[Callan Brown] wrote in to show us a really interesting NES audio hack. [Callen] decided that he wanted the full Castlevania III audio experience, which (without modifications) can only be had through the original Japanese Famicom console. [Callen] weighed a few adapter options, and instead decided to come up with his own.
The issue is that the Japanese Famicom and the American NES actually have a different cartridge connector. The change in hardware from a 60 pin to a 72 pin connector added “features” like the 10 pins connected directly to the expansion port (used for stuff like the teleplay modem, who knew). The other two additional pins are used by the annoying 10NES lockout chip. While they were at it, Nintendo decided to route the audio path through the expansion connector instead of the cartridge.
This means that the Japanese cartridges can’t pipe sound to the NES audio channel with just a pin adapter. Good news though, after sourcing a pin adapter hidden inside certain NES games (Stack Up, Gyromite), audio can easily just be pulled from the adapter PCB. This requires the more expensive Famicom Castlevania III cartridge (Akumajou Densetsu). To cleanly route the new audio cable out of his front loading NES [Callan] reuses the sacrificial adapter game’s cart to make some kind of unholy hybrid. To round it off [Callan] also goes over steps to flash a translated ROM to the Japanese game.
What difference could an extra two squares and a sawtooth make? Check out the sound comparison video after the jump! Thanks [Callan].