Ah. That would work, but personally, I would not favor messing with my $35 EMS cart when I can wire to a DMG which I can replace for half the price given, I do have a few spare DMG's and a busted up EMS cart (no saving, freezes frequently, stuck on bank 2). In a few weeks we can see where this will go.

Oh I wasn't suggesting to use the special pin as output but to use it to signal your internal circuit to switch the internal jack between prosound or regular operation. If you build a momentary toggle switch into a cart (e.g. the EMS cart) that would send 5V down that pin when depressed and you intercept that signal you can use it to toggle your internal switching circuit during runtime without modifying your case.
It's just a wild idea but I don't see a reason that would not work.

Thanks. Considering this is only the second mod I have actually completed (USB MIDI Audio DMG still pending completion) I take this as a big compliment

That pin is for line in, like a microphone or external audio source, not sure if it could do line out (and if it did, it would be mono sound I think). There was talk about building custom carts, etc with special chips. I could see the 5th channel be used with cart that had a 1/8" mono audio jack wired to the pin, and using a patched version of LSDJ to act as a volume-based mixer. Could be nice for using 2xLSDJ or using LSDJ-computer sync with a single patch cable. There could be lots of drawbacks, and I don't see it as an avenue worth exploring past adding native sound enhancements to the Gameboy itself.

Cograts on the double pole double throw switch mod Was talking to kitsch and jazzmarazz about it over the summer, never got around to it. Glad to see it so well executed.

I remember there being that audio input pin in the cartridge connector that almost no cartridge ever used. you could add a push button to your EMS cart and intercept that line, switching between prosound and headphone amp that way with a hardware button and no case mod... (at least no PiL case mod)

Seeing as 2-page carts with bank switching have become the Gameboy standard for changing ROMS, I don't think anyone can complain about rebooting for recording/live/whatever. I'm not sure if people will be fond of soldering 8+ points to the chip (normal audio in L&R, prosound in L&R, audio out, ground, and button detection), but from my idea of visual aesthetics it will be very nice.

My reasoning for this setup is that I am tired of drilling holes in my nice (and not always easy or cheap to come across) Play It Loud cases, I am tired of having to recharge a headphone amp constantly, and I am trying to push myself from a modding standpoint.

Maybe in the future such a thing can be implemented with the still-in-development front PCB replacement? ;D

@thebitman That'd be great! I'll try to keep up with that!

That's a pretty cool idea. Would there be any way to make it switchable after boot or would you have to turn it off and on again if you decide to record something you've been working on on headphones?

I'm working on a designing a simple diagram for a logic gate that will be wired to UP on the Dpad, so if UP is depressed on bootup you get prosound out, and if UP is not pressed on bootup you get standard audio.

I am tired of drilling holes in my pretty DMG shells.

This is a genius idea actually, space effective and just pretty slick all around. I've got one with an internal prosound and it just doesn't give me enough juice when I'm listening in headphones,

I just wanted to report back, that now that I finally have the triwing I've gone ahead and installed a switch next to the A button that switches the source of the built in jack. Up position is pre-pot prosound, down position is headphone amplifier. The difference is really dramatic and very apparent when switching between both settings live. I would have never dreamed to get rid of so much of the hum and hiss with this. Very happy

It was a challenge fitting the switch there, and it was an act of minor force to close the case again, but it works well. The switch doesn't toggle buttery smooth because of a little force that gets applied to it, but it is still switchable easily enough. Everything has been secured with hot glue instead of screws.

I know I could have gone for a separate jack or just hardwired prosound to the internal one, but I had fun figuring this out and I know I couldn't have made a second jack look as clean and almost meant to be there as I was able to do with this switch. Also in the down position everything works just like with an unmodded Game Boy.

yes

I think the double pole portion means each "throw" has two poles, hence the 6 pins I found while searching (2 per throw and 2 output pins) ... so the only logical conclusion I can come up with is that I wire right and left channel for headphones to one throw, right and left channel from prosound to the other throw and the two output pins to the right and left input on the jack ... and when I throw it one way or the other the jack gets either headphone signal or prosound signal.

Is that the same thing you meant? I can't quite tell...

Yeah, the pro-sound / line out audio mod is pretty simple as a concept, but I don't really do "internal" pro-sounds that often, hence my confusion.

A DPDT ("Double Pole, Double Throw") switch has two different positions that connect two different circuits in two different ways. One "pole" would be the left channel, and the other would be the right channel. The switch would control which output is is being sent to the jack; either the line-level output or the normal output.

Or at least that is how I would assume it works, having never tried to mod a Game Boy that way before.

Prosound in the DMG is as far as I've read a straight forward thing, usually connecting R, L and GND of an audio jack directly to three pins next to the potentiometer used for volume control, effectively routing the "pure" sound to said jack.

Reading about DPDT switches it says they have 6 pins, 2 inputs for one side, 2 for the other, and 2 output pins ... so one side would be LR headphones, the other side would be LR directly from the potentiometer and the outputs would go to the jack... will ground be the same for both of them? Are my assumptions correct?

edit: quick explanation of DMG prosound added

Oh, yeah, you're totally right. I'm pretty scatter-brained today, I kept getting hung up on how "destructive" (in my opinion) a typical internal pro-sound is for a CGB.

DMGs are different, and I'll have to admit I don't know as much about the "internal" pro-sound for them.

Could you do this by just  wiring the DPDT between the L and R signal going to the headphone board from the main board, and the L and R signal coming off of the typical pre-pot pro-sound points?