Yeah, the cartridge pinout is slightly different. The famicom has a 60 pin connector and the NES has a 72 pin connector, but ten pins go to the expansion port and four pins are used for the license chip, so two pins were lost, and those two pins were the audio out/in. Castlevania (and some other games) has significantly different audio for Japan vs the rest of the world.
There's a few different ways that people modify their NES if they want to use cartridges with audio hardware, using the (otherwise unused) expansion port pins.
Yeah I've seen some youtube vid about famicon audio chips and it was insanely high fidelity for a tiny video game console. Must be weird to play such games as a kid back in the days.
There's a few different ways that people modify their NES if they want to use cartridges with audio hardware, using the (otherwise unused) expansion port pins.