I just posted this on Assembler but im gonna mirror it here. With links included, this contains all the modding i have done so far on this awesome little GBA-SNES adapter
Sound fixes for the Tototek/gamejoy GBA-SNES AD adapter.Intro and Disclaimer
Using the Tototek AD adapter on a SNES can provide you with the best Possible GBA to TV experience, but the sound it outputs out of the Box is pretty abysmal.
I have devised a collection of fixes to improve audio experience with the GBA-SNES AD adapter. Together these fixes cure pretty much all the sound issues you are likely to encounter when using the AD adapter on your Original SNES.
I am not giving any guarantee of support on those mods, They work here, if they do not work for you or break something I cannot be held responsible. The mods are not guaranteed to be perfect either as I am a hobbyist not a trained electronician. This being said I will try to answer all reasonable questions to the best I can. I tried to keep the fixes as simple as possible so they are easy to do and need as little parts as possible while doing what is intended.
Before we begin please be aware that these fixes have been designed with playing on the SNES in mind. I have good reasons to believe this adapter was designed primarily for clone consoles.
I have not tested the AD adapter on any clone consoles and it might be possible that these fixes are unnecessary on them. (Beside the Stereo sound Fix which a must in any case
Also please note that these fixes have been designed for a V 1.0 GBA to SFC board, future board updates of this GBA adapter might be different.
I do not know yet if this guide will apply to the Super Retro Advance Adapter from Retro bit. I believe it to be the same thing as the AD adapter but this is not known yet.
Before doing any mod on your AD adapter or console please decide how you intend to use it.
A) On a clone console.
B) On a unmodified SNES ( Ad adapter will use the included AV cable )
C) On a SNES modded to use the AD adapter without the cable.
If you want to use it on a clone console, you can do the Stereo Sound mod but I do not know if the other fixes are necessary. You will have to figure that yourself, until I get a clone console.
If you want to use it with its own AV cable on a SNES, most of the modding is beneficial minus the steps designed to make the sound output through the SNES.
If you want to use it on a SNES modded with my No-separate-AV-cable mods, all the fixes will be beneficial. Audio files for comparison.
Before you read through all this thread, consider a little download.
I have made recordings of the original GBA, of the GameCube GB player and of my Modified AD adapter playing through the SNES AV port. I have recorded music from 4 games, so you can compare.
All the audio files are in a single Zip (~140mb) that you can download Here, while you read the rest of the threadl
I will let you decide which one you like the best
Sadly I do not have recordings of the Stock AD adapter, but believe me when I say it is bad. Fix #1: Making the SNES output sound from the Adapter natively.
This mod is done on the SNES and not on the AD adapter. This is an exception as all the other fixes on this page are done on the AD adapter.
If you want to mod your SNES so it is able to output the AD adapter Audio through the regular SNES AV cable, this is how you do it.
Obviously this should only apply to those who wish to do the Cable-less mod where both audio and video from the AD adapter are output through the SNES AV port. For every one else, you can skip right next to fix #2.
The SNES is equipped with all that is needed to output the sound from the AD adapter.
However the SNES has a Mute function that is controlled by a Transistor and it seems muted by default. The designers of the AD adapter did not include in the firmware an instruction to tell the SNES to un-mute the audio. The Idea of the mod is to have the mute function overridden when the AD adapter is connected. When a regular SNES cart is used, the console will behave just as a stock one.
If you want to do this I will assume you also want to do my No-Separate-Cable mod. Here is the complete schematic for the video mod + the Sound through the SNES fix.
You can get all the details for this specific mod there: http://www.assemblergames.com/forums/showthread.php?47904-Modding-the-Snes-so-the-Tototek-GBA-SNES-adapter-does-not-need-separate-AV-cable
The relevant information for this stuff was acquired from the SNES schematics we have available. You need to connect to the Base of a specific transistor labelled Q13 in the Schematics.
Basically the idea is to pull the base of the transistor High by feeding it +5v through a resistor.
It is possible that this "Q13" Transistor might be a different number on different board versions, but the base of it should always be connected with a 33k resistor, and this is the way to find it. On my CPU-GPM-02 this transistor is indeed Q13, but I cannot say for other revisions. Here is a picture of mine but just make sure you have the right transistor for your SNES version.
