Now, I'm familiar with the Yamaha DX7. I was born in the 70s and grew up in the 80s, so was awash in the tell-tale tone of the legendary synth wherever there was what passed for music at the time. (I was also familiar with it being used as a prop for bands miming away on Top of the Pops - so much non-FM synthesis from a synth not even plugged in!) And now, here we are, a quantity of decades later and Floyd was letting me know that I could effectively have not one but eight of my own. I had to try.
I had just enough hardware knocking about to build what I'd consider the minimum circuitry required on a breadboard, and after work I put together parts salvaged from earlier abandoned projects. Plugged it in and, in a world first, it worked straight away - and it sounded really good, even through the crappy Pi analogue output. Time to make a proper Pi HAT to keep it all together nice and neat, and to have a much better audio output from a PCM5102A board splodged on top.
A bunch of soldering later and I was at the stage shown at the top of the page (more or less... foreshadowing...). Attached the little keyboard I use (a Korg nanoKEY2) and it was all great! Then I tried turning the rotary encoder and this time nothing seemed to happen. Odd, but not terribly so because the encoder I'd harvested from earlier times was a bit scuzzy. So I clicked it to get into the menus, pushed 3.3V straight to ground and destroyed my Raspberry Pi 3B+ (which is, at time of writing, made of pure unobtainium).
Dear reader. Dear, dear reader. Look at schematics when you're assembling things. Don't glance at the wiring you've got on a breadboard and think to yourself, "yeah I've got this lol!!!1!1!" and get the order of the pins wrong.
After swearing to myself a bit (a lot) and a post mortem - and failed attempts to raise the dead - I rewired the encoder and dug out an old Raspberry Pi B+ from the Before Times (we were still in the EU and Obama was still the POTUS - remember those days?) which I could handle destroying more than the 3B+. This time - this time - it worked perfectly. The lesson to be learnt here is Don't.
Further entertainment came in the form of the heavy USB lead for an Arturia Beatstep pulling the light PCB stack off the desk, ripping off a couple of the wires to the LCD in the process. (Spot the hot glue strain relief now.)
Now, I'd wanted to use the power of the more modern Pi to get the eight DX7 voices and effects-a-plenty but the more pedestrian single core oldster Pi can only do one voice and no effects to write home about. But as it turns out, that's ok! It's actually easier to understand what's going on with the single voice and it brings an old Pi back into use (albeit at the cost of a newer one, grumble grumble).
I'm not even close to being the only one doing this. Look at these fine fellows!
- https://diyelectromusic.wordpress.com/2022/04/28/bare-metal-raspberry-pi-minidexed-dx7/ - Kevin's site is a site of wonders
- https://lookmumnocomputer.discourse.group/t/8-fm-poly-voices-in-one/4930 - some Look Mum No Computer forum members (including myself and Kevin there) doing similar things
- https://youtu.be/Z3t94ceMHJo - remember Herr Steinberg? No? Really?
And of course, https://github.com/probonopd/MiniDexed is where it all begins.