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EMI Interference

  • Homebuilt
  • Graphics Cards
  • Systems
Last response: in Systems
June 1, 2011 12:12:23 PM

Hi Everyone,

I posted a problem here before with a problem i had and got the solution! so thanks again to those who helped with that!

I have another problem. EMI. Has anyone experienced electromagnetinc interference problems with graphics cards? I have an EMI problem and i suspect my graphics card to be the cause.

I am a guitarist and i have two separate sound setups on my computer. one for regular audio and one for recording. The regular audio setup involves a speaker set with four speakers and a subwoofer and is connected to the motherboards sound output. I have absolutely no problems here, its all fine and sound is very good.

Where i am experienceing the problems are...
1) In my guitar amp. When i play guitar with high enough gain and distortion i noticed it picking up what sounded like digital noise.
2) Separate from my everyday audio setup i have a recording setup. This includes an Edirol FA-66 firewire audio interface. 2x Mackie MR5 active studio monitors.

Here is why i suspect it is caused by the graphics card. There is a constant EMI digital sounding noise present but anytime an image or graphic changes on the screen it changes the sound and makes it louder while the image or screen is changing.

I have disconnected the HDMI monitor cable, no change.
I have unpugged the monitor and removed the DHMI cable, no change.

When the interface is turned off the studio monitors don't pick it up, BUT even unplugging them from the sound card results in the noise going away, so the studio monitors only have the noise present when plugged into the firewire interface. They are connected with TRS balanced cables. Obviously they need to be connected but i dont think its the interface causing the problem because when the soundcard is turned off or the firewire disconnected, the noise is still picked up by my guitar amplifier but only when a guitar is plugged in, e.g. the guitar is picking it up, so its still there.

I had a wireless mouse but with that disconected and powered off its still there.

So its not caused by motherboard sound as its not present on my normal speakers, not the monitor cos its still there when thats removed, not my soundcard as far as i can tell because when thats removed the guitar amp still exhibits the symptoms, not the mouse or keyboard. I tried attaching a ferrite core to the firewire cable too but had no effect.

I'm pretty sure it must be the graphics card. I haven't ruled out the possibility of a ground loop either but it seems more likely to be gfx emi. The power connecter to the gfx is a 6pin connector and i checked to see if it had a ferrite core and it did.

The graphics card is a GIGABYTE hd5770. My brother has XFX (i think) 5770 but wont let me swap em around to see. Has anyone ever heard of or seen this kind of thing before? Its really driving me mad!

Any advice would be greatly appreciated! sorry for such a long post and i hope this is the right section. it seemed the most appropriate.

More about : emi interference

June 1, 2011 1:34:59 PM

Hmmm just did some online reading and heard reports of harddrive noise causing problems. I suppose when graphics and images change they could be loading from the harddrive, as in virtual memory? I ran HD tune and everytime the graph updated i was getting a change in the noise. It also happened with the window minimized. Does this suggest its hard drive noise being picked up?
a c 113 B Homebuilt system
a b U Graphics card
June 1, 2011 8:54:32 PM

Actually, the first suspect would be the PSU. There is a great deal of potential for noise there, and as load demands vary so will the noise generated by the PSU. If you list your parts I can make a better guess.
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June 1, 2011 10:42:48 PM

The PSU? Really? I would have thought power supplies for computers would be designed to eliminate such problems? suppose anything can happen tho!

Oh yes, i should have listed the parts.
PSU: Thermaltake Toughpower 750watt
Motherboard: 790fx + SB 750 (cantremeber the exact model number. IIRC its an MSI board. the one with the overclocking buttons on it, and 4 PCI-E slots)
CPU: AMD Phenom II x4 965 BE
GPU: Radeon HD5770 (gigabyte)
RAM: Patriot Gamer Series 4GB (2x 2GB) PC3 12800 1600 MHz DDR3
HDD: 2x 500gig RAID0 (Cant remember which tbh! i think 2x samsungs)

External components
FW interface: Edirol FA-66
Studio Monitors: Mackie MR5's
Speakers: Dell Speaker set.

June 1, 2011 11:08:48 PM

EDIT: Sorry, motherboard is actually MS-7577-010 MSI 790FX-GD70 AMD motherboard.
a c 113 B Homebuilt system
a b U Graphics card
June 1, 2011 11:35:59 PM

The original Toughpower had some issues I think.

If it's an original Toughpower it's getting a bit old and might well have some issues, given the build quality of that sample.

If it's a newer XT model it's much less likely to be the problem, but still could be.

Do you have any PSU you could swap out?

Also, just re-seating all your connections is a good idea if you haven't. A poor contact would do it for sure.
June 11, 2011 2:51:39 PM

Hi Proximon,

Appologies for the delay in replying. I was away on holidays for a week.

Yeah its a newer XT version but will def read thru that article (I just finished college studying electronic engineering so the talk of filtering and stuff looks very interesting!)

Again, my bro's computer is the only source i have for changing out parts for testing but he's not keen on my opening it up! I didn't built the computer,i bought it off a guy who had built it a few months before, so I will more than likely have to tidy up some of his wiring anyway so i could see if that helps and reseat connections while i'm at it and see if that helps.