[sdiy] 4-Quadrant VCA?

[Tim Ressel]

Hey y'all,

I am making a voltage controlled bipolar mixer, so I need a bipolar i.e. 
4-quadrant VCA. So 2 channels mixing together with bipolar voltage 
control. Here is what I am thinking:
*http://www.synthdiy.eu/files/BipolarVCA.png*
A rectifier circuit will drive the 13700 Iabc port and a comparator will 
drive the switch.

I know I could use AD633s but they are really pricey. Any other clever 
ways of pulling this off?
**

-- 
--Tim Ressel
Circuit Abbey
timr at circuitabbey.com

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