In pretty much all retro consoles everything is driven by the same clock signal. However the av famicom rgb / s-video kits have the video encoder driven by a separate crystal oscillator. Driving the video encoder from the same clock signal as everything else greatly improves the video quality. The nes clock signal is 6x as fast as what's needed to drive a video encoder in ntsc mode. I worked with tiido to help me figure this out (the creator of the sega genesis crystal clear audio mod). Both me and tiido found the same schematics on the internet and tiido helped find me the right parts to use and explained the basics of how to wire the ICs up. I bought the ICs and wired them up and the circuit indeed worked right away. The difference is extremely noticable the s-video image quality now looks absolutely pixel perfect. Here's the circuit I built:
I grabbed the system clock signal from ppu pin 18 thanks to the nesdev ppu pinout sheet. Here's some comparison screenshots...it's a bit hard to notice the improvement from the screenshots but on my tv it's greatly improved:
The non portablizer! Specializing in....Video quality?