IIGS audio

LiteSound

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.

You can find partially made cables on eBay by searching for 7 pin 2510 or KF2510 cables, 30cm long.
This length is "about right" and will reach all slots. Pin 1 on the J25 goes to pin 7 on the LiteSound board.
This is basically flipped or wired backwards. Yeah, I should've caught this and may someday fix it.
It's easy enough to just wire this way! Included is a closeup photo of both ends of the cable, one end attached to the PCB, and the other with the alignment tabs for the J25 end clearly visible.

The pins I use are Molex 16-02-0103 on the LightSound end, and the housings are Molex 50-57-9207.

I'm using a 74HC4052D demultiplexer and a TL074CDR quad audio op-amp. There are other pin-compatible chips that can be substituted.

The headphone jack I use is a CUI Devices SJ1-3515N and the 7 pin header is an Amphenol 77315-124-07LF.

Current(ish) board rendering: PCB rendering

This rendering shows a 2 pin header that was added at the request of about two people who wanted the ability to power this board externally.
This is not the norm, but you can do it if you really want to. It's your GS, you do with it as you please! This doesn't mean external to the case, just external to the slot (with +/-5v wires run to the pcb) so you don't have to tie up a slot. This is on you to figure out how to do. The only ground on this board is the analog ground on the J25 header on the motherboard. Don't tie analog ground to digital ground (it says so right on the GS schematic). This will introduce noise, as will decoupling capacitors between +/-5v and digital ground. That's why they're not on the board.

This is technically the 4th revision of the PCB. 1st rev worked fine, but was too short for PCBWay to be able to bevel the card edge. 2nd rev was bigger with some parts moved around where it would be natural to accidentally pull the audio coupling capacitors off the board. Initially I was using low profile SMT tantalum capacitors for this. People had a real problem with the idea of using tants so I switched to the SMT electrolytic caps. 3rd rev moved those caps to where they are now, but also included coupling caps for the power supplies to DC ground. I learned the hard way not to do this. Don't do it. Noise will be introduced. 4th rev removed those two capacitors and added the two pin header.

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.