Digital audio sample rate converter: S/PDIF for N64, MV1C

[L-Train]

Thanks for including the BOM. I see the CS8406 your, FirebrandX's mod and older version of borti4938's mod still for sale was obsoleted with an end of life notice 12 months ago. Not surprisingly of stock.

Last year's EOL was for the SOIC version of the CS8406 and I thought we'd be safe with the TSSOP version used in my mod, but unfortunately the day after your reply Cirrus Logic EOL'd the TSSOP version as well. If anyone's planning on building one of these things please place your orders for the CS8406 while they're still available. I plan on redesigning the board to use the DIT4192.

I assume the [more expensive] $10-12 USD CS8416-CZZ is the intended replacement.

The CS8416 is a digital audio receiver and isn't suitable for this application.

--Can you measure the power consumed and ambient operating temperature at the highest resample rate or is that not meaningful?

This is something I was meaning to measure but forgot to do it. Thanks for reminding me! The next time I have one on the bench I'll try to remember to do this.

--Is the mod in standby mode or something akin to that when Super Game Boy or MSU-1 audio is running?

No, there's no standby mode and it continuously resamples and outputs whatever is produced by the APU.

--Can you confirm if 1CHIP has inferior audio to 2CHIP? I'll test this myself but I'm biased in thinking 1CHIPs are cheap cost reduction machines with the SNES Jr/Mini being almost a clone console. Important distinction when 2CHIP digital mods are much more difficult.

plgDavid has done extensive measurements and his video about the research behind chipsynth SFC indicates that the digital audio they produce is practically identical. I did a quick check too, just a simple inversion test with a regular SNES with a DIT4192 and a SNES Jr. with a CS8406. Due to the differences in state at boot (explained starting at 10:42 in the video) the cancellation isn't perfect, but there are sounds that are cancelled completely which implies that they can be bit perfect.

--Can I ask what we refer to in American English as the 800-pound gorilla in the room question? At sub-CD audio with arguably high noise floor, which is to say SNES and N64, is the digital reduction in noise significant enough to make any audible difference? I was discussing that with Ikaruga11 and I predicted definitely not for 3.56:1 audio compression ratio, expected 32 kHz DAC SNES. Maybe yes for N64 from the rare game coded to use 44 kHz sampling. By extension, I think going up to 24-bit, 192 kHz sampling, 24 Mbps is silly but not going to hurt anything.

By digital reduction in noise do you mean the difference between the analog audio produced by the NEC DAC inside the console versus a pure digital signal? If so, the most audible differences are the elimination of 50/60 Hz hum and 15.7 kHz interference, and the lack of low pass filtering. A lower noise floor can be audible when using a high quality DAC, but is less noticeable. If you're asking about a potential reduction in noise from the 24-bit output of my mod, no, the noise floor is limited by the 16-bit PCM samples from these consoles.

My apologies for the lateness of my reply!

[NewSchoolBoxer]

--Can you confirm if 1CHIP has inferior audio to 2CHIP? I'll test this myself but I'm biased in thinking 1CHIPs are cheap cost reduction machines with the SNES Jr/Mini being almost a clone console. Important distinction when 2CHIP digital mods are much more difficult.

plgDavid has done extensive measurements and his video about the research behind chipsynth SFC indicates that the digital audio they produce is practically identical. I did a quick check too, just a simple inversion test with a regular SNES with a DIT4192 and a SNES Jr. with a CS8406. Due to the differences in state at boot (explained starting at 10:42 in the video) the cancellation isn't perfect, but there are sounds that are cancelled completely which implies that they can be bit perfect.

Really interesting video, thanks for showing me. You've already tested DIT4192, that's great! I was thinking of audio going out of the analog ports being worse. I can imagine 1CHIP/Jr. being extremely similar or nearly identical from the digital sampling stage, barring some known audio glitches.

