/diy/ - Do It Yourself

How were keyboards for old analog synths made?
I can't really find a whole lot of information, most designs either use button matrix and a microcontroller, or are just plain voltage dividers for using with a 555 timer.

This was my best attempt.
The diodes are there so that if multiple keys are pressed, only the highest key will play.
The 20MΩ resistor is to simulate the input current on a real op-amp.
It kinda works, but there's still a 50mv drop across the diodes, which is like half a note when using 1V/Octave, so not that great.
Obviously I could remove the diodes, turning it back into a regular old voltage divider, but then you get weird notes if multiple keys are pressed.
Another solution would be to replace all the diodes with ideal diodes, but that adds quite a bit of cost to the BOM.