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View Full Version : Guide to SNES SCART audio grounding quick-fix



opt2not
12-09-2014, 02:35 AM
So if you've bought a SNES SCART cable, and noticed quite a bit of hissing noise coming out of your speakers, especially when there's a lot of white on the screen, then your cable's audio ground could be sharing it's ground pin with the video.

That was the case with mine, until I decided to do something about it. Instead of ordering a new one, I wanted to modify the cable myself and save a little time and money.

Reading some forum info, and getting in touch with Robert at retrogamingcables (where I initially bought this from a little while ago) it was concluded that the issue was to do with GROUND sharing.
The SNES has 2 ground connections, but in my cable only one of them was connected to the SCART end which was being used for everything else as well.
http://kyorune.com/modding/file.php?art=12&file=1

Robert informed me that my SCART cable had an unconnected yellow wire (composite video) which is redundant in this cable, that I can used as a new separate ground wire for the audio.
Simple enough...onto the fix then!

Getting into the MultiAV plug is a bit tricky, but with a little patience, you can open up the housing fairly cleanly.
I used a box-cutter, and a sharp x-acto knife.

First, score the side of the multiAV plug along the glued crease on both sides with your x-acto knife:
http://i.imgur.com/xcFc2IE.jpg

This is a time consuming step, but if you want the cut to be clean, then I suggest scraping away the plastic multiple times to get a deep enough crevice. You want this on both sides (I use this method when cutting plexi/lexan for arcade bezels -- score and crack)

Scratched away enough material on one side so you can cut right through into the housing. Next, insert the Box-cutter blade and carefully and slightly twist it, to free up the sides from one another, this should crack the housing along the scored lines:
http://i.imgur.com/DT6TSeP.jpg

If you scored cleanly enough, it should be a straight enough break once you've opened it. Remove the housing completely so you can get at both side's pins:
http://i.imgur.com/07WZO0f.jpg

http://i.imgur.com/lwiS7n5.jpg

You will need to de-solder PIN 9 from the MultiAV and solder into the spare ground PIN 5.
http://i.imgur.com/xPhO9NP.jpg

Then on the scart plug end take the yellow wire which is now connected to the spare ground, and solder to PIN 4 on the SCART end. I put some heat-shrink tubing to insulate it.
http://i.imgur.com/1UsF1PI.jpg

After that, put the Multi AV housing back on, glue it or tape it together, whatever you prefer. The results will be quite a difference in audio noise. Though minimized, I noticed there is still a little bit of hissing there, but it is definitely a lot better. I could probably reduce this even more if I used shielded wire for the audio connections, but that would require me to radically change the cable, which I didn't really want to do at this point. But for now this works fine.

I hope this helps!

Yodd
12-09-2014, 07:22 AM
Hmmm interesting.

Aren't ground pins 5 and 6 on the SNES multi out electrically attached to the same ground point? I would think there would be continuity between the two.

But cool if that helps reduce noise.

Combine that with multicore coax cable and it should really help.

ballzdeepx
12-09-2014, 07:34 AM
Nice detailed guide, Ill need to try this.
Thanks for sharing.

Mercuttio
12-09-2014, 02:54 PM
I recently ordered a replacement Euro cable for my SNES... I'm switching from Japanese RGB 21 to Euro SCART for switchbox reasons, and I'm hoping to avoid this problem this time around. The sound on the old cable drove me NUTS.

I bought this one:
http://www.ebay.com/itm/201216661671?_trksid=p2059210.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

And it claims the following:

This is the fully grounded version of the cable. Most third party cables for Nintendo products sold on eBay lack shielding inside the cable and grounding wire connected to this shielding at both ends. We connect ground wires to five points in the SCART as well as both ground points in the Nintendo multiout. This results in a significant improvement over cheap mass produced cabling from most other sellers and is necessary to cut out audio buzz.

Will I need to disconnect one of those ground points to get the best audio, or is having both connected a better situation?

Mercuttio
12-09-2014, 03:02 PM
Oh, duh, I see. That wire you disconnected was the unused sync. Sorry!

opt2not
12-09-2014, 03:14 PM
Will I need to disconnect one of those ground points to get the best audio, or is having both connected a better situation?
I've been told that the RetroGamingAccessories cables are properly shielded and grounded, but I don't own those cables since I bought mine from Retrogamingcables (bah these names are too similar). Maybe someone else can chime in here who has the RGA cables?

Personally I try to avoid ebay as much as possible, which is probably why I went with the RGC ones in the first place.


Oh, duh, I see. That wire you disconnected was the unused sync. Sorry!

It was the unused Composite Video wire. Not the sync (which is being used).


Aren't ground pins 5 and 6 on the SNES multi out electrically attached to the same ground point? I would think there would be continuity between the two.

But cool if that helps reduce noise.
Yeah perhaps you're right, but I haven't verified this yet. I should just open up the SNES and start poking around for continuity.

I googled this schematics pdf and it looks separate to me, but I can't read schematics too well.
http://wiki.superfamicom.org/snes/files/snes_schematic_color.pdf

Mercuttio
12-09-2014, 03:27 PM
Aha!

I made the mistake first time around of getting a cable that required the other kind of sync. I had to solder an extra connection internally for it to work.

MtothaJ
08-07-2015, 12:38 PM
After that, put the Multi AV housing back on, glue it or tape it together, whatever you prefer. The results will be quite a difference in audio noise. Though minimized, I noticed there is still a little bit of hissing there, but it is definitely a lot better. I could probably reduce this even more if I used shielded wire for the audio connections, but that would require me to radically change the cable, which I didn't really want to do at this point. But for now this works fine.

I hope this helps!

I have also had a go at tackling this issue since it was also getting on my nerves and through various trial and error type experiments concluded more or less the same. Even though the SNES is a common ground device, having the ground connected to just one or even two small points on the Multiout just does not cut it - you simply need to carry more ground over to the display to equalize the possible differences in ground potential between the two devices.
I obtained the best results by getting an ordinary scart cable, cutting of the plug at one end and hardwiring the scart cable directly to the console. This way I got the signals from the multiout, however with all those spare grounding wires I was able to grab the ground from the board in at least 5/6 places (e.g. attaching a grounding fork and placing it under a screw). Likewise on the scart plug end I made sure all the grounds were tied together. Using this method eliminated any noise / interference in the audio.
Obviously, I realise that not every one wants to hardwire a cable into their machines since it doesn't look particularly pleasing etc. so the next best option is to do what Opt2not has described but to go a step further - cut the traces and run ground (preferably using reasonably thick wires from several good grounding points on the board) to all the pins on the multiout you are not using (e.g. if you are running RGB with csync then chroma, luma and cvideo can go, likewise if you are in the USA and connecting to a PVM and not a Scart TV you don't need +5V ect. ). Obviously it helps to have a connecting plug which is fully populated in terms of pins and to use a coaxial scart cable.
While there is some hassle involved in terms of the end result it is definitely worth it.

wyo
08-07-2015, 12:53 PM
In my experience, properly wired SCART and SCART to BNC cables will result in identical sound quality to connecting via RCA composite and LR audio cable. No console modding should be necessary. Interconnecting all grounds in the cables should prevent additional interference, not cause it.

Xian Xi
08-08-2015, 11:25 PM
It's not necessarily the sharing that's the problem. It's usually the size of the ground. If it's being shared, it needs to be bigger gauge if it's a single connection.

On my custom scart cables there is 9 conductors plus the shielding. On the console side I connect two wires plus the shield together and on the scart side those two wires are for ground and then I cut the shielding to break the shield so it doesn't carry over any hum if any from the shield.