When it comes to audio most revisions of the model 1 sega genesis have the best audio. I didn't realize that there's a difference in audio quality between the genesis 1 and the genesis 2 until I picked up my first model 1 (a va5 japanese megadrive, one of the best revisions). Amazingly the audio sounded so much better on the model 1. I even made a video showing the difference in audio quality:
http://www.youtube.com/watch?v=hOOrv9e5 ... ideo_title
The next step was to look at improving the video quality of the system. I first externally encoded the rgb to s-video which looked pretty good but not perfect. Then I tried doing the s-video mod to the cxa1145 chip that came with my genesis. I tried 2 different s-video circuits both worked but they came with different types of distortion.
It seems that the cxa1145 video encoder is a crappy chip (in general). On most tvs and capture devices you don't see the distortion that this chip creates but my capture card picks up all types of distortion and with the cxa1145 it's quite obvious. Even when I was externally encoding the rgb from the cxa1145 to s-video I was still getting the same kind of video distortion.
The logical next step to take was to replace the cxa1145 with something better. I didn't have anything better sitting around for a while so this project got put on the back burner. I also realized a while ago that the popular cxa1645 sony encoder isn't pin compatible with the 1145. In fact the 1645 needs a very different circuit to be built for it to work.
I'd been building kits for av famicoms to install into nes/famicom systems for people as commission work. The kit I use is from here:
http://homepage3.nifty.com/F-LABO/ProductsList.html
After studying the kit for a bit I realized that the video circuit on the kit is basically a completed cxa1645 circuit that also uses a lm1881 to clean up the sync before the sync is fed into the cxa1645. So I came up with this great idea to try wiring this kit into a model 1 genesis.
I desoldered the cxa1145 from my model 1 genesis and installed a precision socket where the 1145 used to be sitting. Then I connected the rgb + sync input pins from the precision socket to the rgb + sync input pins on the cxa1645 kit. The kit is powered by 5v from the 5v pin on the av famicom ppu socket. The genesis has a 5v pin on the av port on the back so I wired up the 5v pin to power the kit and grounded the kit to the genesis. Turned on the system and everything worked 100% first try.
The video quality is much improved between the cxa1145 and the cxa1645. This mod will work on any system that uses a cxa1145 (sega master system, neo geo AES) assuming that the system has 5v that you can tap from somewhere on the pcb. Here's the comparison screenshots between the 1145 and the 1645:
