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As many high end graphics card have high frequency coil whine and my particular one is causing whine on my diy studio monitors, what would be the best way to filter this noise?

My studio monitors are powered by 24v 750mAh DC adaptors (each) which I suspect aren't properly filtered. Audio signal is carried from Sound card by stereo cable. When using headphones, there's no noise. When I use a different audio source to the monitors, there's no noise. When I exit any GPU intensive application (gaming/rendering) the noise disappears. So that rules out any troubleshooting. High frequency noise is jumping from the graphics card over to my diy monitors.

My proposed solution:

  1. 4,7uF ; 0.1uF ; 0.001uF Bypass filtering capacitors rated at 60V connected in parallel on my 24vDC voltage input.

  2. 1:1 600 Ohm Audio Isolation transformer on my input.

Please criticize and give a better solution if you have one.

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  • \$\begingroup\$ What do you mean "high frequency"? In the audio band, like 15kHz? It could also be aliasing noise from a higher frequency, such as 30kHz. \$\endgroup\$ – rdtsc Jan 25 '16 at 14:14
  • \$\begingroup\$ Sounds like bad grounding techniques to me. They likely just tied the digital ground to the analog ground without a second thought. FakeMoustache's solution is correct, or if you're into modifying things, I'd separate digital and analog ground with a ferrite bead or through a very thin "zero ohm" trace. \$\endgroup\$ – Dave Jan 25 '16 at 15:14
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I do not see how adding caps to the 24 V line would help. The noise appears to be entering through the audio connection from the PC. Decoupling the 24 V for the monitors seems pointless to me.

Regarding Audio isolation transformer: this could help if grounding is a problem. But if the noise is already present in the audio signal, the isolation transformer will not help.

But let me suggest a different solution for you which I use myself in combination with a high-end Headphone in order to prevent all audio issues.

I use a separate audio DAC, you could use this model, (mine is a different one with a headphone amplifier) and connect it optically (with a TosLink cable) to your PC. That is assuming your PC has an optical output. If your PC has a digital SPDIF COAX output, you could also use that.

If you do not have optical or COAX digital outputs on your PC you could get a USB soundcard like this one, this is the actual model I use.

I use the optical connection because it gets rid of any grounding issues. Also the audio signal does not become analog before it is outside the PC.

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  • \$\begingroup\$ The noise isn't present in the audio signal. The monitors behave like this even when the audio jack is plugged into say a phone playing an mp3. As soon as the GPU starts crunching, the high frequency carries over. When using headphones even turned up all the way, it doesn't carry over. \$\endgroup\$ – RyanRulingRama Apr 5 '16 at 9:27

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