[sdiy] Jürgen Haible living VCO core

[Liam Wall]

Hi Neil, Thanks for your help here.

> "Franco Compensation".  At higher charging currents the resistor
> introduces a voltage into the feedback loop, which also appears on the
> output, causing the comparator to trigger earlier than it would
> otherwise, and so causing the oscillator to run slightly faster.  It
> is to compensate for the finite capacitor discharge time.

OK, great, I think I get this. Also "Franco Compensation" yields some
google results for further reading.

> > 2. What is the purpose of D15?
>
> Think about what could happen when power is first applied to the op-amp.

I guess it could spike negative momentarily, so this limits it to
around -0.7V, and is protection for.. Q3?