Designing Famicom AV/PSU board with stereo sound. Please advise features

[Volo]

Dear community,

After asking about on this forum, as well as on Reddit for my dream Famicom mod board, I was advised none . Well, you know what they say: if you want something done - do it yourself!

Planned features:

• Compatibility with both HVC-CPU-07 and GPM-02 consoles.
• Acceptance of any PSU (DC 7-16V, any polarity... *might* accept AC of same voltage).
• No modification of console shell (might be necessary to widen one hole for 3.5 mm socket).
• PWM voltage regulator (use of "classic" warm LM7805 is optional).
• Composite Video (AV Famicom schematic).
• Headphones-friendly stereo sound.
• Hardware stereo/mono switch.
• Ability to reconfigure the PCB into a PowerVamp clone (useful, if you don't want to cut traces on Famicom motherboard).

Stereo Specs:

• Square wave channels (i.e. solo instrument) mixed Left: 100%, Right 75%.
• Triangle (bass), Noise (cymbal) and Samples (drums) mixed Left: 50%, Right: 100%.
• Custom chip channel is mixed to the middle.

The afore should produce quite comfortable, reasonably "wide" stereo scape. Credit for schematics goes to Megawalkman - talented high-end Famiclone designer. Stereo may always be switched to mono.

Stretch goals:

• 80s look-and-feel of PCB. Green solder mask, no silly modern logos.
• No SMDs - only through-hole components, nice for recreational soldering. Might sell as a kit.
• Easy configurability by means of solder-jumpers.
• Compatibility with GPM-02 power switch (though it makes the power traces convoluted, might need to drop this feature).

Below you may find a mockup of the modified Famicom as well as draft schematics of the PCB. Schematics might contain mistakes, please don't copy it (I'm numpty).

Once I get home to my Famicom to take measurements, I'll start designing the PCB... War's a bitch.

Please post your thought of the project, point mistakes and advice corrections or features (Power LED? Different port layout?). Feedback is really motivating.

P.S. I might have some spare devices to sell to the community, It would be nice if it were something that community wants.

[Famicom.In.My.Blood]

Hi !

Sorry for those following noob's thoughts, but :

1 - There is already a Stereo Mod, not very satisfying IMO, so this one will be better, right ? What will be differences exactly ?

2 - This mod will be compatible with NESRGB ?

Thank you for your answers and your investment.

[Volo]

Thanks for your questions! Your inquiries are quite reasonable.

1 - There is already a Stereo Mod, not very satisfying IMO, so this one will be better, right? What will be differences exactly?

Most stereo hackjobs I found online aren't really thought-out. I found to be most promising the schematics is from the Russian Famiclone DIY scene (yes, that's a thing!). There is one sound demo online: https://www.youtube.com/watch?v=0IENeqXopUg&t=1823s I like it very much, but would like to swap right and left.
Do you have any other ideas? If I am dissatisfied with this board, I might play with phase shifters, though I doubt that the board shall have any space for those.

2 - This mod will be compatible with NESRGB ?

My mod-board won't be compatible with NESRGB, as the latter has its own PSU/AV board with pretty much the same features.
The ideology behind my project is quite opposite to NESRGB. NESRGB looks and feels like it came from XXI century. I'd like to keep my Famicom in the 80s, only more usable.
My board shall be akin to Backofficeshow's Power Vamp, only beater-featured, having 80s vibe and hopefully cheaper (hence the kit form).

[gorgyrip]

If pwm won't induce noise in the video, then use it.
Back in the day, I tried the simple stereo mod on a NES. I hated it.
A nice idea (i think) is to keep all the parts for the stereo mod in a single area of the pcb, with a rectangle on the silkscreen layer. If the buyer doesn't want stereo, then he won't have to solder all the parts.

[Volo]

19.06.22 SITUATION REPORT

I got myself back to Kyiv! The city is rebelliously civil, safe and peaceful. Though air-raid sirens are annoying at night.
Shops are open, international postage works - I hope sourcing parts won't become a problem.

I've taken the measurements of the PCB... 90x50mm. Now that's a tight squeeze!
Also, my published schematic has at least 3 mistakes. Oh, well, I'll correct those as I go.

Thank you for your questions!

If pwm won't induce noise in the video, then use it.

PWM shall work at approx. 75-100khz and is equipped with oversize LC filter. I expect sine ripple voltage of <0.01V. Noise might originate from PPU itself, though.

Back in the day, I tried the simple stereo mod on a NES. I hated it.
A nice idea (i think) is to keep all the parts for the stereo mod in a single area of the pcb, with a rectangle on the silkscreen layer. If the buyer doesn't want stereo, then he won't have to solder all the parts.

I'd advise against that. Firstly - the PCB is the worst case of "Component Tetris" I've ever experienced. I hardly have space even to place labels, not arbitrary rectangles.
Secondly - the amp is known to be SUPER CLEAN. It would be a pity not to use it.
Thirdly - there shall be a mono switch.

[bsa]

Hi Volo,

No advice from me (I'm a newbie), but just replying to say that I'm following your work with interest, and I'm glad to hear you made it safely back to Kyiv. Take care and all the best with your board.

[Volo]

I recently was given back my Famicom and decided to finish with the project less ambitiously.

I miserably failed to jigsaw through-hole components on the board and resorted to populating most of the PCB with large-ish 1206 passives. I managed to fit everything... barely. However, a revision of the board needs to be made (for reasons obvious in the picture below).



I'm happy with how it fits within the case and feels from the outside. I'd say it legit.

At the moment, the board has its jumpers configured to work with "vanilla" signals - the audio is mono and the video is in all its jail-bar glory. The power is fine - no distortions on screen, the pulse controller chip is noticeably warm, but should be within spec.

Currently, am fine-tuning the values of the components - the voltage slightly low (4,85 V), the bass is gone etc.

I'll start cutting traces and upload screenshots and audio samples of the "unoriginal" signals, once I receive the Composite Add-on for the OSSC. A direct connection to a modern TV distorts the image.