This is a stub article - because I failed at making it simply short and done.

In 1987 -- nearly 40 years ago as of writing in 2026 -- Casio added the CT-510 to their stable of (music) keyboards.  Not much later ('88?) one came into the hands of this non-musician and has lived its decades mostly out-of-sight-out-of-mind except for occasional reinterment after a move. Now I want to re-arrange half the room where it's stashed and this time seemed like a good time to let it go.

It wasn't supposed to be a project.

But I forgot that the "close enough" AC wall wart that I'd chucked in the box ages ago passes too much 60 Hz ripple to be good for anything but function testing -- which is what I was doing that wasn't supposed to be a project. And then I blew right past the atrophied neuron that would have started looking for hum at the power inlet. So I found some other stuff along the way to where I didn't start. 

Then I thought the animated GIF above and a small number of words would suffice to close out this not-supposed-to-be-a-project so I could get back to re-arranging half a room so I could [...] in order to [...] and [...] to [...] because [...] so [...]. But then, on the very cusp of snatching closure from the jaws of distraction, I found the second component of the "melody" signal. (The "instrument" I was playing with uses it only for note attack so it was mostly silent most of the time I was wondering what that pin was for.)

But I'd already packed up the setup for shooting scope video. So much for closure. I took some photos of the interesting board and boxed it all up again because not supposed to be a project.

...Rabbit hole...

I think I've got a pretty good idea of what happens on the mix+amp board now, which includes some things that might be interesting and not already old news among the circuit bending crowd, but haven't re-un-boxed the thing to check out what I think I've figured out.

to be continued ... maybe