SNES scart cable =buzzing audio

[cyb]

Hey all,

I have an NTSC SNES, and I use an RGB scart cable and plug it into an rgb to yuv transcoder. modded the transcoder to have audio out, and there
would be a very annoying buzzing sound whenever I played the snes.

I added rca jacks on the SNES thinking if I pulled audio directly from the snes board I wouldn't have any more buzzing issues. (this worked when I was having the same issue with my duo-r.)
But even if I take the audio from the rca jacks, the sound still buzzes as long as the scart cable is plugged in to the multiav port. it will buzz even if the scart end isn't plugged in to anything.

I ruled out the possibility of it being the RCA jacks at fault. I plugged in my s-video cable and the sound was fine, no buzzing. is there anything I can do about this or do I just have a crappy cable? I appreciate any help you can give me on this.

[Link83]

Sounds like a grounding problem of some kind? I would open up the Scart plug and compare the wiring to the diagrams on the main page/wiki, also looking for any bad connections. If the problem is not in the Scart connector it could be in the other end - the multiav plug, which can be abit trickier to open.

[viletim]

Does the buzzing sound change with the video content and dissapear when video cable is unplugged from the SNES? If so, cut the audio traces on the SNES PCB which go to the multi A/V connector. Connect your RCA sockets to the other side of the traces.

[cyb]

Does the buzzing sound change with the video content and dissapear when video cable is unplugged from the SNES?

Yes.

For example, if I play super mario all stars, the sound buzzes on the title screen. after I press start, the screen goes dark for a moment, and the buzz disappears. the buzz then returns when the game selection screen pops up. 

[Drakon]

I had that problem with mine.  I stuck 100uf 10v capacitors on the red, green, blue, and sync wires and the buzzing is gone (it also fixed the sync problem I was having).  Apparently ntsc sfcs and sness have extra voltage going through the lines.

[cyb]

looks like the cable i have already has those 100uf caps on there... I suppose ill try the cutting traces method when I get some time to do so.

[cyb]

problem solved. pulled audio off of the apu instead of the multiav port and the buzzing is gone. there is a light humming but its barely noticable, much better than the buzzing. I appreciate all of your help!