[sdiy] They aren't sawtooths, they're ramps

[David G. Dixon]

Boy, am I ever stupid!  I designed, simulated, laid out and built a
Triangle-Core VCO based on the 2164 Expo, and then it didn't work.  Why not?
Because I forgot (for the second time!) that the 2164 must feed its current
to virtual ground.  I wired it directly to the Iabc of LM13700, which rides
at about -13.5V!

At least I've got a nice front panel, and I can reuse all the board parts
for a Saw-Core, so I'm really only out a bit of board material and a few
hours of wasted time, but still (urrggh!).

This all stems from the fact that there is no SPICE model for 2164 (Sam
Hoshuyama not withstanding), but it is easy enough to put the basic I-V
relationship for the VCA into SPICE.  This lulled me into a false sense of
security.

I'm completely fed up with this now, so work on the Triangle-Core 2164 Expo
VCO is officially cancelled.  The Saw-Core version will have to be good
enough (it's actually very nice).  I'm going to go to the garage and etch a
new Saw-Core board right now, and try to forget all about this whole sorry
episode!