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 Post subject: SNES digital audio dropouts solution
PostPosted: Mon Mar 11, 2019 4:16 am 


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I just finished listening to RetroRGB's latest Q&A video and at around 19:30 a person brings up audio dropouts they're experiencing with borti's digital audio board.

At one point I had 8 consoles modded with borti's 32khz digital audio boards, 4 Mini's and 4 fat 1CHIP's. Some were toslink and some were coaxial, each using a DIT4096. When testing out on my receiver, a Yamaha RX-V477, all 4 1CHIP's worked perfectly fine with no dropouts at all. When testing out the Mini's, all 4 had an obnoxious amount of audio dropouts. I took a short video at the time to showcase the issue. I didn't get any audio dropouts with a cheap PROZOR DAC but with this receiver it was awful. I had followed the installation method shown on RetroRGB's site since it was easier to use those vias rather than solder directly to the S-APU pins. Some pics of one install:

Image
Image

Despite having a clean install, the dropouts randomly occurred every 3-20 seconds or so. Why were the 1CHIP's working without issue but Mini's having dropouts? I couldn't for the life of me figure out why this was happening given that my installations were clean along with the fact that Mini's and 1CHIP's are essentially identical consoles. I reached out to L-Train for help. He suggested the variance in compatibility might have to do with the difference in location of the S-APU between each console. On Mini's the S-APU is located near the front of the console and on 1CHIP's it's located at the back. With Mini's, most people will grab the digital lines from the vias and route them to the back of the console. When doing so, the digital input lines are too long and become compromised. This isn't an issue on 1CHIP's since the S-APU is located near the back of the console hence the digital input lines aren't nearly as long. Because of this he suggested that I try mounting the digital audio boards of the Mini's closer to the S-APU and wiring the output to the back of the console instead, which I did:

Image

In one console I mounted the board directly on top of the S-APU as I wanted the digital input lines to be as short as possible. I hooked it up to my receiver for testing and I went 2 hours without a single audio dropout. I then redid the other 3 Mini's and tested those consoles 2 hours each. In total 8 hours of play and not a single audio dropout. At this point I was confident in saying that mounting the board closer to the S-APU completely solved the audio dropout issue. All hail L-Train.

This isn't a callout or personal attack by any means, as I'm simply trying to help people who might be experiencing compatibility issues, but the digital audio installation method for SNES Mini's shown on RetroRGB's site, in my experience, will yield suboptimal results. The digital input lines are too long and become compromised. I suspect that most cases of users experiencing compatibility issues has actually nothing to do with the quirky sample rate of the SNES but rather compromised digital input lines. What also came to mind was this has been the go-to method for digital audio installs in SNES Mini's for some time now so that can only mean there are many Mini's out there with improperly installed digital audio mods. I can't guarantee that this method (mounting the board closer to the S-APU) will resolve all compatibility issues as I haven't tested every DAC in the world but it certainly fixed mine. In fact, with this method, every 32 khz compatible DAC that I've tried has worked flawlessly, including:

-Monolith by Monoprice Desktop Headphone Amplifier and DAC
-Monolith by Monoprice Portable Headphone Amplifier and DAC
-Topping DX3 Pro
-SMSL SU-8
-Parasound Zdac v.2 DAC and Amp
-PROZOR DAC
-Yamaha RX-V477

With regards to my Topping DX3 Pro, it is listed as supporting 44.1 to 192khz only, yet it works fine with borti's 32khz board when I turn off the Auto-Off feature. On a sidenote, the Topping DX3 Pro is one of the best bang for your bucks in audiophilia at the moment, for those that dare to go down that rabbit hole, although I recommend waiting for the revised unit that should soon be out.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Mon Mar 11, 2019 5:42 am 


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Weird. I don't get dropouts on my rear installed mini, though I use my own board with the CS8406, and I use 26AWG multi-strand ribbon wire instead of kynar. Not sure if either one of these makes a difference, but I can appreciate the idea of mounting the board directly on the chip. It would mean using a longer data line to the output jack in the rear, but I'm guessing that's a more robust signal.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Mon Mar 11, 2019 4:48 pm 



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Excellent work unmaker! Good to know that this solves your dropouts. I've got a new "universal" SPDIF transmitter board I've designed using the DIT4096 and am planning to install it in my Mini for testing, so now I know to install it as close to the S-APU as possible for best results.


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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Tue Mar 12, 2019 3:52 am 


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FBX wrote:
Weird. I don't get dropouts on my rear installed mini, though I use my own board with the CS8406, and I use 26AWG multi-strand ribbon wire instead of kynar. Not sure if either one of these makes a difference, but I can appreciate the idea of mounting the board directly on the chip. It would mean using a longer data line to the output jack in the rear, but I'm guessing that's a more robust signal.


