Gameboy player audio tap points and sound improvement mod.

[Drakon]

Has anyone pointed this out yet? If so please ignore this thread.

*edit* Whoopsies, I just found that there's a modding sub forum, someone please move this thread there.

My buddy ace mentioned the gb player has really muffled audio on the gamecube. I finally noticed the muffle myself so I cracked open the gb player. Thanks to the wonderful nocash documents he mentions the gba cpu pinout which says that the audio lines are pins 6 and 7:

http://nocash.emubase.de/gbatek.htm

The gb player pcb has these convenient "test points" where you can solder wires to the traces and tap the lines:



Sound was clear but had a whining noise. Ace told me a lpf that worked for him so I tried it. Both audio lines have a series 470 ohm resistor followed by a 0.01 uf cap to ground. I built the filter and the sound came out perfect. I wired a toggle switch to go between original system audio and my bypassed audio:



Here's a video where I'm playing music and switching between the audio sources so you can hear the difference:



This muffle may be caused by lpf on the audio lines of the gamecube audio circuit but I can't find any info on the gc audio circuit. It seems like the gb player converts the analog audio into digital and then in the gamecube it converts it back into analog.

[Ashen]

Sexy. I love this kind of stuff from you man! Thanks for sharing.

[Drakon]

Sexy. I love this kind of stuff from you man! Thanks for sharing.

My pleasure. I showed Tiido some of your professional case making in one of your worklogs and it gave him ideas of how to make perfect looking cases for cheaper than 3d printing. Also a big thanks to ace for finding the right lpf for this.

[megalomaniac]

This muffle may be caused by lpf on the audio lines of the gamecube audio circuit but I can't find any info on the gc audio circuit. It seems like the gb player converts the analog audio into digital and then in the gamecube it converts it back into analog.

there is a "translator" IC on the GB player...big chip on the GB player next to the port connector for GC connection
this performs communication between the GC and GB...and i would suspect this is the cause for the issue...
the translator would have to convert the analog audio to digital for the GC to process and then send back out to the AVE.
the AVE only accepts digital input, which it then converts to analog output...

since you can pull the audio from TP 30 / TP31 and with a simple filter circuit added with "perfect" audio, then you have shown the audio is of useful quality before reaching the translator circuit. Unfortunately, bypassing the translator IC at those test points may be the only method possible to achieve this audio mod...
if you wanted to try something, you could cut the trace leading to the translator, then add the LPF circuit inline to the translator to determine if there is any improvement after digital analog conversion by the GC...


ive attached a photo of the audio circuit...
its only 3 digital data lines from the CPU directly to the AVE which then converts them to analog then out to the AV connector...

[Diminuendo]

when I get a hold of mine I'll see if adding your circuit before the analog to digital conversion makes a difference

[Drakon]

Thanks a lot for the schematic megalo. It looks like C129/130 could be low pass filter caps they connect audio lines to what appears to be ground. Perhaps removing those caps will clean up the audio, I'll try it out later. I would do it now but our house is currently going through a Christmas time power outage and I'm at work for internet / heating.

[megalomaniac]

keep in mind, that is an NTSC mainboard...
PAL might be slightly different...
also, there are 2 more caps on the other side of the mainboard...

im not sure if you can just remove them...
i believe the entire circuit is required because the caps require relocation / resoldering when trimming a mainboard for portables...

[Drakon]

Hmm that sounds like a pain. I guess I'll just keep the bypass setup I have instead of risking messing up the circuit unless someone can figure out the strengths of these caps.

[BitFaced]

I can easily perform this myself, right?

[kirjokansi]

Am I missing something here... why is the video's audio starting already bad on the Right channel at the gamecube logo? During the Kirby gameplay and listening only the Left channel, I hear only small difference. But there is a huge difference on the Right channel.

[megalomaniac]

Am I missing something here... why is the video's audio starting already bad on the Right channel at the gamecube logo? During the Kirby gameplay and listening only the Left channel, I hear only small difference. But there is a huge difference on the Right channel.

nice observation, i didnt notice this flaw of the video until i listened with headphones...

video should be considered as invalid data for determining or comparing the results of the modification...
not saying the mod does not work...just saying something is wrong with this video and does not establish a true baseline for comparison...

[Arnold101]

This muffle may be caused by lpf on the audio lines of the gamecube audio circuit but I can't find any info on the gc audio circuit. It seems like the gb player converts the analog audio into digital and then in the gamecube it converts it back into analog.

there is a "translator" IC on the GB player...big chip on the GB player next to the port connector for GC connection
this performs communication between the GC and GB...and i would suspect this is the cause for the issue...
the translator would have to convert the analog audio to digital for the GC to process and then send back out to the AVE.
the AVE only accepts digital input, which it then converts to analog output...

since you can pull the audio from TP 30 / TP31 and with a simple filter circuit added with "perfect" audio, then you have shown the audio is of useful quality before reaching the translator circuit. Unfortunately, bypassing the translator IC at those test points may be the only method possible to achieve this audio mod...
if you wanted to try something, you could cut the trace leading to the translator, then add the LPF circuit inline to the translator to determine if there is any improvement after digital analog conversion by the GC...


ive attached a photo of the audio circuit...
its only 3 digital data lines from the CPU directly to the AVE which then converts them to analog then out to the AV connector...

hello i want to realize this fantastic mod, but i'm in trouble in 2 things: the audio circuit to do is this? (attached)
and where i solder this 2 wires? to the av socket of the GC? but then it will mix up with original game boy player audio. wire it to the expansion connector is not ok since you said this is for digital audio only
please help me thanks a lot

[novenary]

You need to add another connector in the GBP.

[Arnold101]

You need to add another connector in the GBP.

please explain better, a connector with 2 wires that goes to the av socket in the gamecube?

and the schematics i have posted is that correct?

[novenary]

See the first post. The author added a pair of RCA jacks to the back of his GBP and uses these instead of the GameCube audio out.

[Arnold101]

no...the wires you see goes from gbp to av out in the gc, external audio outs are optional, but megalomaniac says that the mod is not confirmed to work since in the video the better audio seems recorded..

[novenary]

No. The wires are the audio from the cube to allow switching between sources without swapping cables.
What Mega was talking about was making the mod on the GC side.

[Arnold101]

ok but seems that this mod is a FAKE!

[iamdablasta]

ok but seems that this mod is a FAKE! :(

Proof? Becuase I can't take your word for it without something seemingly legit to show with your words.

[Arnold101]

ok but seems that this mod is a FAKE!

Proof? Becuase I can't take your word for it without something seemingly legit to show with your words.

read in the first page, the audio seems recorded and lost a channell, i have pm'ed drakon and no answer...

[iamdablasta]

ok but seems that this mod is a FAKE! :(

Proof? Becuase I can't take your word for it without something seemingly legit to show with your words.

read in the first page, the audio seems recorded and lost a channell, i have pm'ed drakon and no answer...

Right, I saw the video after re-reading the thread and something seems off.