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  • Joined: 22 Apr 2018
  • Posts: 208
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Game Gear Cartridge FM Audio?
Post Posted: Mon May 04, 2020 5:08 am
Has anyone tried to generate SMS FM audio in the cartridge and inject it through the TVL and TVR audio lines of the Game Gear cartridge connector?

The Game Gear has left and right audio inputs for the TV Tuner, but they work outside of TV Mode too. They still work even on McWill-modded Game Gears.

If my naïve assumptions are correct, it should be possible to make something like a Game Gear EverDrive with an embedded FM audio simulator in an FPGA and enjoy the enhanced sound tracks of those games that have one.

You might wonder why I believe it's possible. I did a potentially foolish thing: I tried covering the "\TV" pin of the TV Auto Tuner with nonconductive tape to leave the Game Gear in regular "Game Gear" mode rather than TV mode (confirmed as the unmodded Game Gear no longer displayed the video signal from the tuner's A/V connector), and noticed the audio I'm feeding in to the TV Auto Tuner's A/V connector was still audible. When I removed the tape and tried again it was back to regular TV mode, displaying the image too.

What I don't know yet is how it sounds when both Game Gear PSG and expansion port are producing audio, but luckily most SMS games with FM audio were developed for the Mark III which didn't permit these to coexist anyhow so I suspect it might work out fine.
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  • Joined: 05 Jan 2006
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  • Location: USA
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Post Posted: Mon May 04, 2020 10:04 pm
Viletim confirmed in an old post somewhere that his FM board it's supposed to work with the Game Gear. It's missing two signals though, one can be generated pretty easily (!KB SEL, IIRC) but one of them cannot.

However the second one is only necessary for a couple of games to work with the FM sound and could be patched.

I've not tried this myself, just going off of memory from the thread.
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  • Joined: 05 Nov 2014
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  • Location: Auckland - NZ
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Post Posted: Wed Jul 01, 2020 5:21 am
I have been looking at this a bit today and it seems like it should work out fine.

The audio inputs on the cart slot feed in through some caps and mix into the psg audio outputs through some resistors. Then its fed over to the audio board.

Im working on some other stuff at the moment and need to build a breakout board for the game gear so ill test this and see how it goes.

The only thing it wont be able to do is switch the psg sound on/off like it does on the jp master system as obviously that sound signal is not fed out through the cart connector. The DB electronics power base fm adapter for the genesis/megadrive will have the same issue. I believe only a few games are effected by that so its probably not a big deal anyway.
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