I initially had these installed with kynar wire. Thinking that might be the problem, I swapped it out for 26awg single-stranded wire shown in the first post. That didn't seem to make any difference, the audio dropouts continued. At this point I was clueless and reached out to L-Train. I'm thinking you could also mount the PCB on the bottom side of the console between the vias instead of directly on top of the S-APU. That should work fine and it'll be easier that soldering directly to pins 94,93, and 92. This will also reduce the length of the output lines but so far I haven't had any trouble with the current length.

I have in the past installed borti's CS8406 board but I did not have this receiver at the time so I wasn't able to test it out for dropouts. I'm curious if there's any difference in dropouts between it and the DIT4096. It seems he removed this design from his OSHpark page when he released his DIT4096 toslink and coaxial designs.

L-Train wrote:
Excellent work unmaker! Good to know that this solves your dropouts. I've got a new "universal" SPDIF transmitter board I've designed using the DIT4096 and am planning to install it in my Mini for testing, so now I know to install it as close to the S-APU as possible for best results.


Thank you L-Train! You've been a tremendous help several times already. I'm excited to hear that you've got a new design in the works! Other than using a DIT4096, how will your new SPDIF board differ from your current? Big fan of your current board. I've got one installed in my N64 after I saw your post where you installed one in yours. I'm considering making a tutorial for the N64 since I don't think many people are aware that you can do this. The installation also differs between console revisions since not all consoles have a BU9480F DAC.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Tue Mar 12, 2019 6:49 am 



Joined: 11 Jun 2014
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unmaker wrote:
I'm excited to hear that you've got a new design in the works! Other than using a DIT4096, how will your new SPDIF board differ from your current?

It's a straight SPDIF transmitter with no resampling just like many of the DIT4096 boards out there, but with jumpers to configure the clock and format pins. This should make it compatible with the SNES, PlayStation, Saturn, Dreamcast, etc. It's also on a 4 layer board which allows it to be pretty small (1.1" x 0.775") with good routing and bypassing. There was even room to add a small XOR gate and jumper to select between active-high and active-low pre-emphasis. Not that anyone listens to CDs with pre-emphasis anymore, but I noticed some systems provide a pre-emphasis signal so it's there for completeness.

The pads for the VIO and VDD supplies are also separate in case the logic level of the source differs from the 5V required to power VDD. I believe the Dreamcast is 3.3V, and perhaps maybe the PlayStation is as well? That's something I need to look at when I get my hands on one.

unmaker wrote:
I've got one installed in my N64 after I saw your post where you installed one in yours. I'm considering making a tutorial for the N64 since I don't think many people are aware that you can do this.

Cool! Have you found any incompatibilities or experienced any strange behaviour with it so far? I think a tutorial would be a great resource for those interested in the mod.

As an aside, I've recently been looking to purchase a Neo Geo MV-1C to consolize and read that it uses a BU9480F just like the N64, so it's possible my board will work with it as well. Luckily since my board resamples to 96 kHz it preserves the full bandwidth of the ~55.5/55.6 kHz digital audio signal the YSA2 produces.


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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Tue Mar 12, 2019 9:41 am 


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L-Train wrote:

As an aside, I've recently been looking to purchase a Neo Geo MV-1C to consolize and read that it uses a BU9480F just like the N64, so it's possible my board will work with it as well. Luckily since my board resamples to 96 kHz it preserves the full bandwidth of the ~55.5/55.6 kHz digital audio signal the YSA2 produces.


Funny you should mention that. I just got an MV-1C to start working on a digital audio mod myself. Some people were worried about an analogue SSG channel being missing, but my research in mapping out the Neo-YSA2 chip suggests that the ASIC YM chip is 100% digital output, including the SSG channel.

BTW on your OSH Park board listing, you don't need the extra via to the side. The OSH Park warning is something that you can simply check off as 'correct' and the boards are produced just fine. Several of my boards don't have a bottom solder mask stop either, and I just check off that warning and send it off for fabrication as-is.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Tue Mar 12, 2019 2:34 pm 



Joined: 11 Jun 2014
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FBX wrote:
Some people were worried about an analogue SSG channel being missing, but my research in mapping out the Neo-YSA2 chip suggests that the ASIC YM chip is 100% digital output, including the SSG channel.

Awesome! Thanks for taking the time to verify that its audio is fully digital.

FBX wrote:
BTW on your OSH Park board listing, you don't need the extra via to the side. The OSH Park warning is something that you can simply check off as 'correct' and the boards are produced just fine. Several of my boards don't have a bottom solder mask stop either, and I just check off that warning and send it off for fabrication as-is.

Back in 2015 when I uploaded this board, OSH Park didn't have that functionality and gave an error which actually prevented you from continuing to the preview. An OSH Park employee suggested putting a via outside of the board area to give the bottom side some solder mask "negative", and the workaround worked. Thankfully it doesn't increase the cost of the board so I've left it as-is.


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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Tue Mar 12, 2019 4:32 pm 


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L-Train wrote:
Back in 2015 when I uploaded this board, OSH Park didn't have that functionality and gave an error which actually prevented you from continuing to the preview. An OSH Park employee suggested putting a via outside of the board area to give the bottom side some solder mask "negative", and the workaround worked. Thankfully it doesn't increase the cost of the board so I've left it as-is.