I 100% agree with video about prioritizing the first model's audio that was the most widely produced. Video was cringe on the science end. Selling the synthesizer with the claim the SNES model revisions all sound the same makes his work much easier. plgDavid states the wrong cutoff frequency for the preamp, which looks pretty bad. The sim.okawa-denshi.jp site I use too doesn't give the cutoff here. I believe the transfer function is correct from cascading the passive RC and active Sallen-Key 2nd order RC. Can find cutoff on WolframAlpha by:

Spoiler

enter: magnitude of 5.2174638951498E+14/(s3+141414.14141414s2+14921946740.129s+5.2174638951498E+14) where s=2*pi*11624*i
copy answer and set equal to sqrt(2)/2 for -3 dB point: sqrt(2)/2=(5.2174638951498×10^14)/abs(-248.05021344240 i w^3 - 5.582806529909×10^6 w^2 + 9.375735651209×10^10 i w + 5.2174638951498×10^14)
answer: w≈11623.921139745785 = 11.624 kHz

11.624 kHz cutoff to drop ~30% of voltage level is extreme. I like your reasoning of a filter wanting to suppress 15.7 kHz noise that implies a very low cutoff but this can't hit 50/60 Hz hum. I simulated the preamp filter and got the same 3 dB point:

Spoiler

(click for full size)

LM324 preamp filter: Q factor of 1/(2*zeta) = 1.118 > 1 is pretty wonky when 3rd order Butterworth filter has Q of 1.000 on the opamp and Bessel of 0.691, with some tolerance for non-exact R and C values. Playing around in Micro-Cap 12 and Analog's Filter Wizard and comparing group delay, I'm fairly confident Nintendo went for a 2/3 Butterworth 1/3 Bessel hybrid filter. Is a legit design strat but forcing matching resistors versus letting R3 be 10x greater messes up the damping that reduces the passband. Lowering manufacturing costs by reusing same resistor value must have been more important.

The video's audio measurements are lacking when they only show MDFourier. I don't expect team with niche market to have a MATLAB or Adobe Audition license but affordable digital oscilloscopes have built-in THD+Noise and FFT and can easily measure channel separation.

He's giving himself an unfair advantage by recording digital capture from box from his own APU that sits outside the console to cut electromagnetic interference and avoid the unfiltered power supply. Compares this hyper clean audio with his own software tuned to match it, then against accurate emulators that would have used real console samples. In theory, they emulated the filter and other analog circuitry that plgDavid is skipping. He could reassure me with analog capture comparisons.

--Can I ask what we refer to in American English as the 800-pound gorilla in the room question? At sub-CD audio with arguably high noise floor, which is to say SNES and N64, is the digital reduction in noise significant enough to make any audible difference? I was discussing that with Ikaruga11 and I predicted definitely not for 3.56:1 audio compression ratio, expected 32 kHz DAC SNES. Maybe yes for N64 from the rare game coded to use 44 kHz sampling. By extension, I think going up to 24-bit, 192 kHz sampling, 24 Mbps is silly but not going to hurt anything.

By digital reduction in noise do you mean the difference between the analog audio produced by the NEC DAC inside the console versus a pure digital signal? If so, the most audible differences are the elimination of 50/60 Hz hum and 15.7 kHz interference, and the lack of low pass filtering. A lower noise floor can be audible when using a high quality DAC, but is less noticeable. If you're asking about a potential reduction in noise from the 24-bit output of my mod, no, the noise floor is limited by the 16-bit PCM samples from these consoles.

My apologies for the lateness of my reply!

It's fine, I disappeared for a few months. Great and helpful responses! Was what I was asking, how much better, however 'better' is defined, is pulling digital audio directly from the chip going to sound versus going through the SNES DAC + filter? Noise floor limited by console sampling bit-compressed data makes sense. Can sound better in the sense of not using an ancient DAC and arguably poorly designed filter with ancient LM324 amp. The 15.7 kHz horizontal sync interference, I wouldn't have thought of that but seems obvious now.

I guess there's two ways to do this: extract digital audio that can sound better/cleaner or record the analog audio that can sound worse/accurate. I have the prosumer recording equipment for the latter to see if 1CHIP RCA audio is same or worse than earlier revisions. Limitation is having one 1CHIP.

