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Old 22nd September 2013, 06:58 AM   #1
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Join Date: Mar 2013
Default Computer DC Bleed

The only solution seems to be using Toslink to DAC.

Has anyone come across a complete solution?



I'm surprised this issue continue to plagues computers..

I've had this problem on every motherboard, even the "premium" ones.

When the Graphics card pushes high load, the dc noise comes through the audio.
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Old 25th September 2013, 05:58 AM   #2
dangus is offline dangus  Canada
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Onboard sound is just for watching SFW videos in the office at lunchtime or background music. Sound cards are usually very good at rejecting power supply noise. If you have a spare PCI slot, pick up a $5 sound card from a computer recycler.
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Old 25th September 2013, 06:22 AM   #3
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Quote:
Originally Posted by dangus View Post
Onboard sound is just for watching SFW videos in the office at lunchtime or background music. Sound cards are usually very good at rejecting power supply noise. If you have a spare PCI slot, pick up a $5 sound card from a computer recycler.
My Gigabyte boards claim 108 dB s/n. I have not measured this because I'm too lazy (I do this sort of thing at work) but I assure you it's better than 80 dB. I have measured the response and it looks like a straightedge.. I had some ground loop problems (who doesn't) but after those were corrected it works outstandingly well.

G
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Old 25th September 2013, 04:03 PM   #4
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my problem isn't ground loop

it's the leaky GFX card.

Almost all high power cards do this...
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Old 25th September 2013, 04:11 PM   #5
AndrewT is offline AndrewT  Scotland
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Do you mean output offset?

Use a DC blocked input on your receiver.
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regards Andrew T.
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Old 25th September 2013, 04:16 PM   #6
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I think he means crosstalk from his graphics card into his audio through the power rails.
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Old 26th September 2013, 07:17 AM   #7
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Quote:
Originally Posted by tp4tissue View Post
my problem isn't ground loop

it's the leaky GFX card.

Almost all high power cards do this...
My 'ground loop' problem was video noise getting into the audio. It twas caused by the monitor with DVI video and analog audio. Panning the video made squeeky/buzzy noises in the audio.

The computer analog output first goes to a Niles Audio 6 out DA which feeds the monitor and 2 Technics receivers, 1 for speakers and the other for headphones. With the audio feed to the monitor disconnected the noise was gone from the receivers. The 'fix' was to 'loosen' the ground in the analog audio path by adding a small resistance ( less than 100 Ohms ) in the ground path of the analog audio. Ground loops are not just 60Hz noise.

BTW, what is a 'leaky' card? If you mean residual DC, that will not cause noise of itself and you can always add a series capacitor to block the DC component. Noise from the video card is most certainly a ground loop issue but might NOT be possible to correct at the user level without going to an external USB or optical DAC.

G
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Old 26th September 2013, 09:14 AM   #8
phofman is offline phofman  Czech Republic
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I confirm the ground-loop issue.

I had my T-amp powered by 12V from the PC, fed by decent Infrasonic Quartet analog out. I could hear every letter appearing in linux terminal, every mouse move, every key pressed.

I broke the ground loop with separate 12V linear PSU (dirt-cheap diy type) and the output is perfectly clean now, IMO very good for the total price.

If a MB is designed incorrectly, the ground loop can occur in the output buffer of the integrated card which is almost impossible to get rid of. But IMO such design fault would be more of an exception these days.
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Old 26th September 2013, 11:17 AM   #9
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What if the mouse/display/HDD/USB noises are heard only when amp+speakers are connected but no such noise is heard when head phone is connected? Then where is the fault?
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Old 27th September 2013, 10:36 AM   #10
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Originally Posted by Jack Sparrow View Post
What if the mouse/display/HDD/USB noises are heard only when amp+speakers are connected but no such noise is heard when head phone is connected? Then where is the fault?
When you connect the headphones, is the amp still connected? Do the headphones plug into the amp or computer?

G
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