[sdiy] 3280 VCA question

[Kenneth Martinez]

I was breadboarding a 3280 VCA, copied from the final voice VCA of the
Prophet-5...see this link, top right of the page:

http://aupe.phys.andrews.edu/diy_archive/manuals/sequential/prophet5/p5_03_17.gif

I've got it working, but I don't understand the function of Q410 in controlling
Iabc - what does it do, since its base is connected to ground?  How does this
resistor-transistor-resistor setup differ from just connecting a single
resistor?