
Excerpt:
"The "Roland Rhythm" TR-77 was Roland's very first product, from 1972. It makes its distinctive drum voices from what are called "tuned resonant" circuits, which consist of a capacitor, an inductor and a resistor - very basic!. The patterns are preset rock, jazz and latin styles of 1 or 2 bars. There are no user-programmable patterns, because there is no "memory" - the patterns are hard-wired. That is, they are literally made from a matrix of wires between the transistor flip-flop counters, connected by diodes, to the inputs of the voice circuits, depending on which buttons on the front panel are pushed in (Pushing one in causes the others to disengage, but if you're careful you can manage to get more than one to stay in, giving you a mix of patterns.)
My main motivation for investigating the gubbins of this old beast was to see if there was a way to synchronize it to a source of external clock. I also wanted to know if there were any good voice mods possible. But another reason was that I wanted to understand how this basic type of pattern sequencing worked, because my amateur electronic explorations hadn't really covered this so far." You can find the videos and full details on A Disco Ate My Baby.
The following is the TR-77 after being modded:
77demo.m4v
YouTube via TheRealADAMBABY