The orange wire in this picture connects to a Transistor I added in the circuit. You can see it in my AV mod schematic ( the first picture of this chapter) labeled as Q3. You could feed +5v directly without transistor but the idea is for the Mute to be overriden ONLY when the ad adapter is used. When a regular SNES cart is used, the SNES will regain full control over the Mute, just like a stock console. Fix #2: Audio buzz removal.
If you experience a constant and somewhat loud audio buzz with your AD adapter, this will fix it. The buzz is audible as soon as you power the adapter with a game.
This is both the easiest and most worthwhile fix. All you need is a ceramic capacitor. It seems 3nf value is about right but is not critical. IF the value is too high it will glitch the video output. ( I was experiencing glitching at 100 nf). If it is too low likely it will not remove all of the noise.
It should be soldered between R5 and Ground, like on picture below. I though the little unused pad on the right was convenient. R5 is part of the video signal path, and the noise seems to be concentrated at this spot. I have not tried using the cap directly on the Video output, but might work too. Fix #3: Isolating the sound output of the adapter from the SNES/ or separate L and R connector pins. .
If you want to use the AD adapter with its own AV cable on a SNES and will never use it on a clone console, I Highly recommend you do this, just cut that trace and it will completely isolate the sound of the AD adapter from the SNES. Resulting in the AD adapter automatically output significantly louder volume and more bass. This simple trace cut has big impact. However the sound will not work on a clone console that normally does not require a separate cable. If you want to use it on both SNES and Clone console, then you need to go through more steps.
If you want to output the Sound of the adapter through the SNES AV out, this is also one of the first step but there is a twist. What you want in truth is isolate L and R channel pins. They are shorted together with no less than 3 vias ( little hole ) , 2 on the trace and one on the connecter edge itself. A good way to separate the two pins is by twisting an x-acto blade in the vias. You may be able to do this only on the reverse side ( where there is no trace but only vias leading to the pin), which would be ideal. I did not succeed though and ended up cutting the trace while digging the vias on the trace side too. As a result I had to repair it with a little wire.
Once all the vias are severed, you should try to put a dab of solder on the top of the underpin and check with a multimeter that the connection was not "repaired" with the solder. You will need to solder a wire there.
Exemple:Fix #4: Stereo sound
For some reason those who designed the AD adapter decided that Stereo sound was unnecessary. They mixed L and R channels together before the output, despite the fact that the Glob top ASIC is perfectly capable of doing stereo sound.
Have no fear though, we will reverse this affront to all audiophile retro gamers.
Once again, whether you want to use a Modded SNES or not could be relevant. If you are just going to use the separate AV cable and wont mod your SNES, you might be able to get away with less modding. But please read through the whole thing anyway.
Assuming you have done Fix#3, the next step is to cut the trace that shorts L and R at the 1/8 jack.
The stereo sound comes out of the Glob top and goes to two 1.3uf ceramic capacitors labeled C28 and C29. The sound comes on the right side of the Caps and outputs to the left side, where the two signals are joined together.
We will need to remove the caps, so as to separate the two channels. If you want to keep the parts, You can move the two caps to the left pad, like I did in the following picture. This amounts to the same thing as removing them but allows you to keep them in case you ever want to revert the mod.
These caps will be replaced by 100uf electrolytic which is essential for the SNES mod.
However If all you want is stereo sound out of the 1/8 jack and wont be modding you SNES, you do not gain much by replacing the value of these caps beside maybe a tiny bass boost. You can try to take a shortcut and instead of removing them, just move them so they are attached to only the right pad and you would solder wires to the other side of the cap. But I will not go in details with this.
Otherwise we will replace them by 100uf electrolytic caps which is needed to have the sound properly output through the SNES.
The problem is that the SNES also has 1.3 uf caps right at its cartridge sound inputs. So what happens is that two capacitors are in series and they will act as a single capacitor of lesser capacitance.
In this case the Total capacitance is equal to 0,65uf, which is a small value and results in high pass filtering and the sound will be thin and crappy.
