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Synthesiser keyboard - cant work out how to hold notes after trigger

Discussion in 'General Electronics Discussion' started by george2525, Nov 26, 2016.

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  1. george2525


    Jan 30, 2015
    Ok so ive been making a synthesiser keyboard. Ive got it working, the notes are more or less in tune and it sounds nice.

    My problem is that it plays a note when no key is being pressed. This is the default oscillator frequency that is present when no control voltage is applied.

    I need it to hold whatever note was last pressed so that when all keys are released it doesn't revert back to the default tone.

    I have been looking at sample and hold. RS flip flops, latches and that type of thing but im lost as to which method to research. I have not managed to find any examples that reference this problem which is making it extra difficult.

    If I use some kind of sample and hold, it needs to be very accurate because the control voltages are very precise and so if i use op amps etc they need to buffer the control voltage precisely.

    obviously when the keys are released I dont want the default tone to be held!

    so I think I need something that holds the last note whenever the control voltage is approximately 0V , say less than 0.05V or so. IE whenever there is no control voltage, the last voltage is held.

    I hope this makes sense.

    Im not asking for full schematics or anything, just to be pointed in the right direction.

  2. tedstruk


    Jan 7, 2012
    you have to make the entire board into a trigger system. after all its called a KEYBOARD.
    now don't take me as a tech.... I'm a really bad [email protected]
    so I would build a simulator keep the notes on, then I would attach a second circuit that fires a switch that acts like a note signal, but with a do nothing app like turns on an LED that says "no note to play" under it
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