No WAV playback with Sega Nomad

[munchluxe63]

I just got my Mega Everdrive and tested out the WAV playback function; it doesn't work with my Sega Nomad, but it works with my NTSC Model 1 Genesis and certain demo ROMs that appear to have a similar PCM playback feature work.

When the file is opened on the Genesis, it plays as expected, but on the Nomad, only a faint interference noise, no audio.

GYM playback and Genesis games work as expected.

Some more information:

System Type: US NTSC
Firmware Version: 6
OS Version: 8
Assembly Date: 22-05-2013 20:15:8

[KRIKzz]

WAV player use stereo dac inside of cart, but expansion audio lines was removed from nomad

[munchluxe63]

Oh, I see. Which lines from the cart slot to which pins on the on-board chips need connecting? (I've already connected successfully the SMS mode enable line.)

[Chilly Willy]

It needs more than connecting the cart edge pins - it needs the audio circuitry to mix with the built in audio as well. It's a big mod, but I think Tiido did that... you might check the Nomad mod threads over at Sega16.

[munchluxe63]

I'm down for it; I have some spare perfboard and probably at least half the components on hand already.

Thank you.

Edit:
I've searched around for a while, but I haven't found a thread.

[Chilly Willy]

It would probably be easier to just PM TmEE.

[munchluxe63]

Yeah, I gave up and sent him a PM.

[Chilly Willy]

Once you get something worked out, you might consider making a thread on it. I'm sure there are probably others who could benefit from your experience. 

[munchluxe63]

Sure; just have to get my Model 2 back so I can take a look at the circuitry and see how it's mixed.

It would help if I knew which pins the Mega Everdrive's DAC outputs to on the cartridge, though. (I don't even know where the DAC is, although I'm guessing either B1, B2, or B3...)

[villahed94]

Actually it would need some pin lifting. Sega wired both input pins (32X and SCD) on the 315-5684 to GND, but other than that it's possible.
I would however implement a different circuit as that amplifier chip is really noisy

[munchluxe63]

Actually it would need some pin lifting. Sega wired both input pins (32X and SCD) on the 315-5684 to GND, but other than that it's possible.
I would however implement a different circuit as that amplifier chip is really noisy

Yeah, I was thinking of just replacing the whole amplifier circuitry anyway; so much needless noise, and it would make this a bit simpler... I spent the past 7 hours or so tracing PCB photographs in GIMP editor and reading block diagrams (for some reason, they're in Greek [and also PAL]) to figure out how the MegaDrive's audio circuitry works. I don't really know how the Mega Everdrive manages stereo WAV audio, but I'm trying to figure it out; I'm guessing it uses two of the CARTEDGE pins, B1 and B3? Once I get my hands on my NTSC Model 2, it would make things a lot easier; maybe someone could explain the process to me?

I dug up this and I guess I'll try to work off of it; sketching things out in Fritzing. I'll have to go out and buy some parts.
http://arcade.ym2149.com/megadrive/mdsndmodv3.jpg

[Chilly Willy]

If you're going to use the CCAM, use the latest. Tiido (TmEE) has a sticky thread at Sega16 for the CCAM:

http://www.sega-16.com/forum/showthread.php?7686-Crystal-Clear-Audio-Mod-for-Sega-Mega-Drive-2-amp-Genesis-2-version-1-0

Actually it would need some pin lifting. Sega wired both input pins (32X and SCD) on the 315-5684 to GND, but other than that it's possible.
I would however implement a different circuit as that amplifier chip is really noisy

I did not know that. That's interesting info.

So if you didn't care too much, you COULD just solder a couple lines (and lift the pins). Using something based on the CCAM would sound much better.

[munchluxe63]

On second thought: since it's a PORTABLE system that I run on a homemade battery pack of 8 NiMH batteries and CCAM will use a bunch of extra power (the Mega Everdrie already lowers my battery life SUBSTANTIALLY; I now need an extra set of batteries), it might not be a great idea. I'm not too bothered with the terrible sound quality, although it would be nice to get the M.ED's PCM working. I'm quite busy, but I'll see if I can do something "cheaper" within the next couple of weeks. (I'm that busy.)

[princemoonrise]

I've just managed to enable Mega Everdrive WAV playback on my Nomad! (along with full 32x audio functionality, SMS FM sound, among other things...)  It is indeed cart port B1 and B3 being not connected, they need to be connected to pins 24 and 10 respectively on Sega IC 315-5684, by way of .022uf capacitor and 47k resistor for each connection, and the surface mount pins do need to be lifted off of the PCB so the solder operation is not for the faint of heart.

ITS GREAT!  Bad audio quality or not, the Nomad makes a great little portable audio player.  Since my Nomad has a replaced screen and runs off of lithium ion rechargable camera batteries, power isn't a problem as it lasts hours on a charge.

Thanks for adding the wav playback feature onto the Mega Everdrive, Krikzz.  I like how it goes down the list of files in sequence so you can make "playlists" by arranging them in different folders.  Hopefully we can get more options in the future for wav playback.  Main inconvenience is having to convert everything to 8 bit 22k, but its well worth it!

[Chilly Willy]

Thanks for posting your findings.

And the exact frequency you should use is 45 MHz / 2048 == 21972.65625 Hz.