This is a simple two-SID-chip plug-in board for the American Commodore 128-DCR.

Although it isn't intentional, this board may also fit "flat" C128's and plastic-case C128-D, and C64 motherboard assemblies #250407 and #250469 (but not any of the others). For those machines, it would be better to use the stereo board designed specifically for them:

https://www.pcbway.com/project/shareproject/C64_C128_Internal_stereo_SID_17f28143.html

The second SID can be placed in any I/O page the machine supports, and it can be moved off of the base of the I/O page you put it in and placed at any other $xx20/40/60/... section therein, if desired. You can also put it in the $D400 page just above the primary SID.

This board has provision for the "digi-boost" hack also, to make 8580 digital sample playback louder.

For more details on wiring/installing, see the README, attached below (it's also in the git repository).

Note: you may need to trim the pin header that goes under one of the sockets, depending on how long the top halves of the pins are and how tall the socket sits off of the board.

Part substitutions are fine as long as the bottom-facing pin headers are the round machined kind (there's also a fairly rare kind that have thin, flat pins -- those are fine too). I strongly favor Mill-Max machined-pin sockets for the SIDs, but plain old "double-wipe" style will do also. Commodore specified that the 22000 pF capacitors should be poly-film type, but ordinary modern ceramics will probably be just fine.

This project is a by-hand full redraw of a working design I originally made with gEDA, but now re-done with KiCAD. Although this version HAS NOT BEEN TESTED, its base schematic is identical to the redrawn C64/128 version linked above (apart from some minor differences in component values and footprints). That board works, so this one should also.