I tried building a RGB to composite/s-video converter using the AD725, using the schematic on this page:http://www.engadget.com/2006/11/28/how- ... cade-game/
But, it produced a very poor quality image that was almost unrecognizable. I didn't bother troubleshooting it, I just bought a converter. Pre-made converters are nearly the same cost as building the AD725 circuit.
RGB to composite/s-video $25http://www.arcadespareparts.com/arcade_ ... 12217.html
RGB to VGA $35http://www.arcadespareparts.com/arcade_ ... 13052.html
If you have a TV with a VGA input, the VGA converter has better compatibility and picture quality, so I would go with that.
Also, I made a wiring diagram of my SuperGun system.
Only the component side of the JAMMA connector is shown, the solder side is nearly identical (minus the video and sound.)
The DB15 connector is fully compatible with NeoGeo controllers, or build your own controller so it has 6 buttons for fighting games ( plus a start button.) I used 2 unused pins on the DB15 connector for wiring the 6 and 7 buttons. Most JAMMA boards only support 3 buttons on the connector, if more buttons are needed they are connected using the appropriate kick harness.
The DB9 connector is for connecting a kick harness to use buttons 5-7 and/or stereo sound. This way, you can easily swap out games without tedious wiring of the kick harness.
Aside from soldering lots of wires, building your own supergun is surprisingly simple.