I built, & still have in working condition, the Syntom from the "electronics & Music Maker" (E&MM) magazines, from the early to mid 80's
It is a great little circuit, i this I may have seen a reprint of it, on a web site somewhere. I still have most of the E&MM mags that i managed to buy from back then. sadly I don't have a scanner.
The Syntom can do most of the sounds that you hear on the Amdek, that yo linked to. You can strike the Syntom like a percussion synth, & I also added the trigger input mod, that was in a later edition of E&MM.