I’ve updated the original post with version 2 of the stripboard layout.
This is the initial falling edge of the pulse:
This is before i got the values right:
(470k resistor, 1nf capacitor) = 0.00047s Time constant
This is the curve i settled with:
(1k resistor, 100nf capacitor) = 0.0001s Time constant
It would be nice if i could get the curve to fall off faster, but in my experimenting, it just messed with the signal too much. Listening to it, it sounds just fine. You could probably even skip this step.