supergun jamma sound interferes image

[InspecteurZ]

I'm working (again) in a simple supergun to connect jamma to tv. It uses a standard atx psu, neogeo controllers and scart cable. If I don't connect sound to the scart cable all seems to work ok, but with sound attached the image gets interferences that follow music beat (!)
I'm wondering if can be because all grounds are wired together.

[Blaine]

What game are you hooking it up to and how many amps is the power supply?

If this were happening with a console system, my guess would be that you weren't using the proper power supply. In theory the psu should provide more than ample amperage, unless you're driving monster speakers.

[ken_cinder]

I'd bet money it is totally unrelated to power supply, I had this happen to me when wiring up a set of PC speakers to my PSONE LCD in an arcade related project.

Simple answer. The speakers are rated lower for resistance than the amp you are driving them with (I was using 4ohm speakers, the original ones on the PSONE LCD were 8ohm, 4ohm resistor(s) on the positive lines solved it)

Could be a second issue in that nearly all Jamma and Jamma based boards, output amplified audio. You CANNOT feed this to a line input like on a TV or tuner. If this is the case, start out with some 10k resistors on the positive lines and work your way up or down in resistance until you achieve a useable signal (This isn't the best way, you SHOULD build a line converter, or buy one........but it works)

[InspecteurZ]

Power supply is 300w. I tried some konami (MIA and metamorphic force), cps1 and an old toaplan jamma.

I'll try using external speakers and/or putting the resistors.

Thanks.

[RGB32E]

Use a high level to line/low level converter.
http://www.caraudiodeals.com/audiopipe-nr100-high-level-rca-line-level-converter-p-732.html

I picked up a unit like this (same functionality) and use it for all of my arcade boards that do not have line level audio output.  It cleans up the sound (no pops on peaks) and makes it safe to connect the audio from arcade pcbs into a tv or stereo (line level audio input).

For my setup (modified MAS from '97):
1. Removed the converter pcb from its case an wire leads.
2. Connected the JAMMA Speaker + and - to the appropriate terminals on the converter PCB
3. Connected the output terminals from the converter PCB to RCA output jacks
4. Adjusted the trim pots on the converter.

Note. For some reason, MAS Systems thought it would be a great idea to wire speaker + and - to the respective center pins of the rca connectors (for L and R), and connect ground to the ground connection.  I suppose this would be fine if you're just using the audio output to drive speakers with a Neo Geo MVS (connected to RCA terminals), but could potentially damage audio equipment... 

Anyways, using a high to low level converter works really well for arcade boards that don't have low level audio output. 

[viletim]

Those converters contain a transformer and a resistor divider. There's no other 100% safe way to connect speaker -> line. The -ve speaker connection does not necessarily have to be ground, it can be driven in the opposite direction of the +ve connection (called a bridge amplifier). If you connect a speaker -ve connection to ground in this case you may well damage the amp!

[XianXi]

You should be running video ground from pin 14 and the rest you can have together. That's what I did on mine and I have no interference.

[RGB32E]

You should be running video ground from pin 14 and the rest you can have together. That's what I did on mine and I have no interference.

+1;  I use ground from pin 14 as well and have not encountered the issue.