ModyPoly Polysix MIDI pitch bend resistor values effect

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  • #9463
    Anonymous

    Hi,
    I’m installing the ModyPoly kit in a Polysix for a friend.
    I’m curious about the resistors required for the pitch bend support and the instructions are a bit vague regarding the 34k+68k resistor values:
    “Other values are also possible, as long as one has double the value of the other. This will change the maximum pitch bend range.”
    This?
    Exactly what will change the pitch bend range? The ratio between the two resistors? The sum of their values? Both?

    I’m looking at
    https://tubbutec.de/blog/utilising-the- … ix-cv-out/
    and it seems the CV from the ModyPoly is used in a kind of voltage divider circuit with the 34k and 68k resistors and injected to the VCO mod voltage before the CV summing op amp.
    So I assume that the 68k resistor will affect overall tuning since it adds more or less negative voltage to the mod CV, and the ratio between the 34k and 68k will affect the pitch bend range since the voltage ratio will be different. Correct?

    In other words, it should be possible to use, for instance a 33k and a 68k resistor and get slightly higher pitch bend range?

    #9464
    tubbutec
    Keymaster

    Hi,

    the resistors are chosen to have a ratio of 1:2 .
    33k and 68 will work, but the centre pitch will be a bit off. This is fortunately not a huge problem as the centre pitch can be calibrated (Pitch bend calibration, see installation manual)

    #9465
    Anonymous
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