[GK6475]

Anybody here in 2024? I can't get my board to work for some reason, and I've checked everything for continuity multiple times, including the wires to the N64's motherboard. My amplifier shows that it is getting a signal, but no sound plays through it at all, and I know that this amp works in the way that I have it set up. I'm really not sure what's wrong at this point, and I've tried both the coax and optical outputs from the board, and I have tried using 470 ohm resistors inline with the RCP's output. I would post images if I knew how.

[L-Train]

Anybody here in 2024? I can't get my board to work for some reason, and I've checked everything for continuity multiple times, including the wires to the N64's motherboard. My amplifier shows that it is getting a signal, but no sound plays through it at all, and I know that this amp works in the way that I have it set up. I'm really not sure what's wrong at this point, and I've tried both the coax and optical outputs from the board, and I have tried using 470 ohm resistors inline with the RCP's output. I would post images if I knew how.

Hi, do you have close up pictures of your build and install? Edit: I somehow missed your last sentence lol. You can create an account and upload images to imgur.com, then link to them here via the image URL.

[GK6475]

Anybody here in 2024? I can't get my board to work for some reason, and I've checked everything for continuity multiple times, including the wires to the N64's motherboard. My amplifier shows that it is getting a signal, but no sound plays through it at all, and I know that this amp works in the way that I have it set up. I'm really not sure what's wrong at this point, and I've tried both the coax and optical outputs from the board, and I have tried using 470 ohm resistors inline with the RCP's output. I would post images if I knew how.

Hi, do you have close up pictures of your build and install? Edit: I somehow missed your last sentence lol. You can create an account and upload images to imgur.com, then link to them here via the image URL.

Here:
https://imgur.com/a/gjqLsPx
The image at the bottom should be the newest and clearest image that I have of the mod. I made absolutely certain that all of the input wires are connected where they need to be, and tested continuity for them as well.

[L-Train]

Here:
https://imgur.com/a/gjqLsPx
The image at the bottom should be the newest and clearest image that I have of the mod. I made absolutely certain that all of the input wires are connected where they need to be, and tested continuity for them as well.

Thanks. Since your amplifier is getting a signal there's likely no issue with the CS8406's clocking or output, which steers us toward the input buffer of the board. I can't see any immediate shorts from the pictures you provided, but here's an image of the layout:



You've checked for continuity to ensure things are connected, but have you checked for shorts? If not, check for shorts between all adjacent pins on IC2 (i.e. 3.3V and N$4, N$4 and GND, etc.). The input and output pins of the buffer should not be shorted to 3.3V, GND, or to each other.

[GK6475]

Well, I had tried rebuilding the board onto a different PCB, given that the old one looked a bit rough, and now I’m not getting any indication of a signal on my receiver. The last photo in the link is of the rebuilt board. I’ll have to play around with it tomorrow and see if I can fix that issue. Funny that the old one was working better than the new one, given how much rougher it looked.

Edit: So, if the output doesn't show up on my reciever, could the SRC192 be part of the cause? Or is that exclusive to the CS8406?

Edit2: nothing appears to be shorted, but my multimeter reads that 3.3v and ground are shorted, but only when the N64 is powered on. I've swapped out all of the capacitors and such, and I've checked every little pin for any visible shorting, but couldn't find any. I've been reflowing this thing for hours and I have no idea where to go with this at this point.

[GK6475]

I think that one of the main issues is that I don't have the proper equipment for SMD soldering like this. The pins are shorting beneath the chips, it seems. Woild I be able to have you build a board for me? I could cover any costs, of course. I could send you the components if needed. I just really want to have digital audio from my N64 and I just can't seem to get the soldering to work out.

[L-Train]

I think completing the board brings you 95% of the way there, we just need to put in that last 5% of troubleshooting.

If there are no shorts between 3.3V and GND when the board is unpowered then it should be okay. Continuity shouldn't be tested between 3.3V and GND while the board is powered. What voltage are you reading at the output of the 3.3V regulator?

