no I did not but I see where you're going with this. if I only do number one the jail bars are still there. I guess the extra ground point stops the voltage returning on the single wire to the video encoder. i'm still a bit confused about the fundamentals of what this fixes. The initial thought was that these high spikes were being generated on the amplifier output. what changed?
The noise is caused by the current going to the N64RGB modding PCB. This current needs a return path to the N64 mainboards ground. Lets say you solder just single 'long' wire (with data lines) or maybe a second 'short' wire to the MultiAV for ground connection. Compared to the four short wires for the video signals (assume that you also soldered /CS or /CS75) the one or two wires have a higher resistance.
So the current will take your wires for the video signals as the return path!
I installed two additional GND connection very very close to modding board. In that way the GND-loop becomes very small and the jail bars are eliminated
On my Terasic DE2 dev boards, which have ADV7123 DACs on them, there is no visible noise on anything. For those, ground is just ground for everything, and there's no separate ground.
Yes, terasic doesn't use separate GND planes as far as I remember. Also not on the DE1-SOC kit. But remember that you don't create a loop if you use the dev board.
I don't need it, but: Yay! Open hardware is always nicer than some single-vendor closed solution whose supply might stop at any point.
Mhhhh... Why does the Hi-Def NES and the UltraHDMI came in my mind...???