completely gone. Obviously I won't run with the cheat plug because it is very dangerous, but at least this confirms the problem. I will either go for an external DAC (must use optical input because USB is affected by the ground loop problem), or get a ground isolator. Thanks for everyboddy who replied!

 

PS: Anybody who has suggestions/experience on how to eliminate ground loop noise, please feel free to let me know!


Edited by Jd007 - 7/2/13 at 5:05pm
post #2 of 8

Did you "disable" (in the BIOS) the motherboard's on-board audio?

post #3 of 8

Power supply? Do you have any other GPU?

post #4 of 8
Thread Starter 
Quote:
Originally Posted by PurpleAngel View Post

Did you "disable" (in the BIOS) the motherboard's on-board audio?

Yes I've always had the on-board audio disabled in the BIOS

 

Quote:
Originally Posted by TimPrice View Post

Power supply? Do you have any other GPU?

I have the Corsair AX750 PSU, which is a very good quality 80-Plus Gold PSU. I do no t have any other GPU, just a single GTX 680, so I cannot test whether this happens with my card specifically unfortunately.

post #5 of 8

If there is interference only when using an external amplifier, then it is very likely a ground loop problem. Some possible solutions are:

- using only the Xonar ST's built-in headphone amplifier, which should be able to drive the HD650 fine (I would choose this one)

- replacing the Little Dot with a different headphone amplifier that is not grounded (does not use a 3-prong connector)

- using an external DAC with galvanic isolation from the PC (use the Titanium HD with optical S/PDIF if you need the DSP features) - the most expensive, but also most "audiophile" solution

- isolating the PC sound card from the Little Dot with an audio transformer (this is relatively expensive if you want a good transformer, and may slightly degrade the sound quality)

- not grounding the Little Dot (a cheap, but potentially dangerous solution that is not recommended at all, and is listed only for completeness)

post #6 of 8
Thread Starter 

Problem found, updated original post.

post #7 of 8
Quote:

Originally Posted by Jd007 View Post

 

I will either go for an external DAC (must use optical input because USB is affected by the ground loop problem), or get a ground isolator.

 

For USB DACs, there are USB isolator devices available for about $50 or less. Some DACs may already have USB isolation built in, such as the Music Streamer II/II+ by HRT.

post #8 of 8
Thread Starter 

How to make sure that the DAC and amp does not form a ground loop though? PC can be separated from the audio system with optical output, but with DAC to amp, unless you go balanced, you have to connect with grounded cables which will form a loop again (unless one of the devices is not grounded with a 3-pronged plug).

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