No valid signal at the output of the CS8406 may be due to either the CS8406 or the SRC4192. With the board powered (and first verifying that the 3.3V regulator is outputting 3.3V), here are some things you want to check:

1. Check that the input /RST signal coming from the N64 is high (i.e. 3.3V)
2. Check that buffered reset signal on IC2 (pin 6, net N$15 in the image I had attached) is also high. If it's low (0V) then the SRC4192 and CS8406 are being held in reset and won't output anything.
3. Check that pin 1 (denoted by the dot/circle) on the clock oscillator is high
4. Check the coaxial output wires for shorts to the adjacent optical output pads or GND. I see some stray bits of shielding in the images you've given that may be shorting to something. For testing, instead of the shielded cable you can just use two reasonably short wires connected the center and shield conductors of an RCA jack.

When you're reflowing your joints are you using additional flux to aid in wetting? If not, I recommend something like an MG Chemicals 835-P flux pen. You should also clean the board with 99% isopropyl alcohol, a toothbrush, Q-tips, and paper towel for absorbing the broken down flux residue. The paper towel is key, a toothbrush alone will only move the flux residue around the board.

[GK6475]

I think completing the board brings you 95% of the way there, we just need to put in that last 5% of troubleshooting.

If there are no shorts between 3.3V and GND when the board is unpowered then it should be okay. Continuity shouldn't be tested between 3.3V and GND while the board is powered. What voltage are you reading at the output of the 3.3V regulator?

No valid signal at the output of the CS8406 may be due to either the CS8406 or the SRC4192. With the board powered (and first verifying that the 3.3V regulator is outputting 3.3V), here are some things you want to check:

1. Check that the input /RST signal coming from the N64 is high (i.e. 3.3V)
2. Check that buffered reset signal on IC2 (pin 6, net N$15 in the image I had attached) is also high. If it's low (0V) then the SRC4192 and CS8406 are being held in reset and won't output anything.
3. Check that pin 1 (denoted by the dot/circle) on the clock oscillator is high
4. Check the coaxial output wires for shorts to the adjacent optical output pads or GND. I see some stray bits of shielding in the images you've given that may be shorting to something. For testing, instead of the shielded cable you can just use two reasonably short wires connected the center and shield conductors of an RCA jack.

When you're reflowing your joints are you using additional flux to aid in wetting? If not, I recommend something like an MG Chemicals 835-P flux pen. You should also clean the board with 99% isopropyl alcohol, a toothbrush, Q-tips, and paper towel for absorbing the broken down flux residue. The paper towel is key, a toothbrush alone will only move the flux residue around the board.

Ok, thanks, I'll try to get it working with this info, but I also decided to order some new SRC4192 chips as well to see if that helps, so it may be a bit before I reply again (the order will probably arrive in 2 weeks, as it was the cheapest way to get the chips).

[GK6475]

So, I tried to get either of my boards working for a few hours today and they still don't work. I did get my SRC4192 chips early. One of them doesn't send any signals to my reciever, and the other shows up on my reciever but no audio will play. I've tested for continuity and between pins for the audio input through the LC86A and to the SRC4192, for the one that sends a signal. I imagine my best bet is with the board that at least sends a signal, but I still can't get that one working. Also, is it normal for 5v and ground to show as shorted by my multimeter when everything is hooked up, but the console is off? They are not shorted when I remove the board from the N64. I did make sure that my ground point is the big metal spot on the side of the regulator, like your photo.

Edit: after trying to refine the board that outputs a blank signal, it now outputs nothing. I am at such a loss with all of this. I've never had this much trouble with building an SMD-based board before. I really just need someone to build one for me at this point.

[L-Train]

A short between 5V and ground when everything is hooked up but unpowered is not normal.

When you say that 5V and ground are not shorted when you remove the board from the N64, do you mean between 5V and ground on the board, or between 5V and ground on the N64? If you only checked the board, also check between 5V and ground on the N64. If there's a short between the 5V and ground wires coming from the N64, remove the wires and then check for a short between the output of the 5V regulator and ground on the N64 motherboard. If the short is still there, examine the board for any stray solder or solder bridges. If the short is resolved after removing the wires then the issue was with the wiring.

