[sdiy] How does the JX3P VCA work?

[Gordon JC Pearce]

I was looking at simple VCA circuits (I want popless muting for some communications gear, so a slightly ramped VCA would do but distortion isn't a big problem), and ran across this:

http://urekarm.tripod.com/synth/jx_vca.pdf

How exactly does it work?  I would have thought that increasing the CV would turn on both the pass transistor and the shunt transistor.  There's obviously something clever that I'm missing.

-- 
Gordonjcp MM0YEQ