[sdiy] New SSM2164-based Log/Linear VCA design

[David G. Dixon]

Further to my last post, I forgot to mention that the log/linear switching
scheme is a little bit different (and a fair bit simpler) than Gallo's as
well, largely because of the different way of handling the reference offset
voltage.  I will be using a simple panel-mounted DPDT On-On mini-toggle
switch (no on-board relays or analog switches).  Only the feedback loop of
the CV summer is involved in switching circuit -- no audio signals go
through the switch, so no worries!