Some other questions:

1. Did you do the checks from my previous post?
2. Do you have pictures of your installation on the N64 motherboard?
3. With the board removed do you get audio on the analog output of the N64?
4. If you happen to get your receiver to detect a digital audio signal from the board again do you get audio on the analog output of the N64?

[GK6475]

A short between 5V and ground when everything is hooked up but unpowered is not normal.

When you say that 5V and ground are not shorted when you remove the board from the N64, do you mean between 5V and ground on the board, or between 5V and ground on the N64? If you only checked the board, also check between 5V and ground on the N64. If there's a short between the 5V and ground wires coming from the N64, remove the wires and then check for a short between the output of the 5V regulator and ground on the N64 motherboard. If the short is still there, examine the board for any stray solder or solder bridges. If the short is resolved after removing the wires then the issue was with the wiring.

Some other questions:

1. Did you do the checks from my previous post?
2. Do you have pictures of your installation on the N64 motherboard?
3. With the board removed do you get audio on the analog output of the N64?
4. If you happen to get your receiver to detect a digital audio signal from the board again do you get audio on the analog output of the N64?

I'll have to try modifying the 5V and GND wires to see if I can make them not shorted. It only happens when the 5V wire is hooked up to the board, but all of the other wires are still connected, including ground. I did check RST, the coax hookup, and the oscillator, so they check out (before the 5V shorting problem developed, at least). I did not check IC2's pin 6, I'll have to check that out and see if it is causing any issues. I'll have to get some pictures of it when I am next available to tinker with it, as it will require unscrewing the heatsink assembly (I guess I really should just leave it unscrewed while doing this sort of thing). Analog audio has been unaffected so far, it seems, though the last time I checked it was a few modifications ago, I think it still worked even when the receiver showed a blank signal. I may try to completely rebuild a board with a fresh PCB. I ordered 3, so I'll have to find the last board.

[GK6475]

Is there not a way that I can just order a pre-made board? Or, if I could get some boards from a cheaper manufacturer, like PCBWay, then I'd have more attempts to get it right. When soldering SMD components, PCBWay's boards work better for me for some reason. All of the SMD circuits that I've put together on their boards have worked well.

[L-Train]

Is there not a way that I can just order a pre-made board? Or, if I could get some boards from a cheaper manufacturer, like PCBWay, then I'd have more attempts to get it right. When soldering SMD components, PCBWay's boards work better for me for some reason. All of the SMD circuits that I've put together on their boards have worked well.

Unfortunately I can't offer pre-made boards, and as far as I'm aware there aren't any modders who are publicly offering board assembly services.

I've created Gerber files for the board and they're available here: https://drive.google.com/file/d/1npOJY1 ... drive_link. They were created using the original Eagle .brd file as well as the CAM preset from JLCPCB (which is the PCB manufacturer I recommend). However, since I haven't gotten these Gerbers manufactured myself I can't provide any guarantee on the accuracy or correctness of the boards they produce.

If you go with JLCPCB there are a few changes to their default 4-layer configuration that I recommend:

• Material Type = FR-4 TG155. This material has higher heat resistance and allows for rework with less risk of delaminating pads.
• Specify Layer Sequence = Yes. Although it's not required to specify the layer sequence I tend to do this to ensure the correct order. Specify this layer sequence and double check that it's correct:
  • L1 (Top layer) = da_src_copper_l1.GTL
  • L2 (Inner layer1) = da_src_copper_l2.G1
  • L3 (Inner layer2) = da_src_copper_l3.G2
  • L4 (Bottom layer) = da_src_copper_l4.GBL
• Mark on PCB = Remove Mark

The defaults for everything else should be okay. With the board configured as above, the price for 5 boards is $5.21 USD and 10 boards is $10.23 USD. Their "Global Standard Direct Line" shipping service is quite inexpensive as well at only a few dollars. It's been quite reliable for me, usually taking only 2 weeks from ordering to delivery in Canada.

