In Hardware

Some Famicom titles, as well as the Famicom disk system, use pins 45 and 46 on the cartridge connector to transfer their enhanced audio to the famicom.

When you connect these carts to an American NES with an adaptor these pins are either not connected, or are connected together and the enhanced audio is not heard.

The NES Expansion port has two pins label Audio in and Audio out just like a Famicom cartridige connector. Are these pins compatible? That is, if I connect pins 45 and 46 to these two pins on the expansion port will the enhanced audio be heard?

Also, I know pins 45 and 46 pertain to audio on the famicom cart, and pins 3 and 22 on the expansion ports do also, but beyond that I'm not sure which are inputs or outputs. Some clarification as to what goes where would be appreciated.

Honestly, I've never looked too much into the Famicom. There's some documentation you can look at here though:



... and...



I'm not sure if you've already been to those sites, but if not, I'm sure you can find some info that will help you in some way.

Nope, looked all up and down. Maybe I missed something. Oh well if I can't find anything, or if no one knows, I have an NES I was going to gut anyway. It can be my test unit. Now all I have to do is find a Japanese copy of Castlevania III to test my results with.

There are actually several Famicom carts that have enhanced audio, just about all games using the Konami VRC6 mapper, Lagrange Point which uses the Konami VRC7 mapper (and produces some amazing FM syth tunes)

You might want to look for:

VRC6:
Akumajou Densetsu
Madara
Esper Dreams II

VRC7:
Lagrange Point

SunSoft FME-7 (AKA Sunsoft 5):
Gimmick!

I've also been quite interested in the enhanced audio of those Famicom carts for quite some time, I didn't know that it would be bypassed if played on an NES. So I'm quite curious to learn what you discover.

I'm assuming that it's a regualr analog audio signal coming directly off the cartridge pins. If that's so then even if the audio in and out on the expansion port won't work you could still mix it in with the audio some other way.

Ok, I pulled out a spare NES I had in the attick. I have 3 so if one bites it I still have two others. Also this one is donating it's housing for an NES PC eventually anyway.

I soldered a wire to pin 3 on the expansion port which is labled Audio in. I then attached another wire to ground. I had a scrap of wire also that had an ear phone plug on it. I attached this wire the wire I soldered to pin 3, and to ground. Using my DS and Movie player as the sound source I pluged the wire to the DS earphone port. I inserted Super Mario Bros. and turned on the POWer. The results were both good and not so good. I could hear the DS, IF I turned the tv and the DS all the way up. So while I have determined that pin 3 on the expansion port is an audio input I have not determined yet how to make it loud enough to hear. Perhaps using the expansion port's ground pin would help. Not sure really. Perhaps there is some sort of amplification circuitry requried to mix audio with the NES audio. I haven't found documentation that explains yet.


Edit: I might have some idea why it's so quiet. Pin 3 leads directly in to R9. R7 and R8 are also next to this. All 3 resistors connect to audio and mix here. Tapping in to R7 and R8 is how you do the Faux Stereo sound trick. So pin 3 IS an anolog audio input, and it mixes directly in to the NES audio. I have a fealing R9 is dropping the signal so much I can't hear it. Not sure why the audio is normally audible through these resistors when I had the DS up all the way and still couldn't hear it well. I may try to bypass this resistor and see what happens.
Perhaps the the normal signals are much stronger than a DS turned up all the way.

Edit 2: I bypassed R9. I could hear the DS much clearer. The only problem was instead of mixing with the audio it totally overides it. Apparently R7, R8, and R9 keep the audio tracks from overriding each other. I can only assume since the normal audio from R7 and R8 are clearly audible during game play then the audio from a famicom cart has the circuitry required to be audible through R9 as well. I found this diagram of the NES audio pathway:



The only thing different I can tell is the audio is grounded with two 100 ohm resistors before it gets to R7 and R8. Perhaps if I do the same with an external audio source it will be audible as well and mix with the NES audio. On to experiment #3.

Edit 3:
Kaplah!

I grounded the DS audio with a 100 ohm resistor and it mixed with the NES audio perfectly. Now if an enhanced famicom cart can't be heard I know to use a 100 ohm resistor to make it work.