This card provides stereo audio capability for the Apple IIGS computers.
This project was done in KiCad 6.0.10 and may not work with older versions.
Installation and use manual is a Google Docs file and can be found at this URL: https://tinyurl.com/39kpvvwv
The J25 header on the IIGS motherboard provides an analog audio signal, and address lines to drive a demultiplexer which splits audio into Left & Right audio channels.
I'm using a 74HC4052D demultiplexer and a TL074CDR quad audio op-amp. There are other pin-compatible chips that can be substituted.
Current(ish) board rendering: PCB rendering
Known issue: This stereo sound card makes a chirp / squawk sound when the IIGS is switched off if a Reactive Mircro power supply is installed. This does not happen if your system uses an original power supply and does not impact performance in any way. It may do the same with other aftermarket power supplies. YMMV.