Modding older consoles for Digital S/PDIF audio?

[brendanraymond]

Unfortunatly... it isnt possible using that technique for 2 reasons.

The sixth channel can act as a surrogate PCM channel by means of the 'DAC Enable' register, allowing the chip to play 8-bit PCM sound samples. Enabling the register disables FM output for that channel. PCM data is written to the channel via an 8-bit register. The YM2612 does not provide any timing or buffering of the PCM samples, so all frequency control and buffering must be done in software by the host processor.

The YM2608 6th channel to my knowledge doesnt support 8 bit PCMs unlike the YM2612. I too thought it was a great idea until Tiido Priimgi pointed that one out... Also, the second reason is that the YM3016 DAC is designed to couple with this chip... Yamaha probably having an exclusive format... but I cant say difinitivly that they are exclusive to those 2 chips.

The best way I can see it is to use a chip like the CS5361 or coupling a CS5330A/31, 74HC74, 74HC00, LM 7805 and a 12.288MHz oscillator... That way you can have full control over your mixing circuits between the MegaCD and 32x which would be another nightmare alltogether to mix as SPDIF. The other advantage is that you can customise the opamps, caps and mixing volumes to your personal tastes too... there is ALOT of audiophile gear that is up to the task of perfect audio buffing for our application.

I have a fairly clear idea what needs to be done, I just need the time to assemble it and tune some opamps up and do some tests... but I am rather short on time at the moment.

If its any interest to you... here is probably the most uptodate thread on the design of the mod: http://www.sega-16.com/forum/showthread ... 361&page=2

Keep in mind I have been learning about electronics etc on the fly here... so it will get busy when I start finalising the design of the op amps.

[brendanraymond]

Also, just to clear up any confusion, my SPDIF saturn mod is complete and my SPDIF MD is still a work in progress... and is looking promising!

[Mod_Man_Extreme]

Ummmm, potato?.......

I've never really worked with insane amounts of stuff like that, my experience stops at replacing caps and mostly getting single wires and chips in and out of machines.

[brendanraymond]

maybe we can make it a team effort! I'm going to be studying opamps in depth soon so I will be taking measurements of voltage levels of different channels (MD, SegaCD) maybe you could help me work out how much we are amping on the 32x? Do you have a 32x?

Its a big job to do on ones own, so I guess the more help the better ^^

Oh, and as far as the Jaguar is concerned... I would be looking up the audio chips they are using... perhaps they have seperate DACs if you are lucky

[Mod_Man_Extreme]

Did some more research and found this:

http://nemesis.hacking-cult.org/MegaDri ... slated.PDF

From what I read and the bit I understood it should operate with the same 8-Bit ADPCM input as a Genesis shouldn't it?

Like I said though, I'm not knowledgeable about IC diagrams and circuits at all so this is mostly me trying to understand what I'm reading.

[Mod_Man_Extreme]

Did some more reading on the Jag too and Wikipedia says the system contains two DAC's with one for each channel.

CD-quality sound (16-bit stereo)

* Number of sound channels limited by software
* Two DACs (stereo) convert digital data to analog sound signals
* Full stereo capabilities

Is it possible to generate a single Coax output from that setup? I'm just confused as how to wire up the feed from the two digital channels into one single output.

[brendanraymond]

you might get lucky and just hook up CS8406 or something similar. A toslink connection would be better.

anyway, I gotta get back to work >_<

[Mod_Man_Extreme]

I'd use Toslink, but I only have two inputs and they've been filled by the CD Player and the PS3.

That just leaves me with the Coax Jack which works perfectly for me as I've got a splitter box I could run it and multiple others through. I'm gonna read up a bit more on the standards and such to get it all nailed down.

[brendanraymond]

I'd use Toslink, but I only have two inputs and they've been filled by the CD Player and the PS3.

That just leaves me with the Coax Jack which works perfectly for me as I've got a splitter box I could run it and multiple others through. I'm gonna read up a bit more on the standards and such to get it all nailed down.

using toslink is only a tiny bit easier... you save yourself a total of two extra resistors.

I'll post you a link how to connect up the coax to the chip tomorrow.

anyway, its my birthday today... and its 2:30 am... and my room smells like paving paint cause i've been renovating >_<

[Mod_Man_Extreme]

Thanks man, and Happy B-Day!