[GK6475]

Is there not a way that I can just order a pre-made board? Or, if I could get some boards from a cheaper manufacturer, like PCBWay, then I'd have more attempts to get it right. When soldering SMD components, PCBWay's boards work better for me for some reason. All of the SMD circuits that I've put together on their boards have worked well.

Unfortunately I can't offer pre-made boards, and as far as I'm aware there aren't any modders who are publicly offering board assembly services.

I've created Gerber files for the board and they're available here: https://drive.google.com/file/d/1npOJY1 ... drive_link. They were created using the original Eagle .brd file as well as the CAM preset from JLCPCB (which is the PCB manufacturer I recommend). However, since I haven't gotten these Gerbers manufactured myself I can't provide any guarantee on the accuracy or correctness of the boards they produce.

If you go with JLCPCB there are a few changes to their default 4-layer configuration that I recommend:

• Material Type = FR-4 TG155. This material has higher heat resistance and allows for rework with less risk of delaminating pads.
• Specify Layer Sequence = Yes. Although it's not required to specify the layer sequence I tend to do this to ensure the correct order. Specify this layer sequence and double check that it's correct:
  • L1 (Top layer) = da_src_copper_l1.GTL
  • L2 (Inner layer1) = da_src_copper_l2.G1
  • L3 (Inner layer2) = da_src_copper_l3.G2
  • L4 (Bottom layer) = da_src_copper_l4.GBL
• Mark on PCB = Remove Mark

The defaults for everything else should be okay. With the board configured as above, the price for 5 boards is $5.21 USD and 10 boards is $10.23 USD. Their "Global Standard Direct Line" shipping service is quite inexpensive as well at only a few dollars. It's been quite reliable for me, usually taking only 2 weeks from ordering to delivery in Canada.

This helps loads. Thanks a ton, I'm sure I'll be able to get it working with these. The ones on OSH Park are decent, but do not fare well for resoldering.

[GK6475]

It's been a bit, and I recently decided to revisit this project. I was able to get one of my boards to output the same blank signal again, though I have continuity tested everything and I have checked every chip for shorts. I also rechecked the four things that you mentioned previously, and all came out fine. I checked my input wires, and all of them are connected where they need to go on the N64's board. I tried with and without 47 ohm resistors inline for each audio pin. I'm about to just rebuild the entire thing on one of the new boards that I have, but I wanted to see if I can get what I currently have to work. Is there anything that I can do from here? I hope that my chips aren't faulty or something.

https://imgur.com/a/JKOpkiC

[jd213]

The soldering still looks pretty iffy (no offense meant). Might be a good idea to apply some flux and re-flow each joint.

[GK6475]

The soldering still looks pretty iffy (no offense meant). Might be a good idea to apply some flux and re-flow each joint.

I know, I already tried reflowing. I tested for continuity and shorts everywhere after reflowing everything. At this point I'm thinking it may be best if I invest in a heat gun and start over, because I am at a loss with my current board. I just wanted to know if I could somehow get it to work.

[L-Train]

It's been a bit, and I recently decided to revisit this project. I was able to get one of my boards to output the same blank signal again, though I have continuity tested everything and I have checked every chip for shorts. I also rechecked the four things that you mentioned previously, and all came out fine. I checked my input wires, and all of them are connected where they need to go on the N64's board. I tried with and without 47 ohm resistors inline for each audio pin. I'm about to just rebuild the entire thing on one of the new boards that I have, but I wanted to see if I can get what I currently have to work. Is there anything that I can do from here? I hope that my chips aren't faulty or something.

https://imgur.com/a/JKOpkiC

Hey glad to hear you haven't given up on it. There's one wiring issue I see, the wires for coaxial output are wired to the optical output pads. The red wire for the center RCA pin should connect to D+ and the brown wire for the shield should connect to D-. Once you've done that, and if you haven't tried already, try to see if another device can lock onto the coaxial S/PDIF signal.



There's also this connection to the via coming from pin 6 on the RCP. It might just be brown flux residue underneath that makes it look like it might not be connected fully, but can you reflow this and test continuity from the top of the RCP pin (not the via connection) to the SRC board?