The adapter was designed with caps at the output and this helps buffer and protect the Processor from the exterior. Replacing the AD adapter caps with much larger ones will negate the high pass filter effect while keeping a proper buffer on the output. In this Case 100uf @ 6.3V was the largest I could fit inside the adapter case without preventing the thing from closing. It also does the job properly, there is no audible difference with 100uf cap compared to no cap at all.
Now please take note of how things are on the following picture.
The two brown caps are the 100 uf caps and they feed the audio signal to each channel output. Negative side of the cap is on the Output side. ( do not mind the black caps for now, that is fix#5 )
The caps need to be placed on areas where there are no SMD parts underneath otherwise you wont be able to clamshell the adapter case together.
The Right channel output goes through a wire and the cap to connect with the Right channel pin on the 1/8 connector. Unless you completely severed the trace in Fix#3, it will also connect with the Cart connector because there is a trace between them.
For the Left channel, just do the same thing if you do not want to mod your SNES but if you want to mod your SNES you need to do Like in my picture.
The cart connector pin for Left channel should be completely isolated from the Right channel one, because of what we did in Fix#3. Therefore we must connect the sound directly to it, And then from there feed it to the Left channel on the 1/8 jack.
If you have done everything so far, you should have very good sounding stereo sound out of the SNES AV port. Alternatively, if you played the Separate AV cable card and isolated the adapter sound from the SNES, you should have good stereo sound out of the 1/8 AV jack of the adapter.
However there is one more thing to fix..Fix #5: Distortion removal/low pass filter.
There is one last issue that needs to be addressed. In some games, like on metroid fusion, there is a kind of glitch with the adapter. Some sounds will generate high volume "static noises" that distort pretty badly. This seems mostly produced by explosions sounds and it is VERY VERY annoying, to the point of making you worry if its not damaging your speakers.
I have found that lowpass filtering the output with caps to ground can cure this. The more lowpass, the less junk in the audio, but the darker the sound.
Good news is that there is a middle level that has almost no effect on the perceived brightness of the sound while still removing much of the distortion, I would say about 85% of it.
I have found that Using 2.2 uf@35V caps on each output does this. It filters most of the Static noise with minimal impact on the sound "brightness". If you want a more complete removal of static noise at the price of a little more lowpass, which some people might like, use 4.7uf caps instead. And it will sound more like the Gamecube GB player though.
Personally I like bright sound but still, some people might prefer a little more Lowpass since the GBA has a pretty crappy sampling rate or DAC to begin with. It is never going to sound really hi-fi. A little LowPass actually helps to hide some of the DAC artifacts and all the other ugly compression/dithering noises in the GBA audio.
The Game cube adapter has a pretty heavy low pass filter to "censor" all that crap. The original GBA didn't but then you could not hear all the junk through the tiny speaker. But if you played a GBA through headphones, you should know.
The AD adapter has about Zero low pass to begin with so all that high pitched junk goes right through, including the aforementioned static spikes that break your soul as well as your speakers.
I put my 2.2uf caps right on the 1/8 jack output. Like this, ( they may need to be displaced to close the adapter case, I have not tried that yet )
As I said you could always put a slightly higher value for more filtering but honestly I recommend 2.2uF at 35V. If you want to hear how it sounds like with the 2.2uf cap filters, listen to my Samples Conclusion
In conclusion, I would like to say that this adapter exceeded all my hopes and expectations through modding. With all the fixes it performs better in average than all other options including the official product, Gamecube GB player.
There might be some small compatibility issues with a minority of games but the point is that 99% or more of your games will be more enjoyable on a modded AD adapter than on the GC player.
This is obviously my opinion, but I can back it up with facts any time.
This is the reason I bothered to invest this much time in this adapter and why I bothered to write this guide. Because it is totally worth it. This is the best option to play GBA games on your TV with real hardware. Retron 5 is coming soon and might turn out to be superior but it is not "real hardware". And in the meantime AD adapter is the king.Credits
I would like to thank the guys who helped me with the Cable-less video mod by giving me tips and ideas.
I wouild like to thank the guys over at NESDEV forums who helped me figure out the /MUTE circuit on the SNES.
Also a big thanks to the creator(s) of the SNES schematic transcription project. ( source http://forums.nesdev.com/viewtopic.php?p=117691 )
I wont name anyone because I do not want to forget anyone but you guys know who you are!