[sdiy] TZ triangle core

[Ian Fritz]

OK, I had the topology out of order.  This one is what works:

Lin CV --> polarity switch 1 --> integrator --> polarity switch 2 
-->  Schmidt triggger
Schmidt trigger  --> polarity switch 1 control
Lin CV --> comparator --> polarity switch 2 control

Still just 6 opamps and an OTA.  Has anyone seen one simpler?

Still a minor issue with startup for one modulation polarity, but turning 
the know over to the other side gets it going.  It may need a little 
kickstart something or other.

   Ian