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View topic - Anyone ever put FM sound into a game gear? I'm planning to try, looking for tips

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  • Joined: 22 Feb 2016
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Anyone ever put FM sound into a game gear? I'm planning to try, looking for tips
Post Posted: Thu Jan 14, 2021 3:27 am
Finally getting around to planning a game gear build, hoping to do the consolized thing to make it functional for SMS on a TV too. The last couple things I'm looking into are an FM mod, and maybe eventually some info on the LCD glasses adapter.

I think I have the wiring and schematics all figured out for modifying an SMSFM unit, but I guess I was just hoping to talk to someone who might have done this mod before, with the SMSFM unit or without. I'm not even sure I have specific questions at this point, but I'm committed to give it a try at least and will probably update here with any progress when I finally attempt it.

I can find hints of people trying it, a message from "viletim" himself saying he had wired one of his SMSFM unit into a game gear just to test it eleven years ago, other messages on various forums of people asking for advice, but no messages/pictures/videos of finished projects.

Wiring the module into the game gear seems pretty straight forward but with a few considerations (not mentioning the space needed to fit it in there).

First, the game gear apparently doesn't have a "joykill" pin, so two games won't work without patches.

Second, the game gear is stereo and the SMSFM module is designed to mix in and pass through mono sound. I could just settle for mono sound, there's really only a handful of game gear games that utilize it well, but I think I've managed to copy down the mixing part of viletim's SMSFM board so I can hopefully add a few components to it and make it stereo. This stuff is right at the edge of my knowledge and skills though, so we'll see.

Third is exactly WHERE to mix in the FM sound. using the guide for generic SMS consoles, I followed the audio schematic and found caps that I think is where I would mix it in, on the audio board, caps C5 and C7. Although comparing to an SMS console, I wonder if before the audio board wouldn't be better, it would be easier to keep everything on the main board.

Anyway, I appreciate any advice anyone has and regardless I'll be sure to update if I manage to get things working. Thanks!
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  • Joined: 05 Sep 2013
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Post Posted: Thu Jan 14, 2021 5:40 pm
I don't know how you mix the FM and PSG part but I would send the FM to both audio channels and leave the PSG as stereo instead of mixing PSG into mono...

but, again, I have no idea what this requires
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  • Joined: 22 Feb 2016
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Post Posted: Thu Jan 14, 2021 9:45 pm
I could just wire it mono, which would be super easy, but like you said I'm trying to keep psg stereo while adding fm sound. The issue is that the smsfm was designed for mono sound. To get the mixing circuit working right, I have to basically double that part so one mixes FM into the right channel and one mixes it into the left.

I also posted this question in other sites and someone directed me to a page here titled "Game Gear Cartridge FM Audio?" By bsittler back in may. Last activity was around December so it's pretty recent. Don't know why I couldn't find it...

Not built into a gg, and it doesn't use the mixing circuit, but this at least confirms to me that it works like I thought it would and also tells me where to add it into the circuit.
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