Any good ideas for a monophonic keyboard for synth

Thread Starter

Surgent Gaming

Joined Feb 26, 2018
I am trying to build a monophonic synthesizer. The big problem I'm having now is that I have a keyboard and I want it to output a single note CV and gate. I have tried using resistors, but if you press two keys, you get a signal with the sum of the two keys.

If you have any good schematics please post them.


Joined Jun 5, 2013
What do you want it to do when you press two keys?

I suppose you would use some kind of double pole switch that would disconnect, say, all the lower keys from the circuit when any key is pressed. This would mean that the higher key would always be the one that is sounding when two keys are pressed.


Thread Starter

Surgent Gaming

Joined Feb 26, 2018
Lets say I press the A key. The keyboard emits a CV for A. If I then press the G key without letting the A key go, it will jump to the G key. The CV also jumps to G.

Cheers :)


Joined Apr 9, 2011
The old analog synths used to work like your keyboard, they gave the sum of the keys pressed. Some newer keyboards work like you want yours to but they use a microcontroller to do the process.


Joined May 4, 2013
You could try a 1N4148 signal diode is series with each key. A Schottky diode would probably work better but you can start with the 1N4148 to see what happens.

Post the schematic of your circuit for a more complete answer.


Joined Apr 30, 2011
The traditional method uses a scanned matrix. Here's a link to one tutorial. You may find others.

Monophonic "lead" synthesizers still use this method even though they're not polyphonic. They typically have logic that prioritizes either the last key pressed or the lowest note pressed, depending on the trigger or gate setting, when more than one key is held down simultaneously. See page 29 in this manual for one example.