[sdiy] Zener clipping Was : ...that 1K resistor on the output

[David G. Dixon]

> So I guess this is an improved version of the ENS-76 Option 2 VCO (EN#75,
> p11)?  That used an OTA hysteretic switch driving a  4-diode clipper
> (+/-1.2V) followed by an attenuator to +/-50mV to drive the OTA
> integrator.  Has anybody tried that one?

No, I haven't tried it, but it's similar in principle, insofar as it uses a
hysteretic switch.  However, how the switch is driven is different.  In the
ENS-76 circuit, the clamped comparator output is taken directly back to the
+ comparator input, and the triangle is taken to the - input.  This is
elegant and effective, but I'm not sure how you'd apply sync to it.  In
mine, the triangle and the clamped comparator output are summed into the +
input of the comparator, and the - input is grounded.  This is easy to sync,
even variably -- just put spikes on the "grounded" - comparator input.  You
can also bring out the signal from the + comparator input through a buffer,
which gives an interesting waveform which I'm calling "zigzag".

Of course, the main difference is that the ENS circuit is based on the
classic overdriven OTA approach, and mine is based on the 2164 VCA.  This
creates many new and exciting possibilities for linear FM, on which I will
elaborate in more detail in a future post.