The input pins on the left side of IC2 look like they could also use a reflow:



Strongly consider cleaning all of your solder joints on both the N64 and SRC board with 99% IPA like I described earlier. It might reveal some things under the flux residue.

[GK6475]

Ok, I reflowed those pins, and much of the rest of the board again, and I cleaned it with some alcohol. I also rewired my wires to the DENC chip instead using smaller wires, and they do connect all the way through to RCP pins 6, 7, and 10. I forgot to mention, I did try it on both OPT and GND as well as using D+ and D-, just to see if there was any difference, and there was not. So far, the results are the same, still a blank output that my reciever thinks is active. I wonder, is it worth trying to wire the N64's audio pins directly to the CS8406? My amp is tolerant of my SNES over direct SPDIF, so I know it would accept the N64's sample rate. I know that the N64 doesn't have a master clock of its own, but maybe the 24MHz oscillator will work with its signal?

The pins are not shorted in person, and everything looks well-connected to my eyes. My camera does not do it justice. https://imgur.com/a/n64-digital-board-JKOpkiC (added 2 images of the updated installation).

[L-Train]

Thanks for the clearer pictures. Your soldering looks okay. The pad for pin 3 on the SRC4192 is missing but it's not connected to anything so that's okay. Where did you get the CS8406 and SRC4192 chips from? The CS8406 doesn't look like ones I've bought from DigiKey in the past. Yours has the "C" symbol from Crystal Semiconductor which means it might be very old stock. The SRC4192 looks closer to mine, but the Burr Brown "BB" logo looks small and not wide like the BB logo typically is. Here's a comparison between yours and mine:

Spoiler

The packages appear identical and the markings are laser etched so I'm inclined to think yours are genuine, but if they were salvaged then whether or not they work correctly is up in the air.

To aid with your troubleshooting here are images of the SRC board's top and bottom layers:

Spoiler

Zoom into the images to see what pins/pads are connected to what signals/nets. Probe around your board to confirm that everything's connected to where they should be and not where they shouldn't.

Does your receiver show what sample rate the digital signal is? If so, does changing the output of the board from 48 to 96 or 192 kHz show the correct sample rate?

As for connecting the N64's digital audio pins directly to the CS8406 I don't think it'll work without the correct master clock. And even then, I don't know if receivers can accept some of the weird sample rates it can output.

[GK6475]

My reciever doesn't show the sample rate, as far as I'm aware, but I know it works with my SNES's generally off-spec digital audio signal, with all games. Where can I source a genuine CS8406? They don't seem to be in stock on DigiKey. I may try to get some SRC4192IDB chips from them, though, since my current ones are from a less reputable website, and were cheaper. Maybe I have been dealing with defective or non-genuine chips all along.

Update: I did order a new SRC4192IDB from DigiKey (the exact part from the BOM), now I just need a reliable source for the CS8406-CZZ.

[L-Train]

This issue seems like a problem with the input so you might want to also try replacing the SN74LVC86A in case something's wrong with it.

Since Cirrus Logic discontinued the CS8406 a few years ago we won't be able to find them at trusted distributors, but I did find this listing on AliExpress: https://www.aliexpress.com/item/1005006194721225.html. If the picture of the part is representative of their stock then it looks legit as it's almost identical to one I have with a 1746 date code. I just bought a few to find out

[GK6475]

Thanks, I've ordered a couple of those chips, and I plan on rebuilding the board with fresh components anyways, once I get everything. I've figured out how to solder the chips in a better way, so hopefully it was just bad chips all along.

[GK6475]

Good news, it WAS the chips that caused the mod to not work! After rebuilding the board with an official SRC4192IDB and the CS8406 from Aliexpress, I was able to finally get it working! Thanks for your help throughout this, my N64 sounds amazing now.

[Gunstar]

Good news, it WAS the chips that caused the mod to not work! After rebuilding the board with an official SRC4192IDB and the CS8406 from Aliexpress, I was able to finally get it working! Thanks for your help throughout this, my N64 sounds amazing now.

Awesome to see you stick with it and get there in the end.