Speech boards for System 7/9, then all Williams audio boards up until early WPC used the 55516 series of CVSD decoder chips for speech decoding. These haven't been available in a LONG time. The WPC-DCS sound boards used a different set of components, and the later WPC's are the ones that have boards available.

I do have a couple ideas I'm working on for System 7/9 speech boards that may translate well to later designs too.... but I've really only gotten into the early phases of this project and keep getting sidetracked.

As mentioned above, it's not impossible just cost prohibitive with limited demand compared to the other boards that have much higher failure rates.

-Hans

Yep, the ASIC's are going to be a future issue for sure. But the WPC era stuff has much better documentation available and the original schematic sheets and such may still be around, so theoretically they may be able to make more of them. The demand will be there for sure and PPS has an interest in keeping CPU boards available.

I believe it's the Yamaha decoders, and for earlier boards it's the 55516 CVSD decoders.

-Hans