Putting a YM2203 FM soundchip in place of the YM2149

[unseenmenace]

I posted about this idea over on Atari-Forum and Joel Olsen suggested here might be a better audience for it :)

I'm working on a music composing program for the ST and thought it would be a good opportunity to implement support for a better soundchip in an ST after remembering an old thread about the possibility some while ago:
https://www.atari-forum.com/viewtopic.php?f=15&t=6520

After looking at a load of datasheets I settled on using a YM2203 as it seems to be the closest to the YM2149 in terms of connections and operation, and I think I'm pretty much finished with the design of the PCB now. If anyone on here is experienced with this kind of thing I'd be very happy to hear any suggestions or criticisms.

The bus control pins were the biggest challenge as upon consulting The Bible (ST Internals) it appeared that the ST keeps one of the control pins on permanently and only adjusts 2 of them, so I had to use the 2 logic chips and some diodes to adapt that to the signals the YM2203 needed.

Bus Translation.jpg

This is what I've come up with:

PCB.gif

It has separate outputs for the SSG and FM outputs and connections for a double-pole switch to combine them as desired.

I should note that credit for the amplifier circuitry (and how to hook the DAC up) goes to Zenmai from his YM2203 Jukebox project:
https://github.com/zenmai/YM2203_JukeBox

[exxos]

Is there any real difference from the 2149 then ?

Also, there's no need to impedance match tracks.. If anything it will probably make signals worse.

[unseenmenace]

Is there any real difference from the 2149 then ?

Yes, it has 3 FM voices in addition to everything the YM2149 has and they are accessed in the usual way but with some extra YM register numbers.

Also, there's no need to impedance match tracks.. If anything it will probably make signals worse.

I have since been told that it's unnecessary (on Facebook), so I'll give the traces more space instead, thanks :)

[PhilC]

Interesting project, I'll look forward to hearing the results

[unseenmenace]

I'd appreciate it if anyone could check that my logic in the above spreadsheet table is sound. Between the 2 YM datasheets and ST Internals, I'm fairly happy everything else is good :) This is the current PCB, and I'd be happy to send the file if anyone wants to see what's going on more closely:

PCB.gif

I've ordered some YM2203s, Y3014 DACs, DIP-40 sockets and pin strips from AliExpress and I'll get the other parts from closer to home once I'm confident enough to get a handful of PCBs ordered.

[joelolzen]

Glad to see you made it here ;)

I never knew about this chip until I heard about your project, and I mean, a better upgrade to stfm sound than this if it can be done, I think is hard to beat.

The sound this chip can produce I believe is the perfect evolution of sound on the ST.

Hope you get help with your questions and support from all the smart people hanging in here 8-)

Here’s an example of the 2203 plying all its six voices
https://youtu.be/qSWCihT_2Ho

Joel

[exxos]

That does sound pretty cool. Has more of a synth vibe to it than chip.

[SophieRose]

An interesting project, looking forward to seeing this progress. 8-)

[unseenmenace]

Glad to see you made it here ;)

I never knew about this chip until I heard about your project, and I mean, a better upgrade to stfm sound than this if it can be done, I think is hard to beat.

The sound this chip can produce I believe is the perfect evolution of sound on the ST.

Hope you get help with your questions and support from all the smart people hanging in here 8-)

Thanks Joel :) The YM2203 was used in LOADS of early arcade games as well as the NEC PC-98, popular in Japan in the 90s, which is why there are so many good tunes out there written for it.

That does sound pretty cool. Has more of a synth vibe to it than chip.

It is actually a full blown 3 channel synthesizer bolted onto a YM2149, and the predecessor to the soundchip in the Sega Megadrive. Each channel has 4 oscillators and the 3rd channel can be switched into a twin 2 oscillator mode or a quad single oscillator mode, i.e. 2 notes at a time with a less complex waveform, or 4 notes at a time playing a pure sine wave.

An interesting project, looking forward to seeing this progress. 8-)

Thanks, hope it pans out as I've ordered some of the parts and plan to get the PCB's made as soon as I'm confident enough there's half a chance of them working :D

The plan is to fit one to one of my spare STFMs and check the standard YM2149 features work first, then code a quick and dirty VGM file player as, much like YM files, they are just register dumps that can be streamed into the soundchip :)

Render.jpg

[unseenmenace]

So these have arrived so I'm hoping somebody here might be able to give my conversion table and design a look over and see if I've done anything dumb.

YM2203C.jpg

If it looks good to anyone with a bit of knowhow then I'll be a bit more confident about getting some PCBs ordered and see if I can make this work :)