As you may have seen in my previous post, my Kawai R-100 Drum Machine came with a 3-EPROM “soundswitcher”. Since this is no longer available, I thought I would make my own. It’s not an exact clone of the Drumware Inc board. First, I used different logic … just a personal choice. Second, I eliminated the ribbon cable to cut down on cost. It looks like there is just enough vertical room to pop the board on top, so that’s what I did. In my unit the Kawai ribbon cables are such a mess that it’s hard to close up the lid already. Finally I did a 2-layer board compared to the old Drumware single-layer board that was probably taped up by hand. In fact this is how I used to make SRAM memory expansions myself in the late 80′s. I even advertised them in the back pages of Polyphony magazine (for JX3P, OB DX, Polysix and a few others).
Anyway, I have a couple of spare boards. They weren’t particularly cheap as I only had a few made, but if you want to buy a blank, let me know. They will probably be in the area of $50USD. The other parts needed are sockets, round header pins, a 74HC138, two 4k7 or 10k resistors, some 0.1uF caps and one 10 to 100uF polarized cap. You also need the EPROMs and one SPDT 3-position on-off-on toggle switch. See the photos for more detail.
I also silk-screened the pin information on the top for people that are circuit-bending maniacs. This should give you a head-start locating bend points without trashing your existing hardware.
Read my previous post for more background info.