Ah interesting! So they didn't have the check clear option back then. They do now, so it's just a simple "by the way, you don't have a bottom solder mask stop" warning instead of a critical "we can't make this" error.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Wed Mar 13, 2019 3:41 am 


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L-Train wrote:
unmaker wrote:
I'm excited to hear that you've got a new design in the works! Other than using a DIT4096, how will your new SPDIF board differ from your current?

It's a straight SPDIF transmitter with no resampling just like many of the DIT4096 boards out there, but with jumpers to configure the clock and format pins. This should make it compatible with the SNES, PlayStation, Saturn, Dreamcast, etc. It's also on a 4 layer board which allows it to be pretty small (1.1" x 0.775") with good routing and bypassing. There was even room to add a small XOR gate and jumper to select between active-high and active-low pre-emphasis. Not that anyone listens to CDs with pre-emphasis anymore, but I noticed some systems provide a pre-emphasis signal so it's there for completeness.

The pads for the VIO and VDD supplies are also separate in case the logic level of the source differs from the 5V required to power VDD. I believe the Dreamcast is 3.3V, and perhaps maybe the PlayStation is as well? That's something I need to look at when I get my hands on one.


Man, where were you and your board when I installed SPDIF on all of the consoles you mentioned years ago? :lol:
Would have made life so much easier...


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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Thu Mar 14, 2019 11:40 am 


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L-Train wrote:
It's a straight SPDIF transmitter with no resampling just like many of the DIT4096 boards out there, but with jumpers to configure the clock and format pins. This should make it compatible with the SNES, PlayStation, Saturn, Dreamcast, etc. It's also on a 4 layer board which allows it to be pretty small (1.1" x 0.775") with good routing and bypassing. There was even room to add a small XOR gate and jumper to select between active-high and active-low pre-emphasis. Not that anyone listens to CDs with pre-emphasis anymore, but I noticed some systems provide a pre-emphasis signal so it's there for completeness.

The pads for the VIO and VDD supplies are also separate in case the logic level of the source differs from the 5V required to power VDD. I believe the Dreamcast is 3.3V, and perhaps maybe the PlayStation is as well? That's something I need to look at when I get my hands on one.


That's awesome! I've been meaning to mod myself a Playstation with a PSIO and SPDIF output. I just haven't gotten around to yet it. I had citrus3000psi's toslink mod in mind but now that you've got a design coming out I'd rather try yours when I finally get around to it. Admittedly I'm not too familiar with some of the terminology you use here (active-high,active-low) but I'd still love to give your board a shot.

L-Train wrote:
Cool! Have you found any incompatibilities or experienced any strange behaviour with it so far? I think a tutorial would be a great resource for those interested in the mod.

As an aside, I've recently been looking to purchase a Neo Geo MV-1C to consolize and read that it uses a BU9480F just like the N64, so it's possible my board will work with it as well. Luckily since my board resamples to 96 kHz it preserves the full bandwidth of the ~55.5/55.6 kHz digital audio signal the YSA2 produces.


So far I have not run into any issues at all with the N64 but I haven't used it a whole lot since the SPDIF mod. Somewhere around 1.5 to 2 hours total. I've played a dozen or so games with my Everdrive 64 in that time and no incompatibilities thus far. If I ever run into any issues with it in the future I'll definitely let you know.
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Thu Mar 14, 2019 8:58 pm 


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unmaker wrote:

That's awesome! I've been meaning to mod myself a Playstation with a PSIO and SPDIF output. I just haven't gotten around to yet it. I had citrus3000psi's toslink mod in mind but now that you've got a design coming out I'd rather try yours when I finally get around to it. Admittedly I'm not too familiar with some of the terminology you use here (active-high,active-low) but I'd still love to give your board a shot.


I've done Dan's Toshiba-based mod on the Playstation and it works great. I wrote an article about it here:

http://www.firebrandx.com/psxdigitalaudio.html

-FBX
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 Post subject: Re: SNES digital audio dropouts solution
PostPosted: Sat Mar 16, 2019 4:28 am 


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FBX wrote:
unmaker wrote:

That's awesome! I've been meaning to mod myself a Playstation with a PSIO and SPDIF output. I just haven't gotten around to yet it. I had citrus3000psi's toslink mod in mind but now that you've got a design coming out I'd rather try yours when I finally get around to it. Admittedly I'm not too familiar with some of the terminology you use here (active-high,active-low) but I'd still love to give your board a shot.


I've done Dan's Toshiba-based mod on the Playstation and it works great. I wrote an article about it here:

http://www.firebrandx.com/psxdigitalaudio.html

-FBX


I've been aware of Dan's mod for some time now but just sort of lost interest in it. When I saw you post this article on twitter it definitely revived my interest, along with the availability of the PSIO.
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