Late addendum for DOD 440

[Mark Hammer]

Can't believe it waited 33 years, but I stumbled onto a confirmed mod from a DOD engineer for the 440 envelope filter in a 1981 issue of Polyphony.

There is a 430k feedback resistor in the filter stage.  Stick a 100k pot in series with it and you have variable resonance.  For those with a built box and nowhere to install a pot, I suppose you could always use a 2 or 3-position toggle to add 100k and perhaps something along the way, for low/med/high resonance.

[Kipper4]

Thanks Mark I'll try it with my perfboard version