[sdiy] Ripples Schematic (forked from 4-pole BPF thread)

[Olivier Gillet]

> Olivier, I have a couple of questions about the Ripples schematic you just posted here. (thanks, btw!)
>
> What is the purpose of the PTCs on the rails? I was not aware of what they did, looked it up, makes sense of course. Are they just here for protection?
>
> And what is the purpose of the schottkys near the power connector?

If polarity is reversed by accident, the two schottky diodes are
conducting and directing all the current away from the circuitry. The
amount of current circulating through the polyfuse is such that it
trips.

The "bonus" effect of the schottky is that it protects the V2164 from
a missing negative supply.

Another protection scheme is to use diodes in series with the power
connector. But then you get a voltage drop (and no 2164 protection).

> Aaand using lm13700s for the extra vcas is pretty dang "duh". For some reason I'm usually thinking "either/or" when it comes to 2164s and OTAs. Silly me!

I use the LM13700 for voltage-controlled resonance in cascades because:
* Differential inputs are very useful here for the resonance
compensation trick (this saves one or two op-amps).
* It provides the non-linear element that tames down self-oscillation
to a very clean sine.

And with one half used for voltage-controlled resonance, it was a no
brainer to use the other half for a VCA!

I've built a "no OTA" 2164 4-pole (2x extra 2164 cells for linear VC
resonance) but did not like it as much as that one.

Olivier