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

[David G. Dixon]

> This design, of course, is very similar to the old Electronotes design of
> Bernie Hutchins.  I worked for many years improving and tweaking the
> design, since it was being used at ultrasonic frequencies (the original
> DoubleDekka) and needed to track up to ~80 kHz.
> 
> As part of my work on this circuit I discovered the rather surprising fact
> that a fast opamp outperformed the discrete Schmitt trigger!  I used the
> then new LM318, which is still available, inexpensive and fast (70 V/us
> slew rate). It would be very interesting which method does better in
> simulations, since using an opamp is quite a simplification.

Yes, I've been reading about the LM318.  Hal Chamberlin recommended it for
sample and hold circuits.  I think I might give that a go, at least in
simulation, and get back to you.  I'm not all that impressed with the
symmetry of the discrete ST output, either, although it doesn't really
matter since all it does is saturate the OTA in the VCO-1.