The RC2014 retro Z80 8-bit computer was desperately lacking any kind of sound card, so I created one based around the Yamaha YM2149 IC, as used in the Atari ST and ZX Spectrum 128.
It was an interesting project, and I learnt about PCB design and manufacture to boot :)
The board is Open Hardware, with Gerbers and schematics available on GitHub: https://github.com/electrified/rc2014-ym2149
I also sell the PCBs on Tindie https://www.tindie.com/products/edbrindley/ymay-sound-card-pcb-for-the-rc2014-computer/