[sdiy] VC Sallen-Key with a 2164

Jacob Watters jacobwatters at gmail.com
Wed Apr 27 05:38:14 CEST 2016


The Monotron has an MS20 filter with virtual ground.

However, you should really consider a dual rail power supply.

On Tuesday, 26 April 2016, Andrew Simper <andy at cytomic.com> wrote:

> PS: the first stage in Olivier's circuit optionally switches out the
> first capacitor, which is what the Oberheim XPander did. This is the
> take weighted sums of the 4 output stages to generate different
> responses, so just leave that cap in the circuit like the other stages
> for what I propose.
>
> On 27 April 2016 at 10:48, Andrew Simper <andy at cytomic.com <javascript:;>>
> wrote:
> > Hi Pru,
> >
> > There is no way to build an MS20 type structure with virtual grounds,
> > but there is another structure I came up with independently and have
> > called SMP in my software. The equations are:
> >
> > 0 = g (v0 - v1 + k (v1 - v2)) - s C (v1 - 0)
> > 0 = g (v1 - v2) - s C (v2 - 0)
> >
> > but because each stage has an inverting op-amp virtual ground buffer
> > this turns into:
> >
> > 0 = g (v0 - v1 + k (v1 + v2)) - s C (v1 - 0)
> > 0 = g (-v1 - v2) - s C (v2 - 0)
> >
> > where g is the cutoff gain, k is the resonance gain (from 0 to 2), and
> > C is the value of the capacitor, which in turn alters how much g needs
> > to be.
> >
> > Olivier has done a 4 pole cascade using 2164, so the setup is similar
> > but you just need the first two one pole low pass stages, but the
> > resonance path becomes the sum of the first and second stage outputs
> > (which is actually the difference because of the inverting buffers),
> > gained up by the resonance amount, limited in some way, and fed back
> > to the first stage input:
> >
> >
> http://mutable-instruments.net/static/schematics/Shruthi-Analog-PoleMixing-v02.pdf
> >
> > All the best,
> >
> > Andrew Simper
> >
> >
> > On 27 April 2016 at 08:53, prudence prendergast
> > <prudence.prendergast at gmail.com <javascript:;>> wrote:
> >> long time, first time.
> >>
> >> i was hoping for some advice. is there a way to build a VC sallen-key
> >> low pass filter with a 2164? since 2164s require a virtual ground at
> >> the output, the matter seems complex.
> >>
> >> i think dave dixon might have written an article on feeding true
> >> buffers with the 2164, if he's here to weight in.
> >>
> >> -pru
> >> _______________________________________________
> >> Synth-diy mailing list
> >> Synth-diy at synth-diy.org <javascript:;>
> >> http://synth-diy.org/mailman/listinfo/synth-diy
> _______________________________________________
> Synth-diy mailing list
> Synth-diy at synth-diy.org <javascript:;>
> http://synth-diy.org/mailman/listinfo/synth-diy
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://synth-diy.org/pipermail/synth-diy/attachments/20160426/a32bf9e9/attachment.html>


More information about the Synth-diy mailing list