Is there anyway to get the digital audio signal out of the APU before it is converted into analog? Or is it done internally in the chip with no access to the routing. Be nice to have the option to use a 3rd party DAC.
Thanks
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Philadelphia
captain wrote:
Is there anyway to get the digital audio signal out of the APU before it is converted into analog? Or is it done internally in the chip with no access to the routing. Be nice to have the option to use a 3rd party DAC.
Thanks
I don't know with absolute certainty but I've researched every mod for the NES I could find and never came across this option. If it was possible, someone certainly would have done it by now, so I'm assuming analog RCA out is the best that can be done with the stereo separation pro-sound mod.
Although, there is this:
https://wiki.nesdev.com/w/index.php/APU_Mixer
Not a language I speak but looks like it might be possible?
Last edited by Doctor Octoroc (Feb 17, 2021 6:27 pm)
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Thanks for that. Going to shoot that over to a friend who will understand it a bit more then I can.
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Praha, Czech republic
The 2A0X outputs two analog channels, first is the mix of the two pulse channels and the second is the triangle / noise / DMC. After that, there is the external amplifier, which mixes these two (already analog) signals together. The formula in the link describes the INTERNAL DAC for each of the channels.
To answer your original question, no, there isn't any way to get to the digital representation without decapping the 2A0X. You could do a stereo mod + custom amp by just using the two analog signals directly from the output pins. I've done that personally, the noise floor was about -60 dB.
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Praha, Czech republic
I know your goal is probably using the authentic hardware, but remember, we do live in the age of cycle-accurate emulators 
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kvee wrote:
You could do a stereo mod + custom amp by just using the two analog signals directly from the output pins. I've done that personally, the noise floor was about -60 dB.
Thanks I already considering this as the best option.
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kvee wrote:
I know your goal is probably using the authentic hardware, but remember, we do live in the age of cycle-accurate emulators
Just a semi retired geek with free time do do it the hard way. 
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Praha, Czech republic
captain wrote:
kvee wrote:You could do a stereo mod + custom amp by just using the two analog signals directly from the output pins. I've done that personally, the noise floor was about -60 dB.
Thanks I already considering this as the best option.
All right
It's definitely a worthwhile mod, I had tons of fun even with just these two fixed channels...
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Praha, Czech republic
captain wrote:
kvee wrote:I know your goal is probably using the authentic hardware, but remember, we do live in the age of cycle-accurate emulators
Just a semi retired geek with free time do do it the hard way.
Hey, if you ever DO decap the chip, let me know
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Philadelphia
I'll be following with interest as well! I'm always looking for new ways to push the envelope on the NES, it's by far my favorite sound in its generation.
Also, fwiw, this is the guide I more or less followed to do my mod. I didn't bother with amplification cause it's a good enough signal for my uses but it is really quite simple to do and m soldering skills are next to trash so if I can do it...
http://www.retrofixes.com/2013/09/nes-s … -easy.html
Last edited by Doctor Octoroc (Feb 18, 2021 4:20 am)
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Praha, Czech republic
I'd add a buffer amp still. Look into integrated amp ICs, these come in DIP8 packages and typically require only a few additional components. They typically include the required schematics inside the datasheet as well. As an example, look at TDA2822M (example usage).
When you've got the NES open, I'd also suggest replacing the 1A 7805 regulator with a 3A one if you're gonna do some additional mods (I added LEDs, couldn't resist...). Or better yet, some modern regulator that doesn't produce as much waste heat, but that'd also require some reading into the schematics.
Oh, and I personally disable the CIC chip for stability reasons
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kvee wrote:
I'd add a buffer amp still. Look into integrated amp ICs, these come in DIP8 packages and typically require only a few additional components. They typically include the required schematics inside the datasheet as well. As an example, look at TDA2822M (example usage).
When you've got the NES open, I'd also suggest replacing the 1A 7805 regulator with a 3A one if you're gonna do some additional mods (I added LEDs, couldn't resist...). Or better yet, some modern regulator that doesn't produce as much waste heat, but that'd also require some reading into the schematics.
Oh, and I personally disable the CIC chip for stability reasons
Thanks for that really appreciated I was thinking about a buffer amp. I am looking to any approvement I can make with the sound. Do you know if smoothing the ripple with a shunt regulator in the power supply would also help the sound?.
Last edited by captain (Feb 19, 2021 1:12 pm)
