Sync interference

[Beaps]

Hi all

OK I am trying to make my own Saturn2jamma connector. If I wire say a the RGBS from a regular scart I get a picture but it's very dull. I decided to include an RGB Amp like the ones on the PC ENGINE and the pic looks lovely.

Now the problem I have is as soon as I add audio to the mix it's I get like a noise on the screen. It's only very slight but it's visible and it's any annoying as hell. I think it's maybe because they are sharing the same ground maybe?

How I have the audio wired up is the audio L/R and the same ground go into my amp so I am thinking maybe something to do with the amp maybe.

I hope this makes sense but any ideas to sort the wobble/noise would be great.

[buttersoft]

Unshielded or improperly shielded SCART cables are common, so it could be that producing the audio interference. I prefer to run separate audio when I can. It might also be a ground loop problem, though without seeing the precise wiring schematic of your cable/setup that's just a guess. Google it, or star grounding. SCART sockets normally have every ground wired together, it's expected, but I'm not sure about the Saturn end. Could even be that something *isn't* grounded, you never know.

FYI jamma doesn't use the same 0.7Vp-p RGB standard as SCART. Doesn't really have a standard, could be anything from 0.7 to ~4.5Vp-p. That's why arcade monitors have pots with big range, but it's not always big enough. Hence the amp.

[Beaps]

I linked up all the video grounds so pindar 4, 5, 9, 13, 17 & 18 and I am getting a much better signal but if I look close at a static letter say, I can see slight interference still

[buttersoft]

I linked up all the video grounds so pindar 4, 5, 9, 13, 17 & 18 and I am getting a much better signal but if I look close at a static letter say, I can see slight interference still

Ground loops never seem to affect SD TV stuff for me anyway. Probably a shielding issue/cheap cables then. You could try more expensive cables, but that's no guarantee things will be perfect. You could also try splitting the audio off as soon as you can. Get it right away from the video/sync signals. That might help. Beyond that, tracing interference in analog video is something of a black art.

[viletim]

OK I am trying to make my own Saturn2jamma connector. If I wire say a the RGBS from a regular scart I get a picture but it's very dull. I decided to include an RGB Amp like the ones on the PC ENGINE and the pic looks lovely.

Now the problem I have is as soon as I add audio to the mix it's I get like a noise on the screen. It's only very slight but it's visible and it's any annoying as hell. I think it's maybe because they are sharing the same ground maybe?

A video amp for cable driver and a video amp for an arcade monitor are very different. You can't really substitute one for the other. Your cable driver amp has a high impedance input which means your video signal will be unterminated at the far end of the cable. I think this is why the audio is interfering with it. Unfortunately, if you terminate the signal (connect a 75 resistor to ground for each video line) your video will be dim again because a cable driver amp never has a gain of more than two.