Could pick up something like this. Found it at a vintage gaming store in Taiwan.

Either/both?

I have an SP and I have a headphone adapter, but it's terribly noisy and not suitable for recording or live use.

What exactly are you wanting? Someone to mod your gameboy, or someone to sell you a pre modded gameboy?

Per our convo yesterday, I came here looking for the same thing XD

Could do with another one of these. Is anyone still offering this service?

awesome! thanks

here the old nex pic!

I'm trying to put in a jack myself but the pics on the first page ain't showing so i can't make heads or tails on this i have the pinouts and everything ready to go i just need some theoretical input on where to put the jack. I'm using a jack from the 3DS btw as it is a bit smaller than the one on the pocket and GBC.

From what I read here and seen on your picture I think you should try amplifier pins 7 & 8 for audio. Those labeled LIN & RIN duh

Well I can help you with that.
Don't make fun of how butchered the PCB is, I was experimenting for all our sakes (clicky for large image):

I feel like using these pads is much easier than getting the lines from the EXT2 port where the pads are closer together and soldering is a bitch (I know I tried). In any case all these components are small, so use thin solder, thin cables, patience and a steady pulse.

By the way, this is an AGB-100 motherboard. Perhaps the AGB-101 has a different layout. I don't know. But the pads are clearly marked as FL2 and FR2, so look for that (and the amp) on your circuit board.

You could at least get a breakout headphone plug with this method. The speaker will remain on when you plug this, though, although I was thinking that maybe if you connect the headphone detect pin of the EXT.2 port to either L or R on the minijack plug you add, it could work shorting it to ground when a headphone is connected (anyone with a lot more experience in electronics than me, can correct me because I probably am saying nonsense).

In any case, as I said, this is not a pro-sound mod, I couldn't skip the amp (if this skips it, I didn't notice it, didn't seem loud enough to me) and the volume pot is still connected to whatever plug you put there.

Waiting for NeX's pictures, to be honest. I spent all this afternoon fighting with this GBA SP.

I, too, am curious - not only for noise reduction, but also mainly because i'm sick of buying GBASP headphone adapters.  i've gone through 3 of them already and i don't have nimble enough chops to fix 'em.

I've also been curious. I've seen other guides on adding a jack but not prosounding it. Sp adapters are in short supply nowadays so I might be doing this to all of mine.

Well all the pics are gone thanks to them being hosted at 8bitcollective.
Anybody saved a copy of the photos of the procedure to get a GBA SP prosounded?
I been fiddling around and I found points in the motherboard where I can get a decent output (they are kinda clearly labeled around the amp circuit), but it's still tied to the pot so I assume it's not prosounded. It doesn't sound very loud either.

I also have no clue how you could fit a 3.5" minijack in there, even less an arduino, so I'd love to see NEX's original pictures.

I don't know how much you know about this stuff Trash80, but please don't take it as an insult if i go into detail, its more for the benifit of others. the SP has a single cap, and it is there to create an AC voltage. the SP doesn't create a negative voltage, so it creates a mid way point using a cap. the bigger the cap the better bass response in theory. the DMG has two caps, one on the left channel and one on the right, they are down on the small board on the headphone jack, again they are there to create a mid point so the voltage can go to a virtual minus. but this is not what you want for a line level recording, as you want the raw DC output. the caps on gameboys can be cheap and old and effect the sound. but in this case of the pro sound SP the cap is still in place on the other side.

but this is only for the SPs with the older amplifier, the more modern AGS101 boards give a very nice and clear sound when pro sounded, very close to what the DMG can do, except with the sp slightly distorting wave sounds which is a problem with the CPU itself.

do you want to drop me a mail? ralph (dot) nex (at) gmail (dot) com