[sdiy] Module Idea - re: EML 101

[jhaible at debitel.net]

> On AH there was a discussion about the sweepable filter response on an EML
> 101 to sweep from lp to bp to hp. I had an thought about it that would be
> more appropriate here:
> 
> This is a cool feature I haven't seen on other modulars. I checked out the
> schematic and it seems to be just a center tapped pot with lp bp and hp input
> on each lug. If it's that simple to sweep between responses that's something
> I'll have to try adding to a state variable filter.
> 
> This got me thinking about an idea though for a module or a also great add-on
> to a svf:
> What about a vc fader module (like the JH interpolating scanner)but with 3
> inputs to sweep through lp bp hp - plus if it was a seperate module you could
> do even more fun things like sweep vco waveforms sine to tri to square, etc -
> or even multiple vco's sweep different octaves... you get the point of the
> versatility. The interpolating scanner will do this but with 8 inputs. Has
> anyone designed a circuit for this for 3 inputs?

Yes, almost.
I've made a little scanner for exactly this application (SVF modes crossfade),
except that I added another input for a 4-pole-LPF.

http://jhaible.heim.at/tonline_stuff/hj_vcfsc.gif

If memory serves (it's been a while ...) I've even spaced the distance between
the modes differently, because you get a Notch mode halfway between LPF and 
HPF, and I wanted LPF, Notch, HPF, BPF, 4-pole-LPF evenly spaced. That means, 
twice the pot tracel between LPF and HPF compared to the travel between the
other modes. See front panel "Filter Mode":

http://jhaible.heim.at/tonline_stuff/jh4_front.gif

I don't remember the details, but I know it took my a lot of time to optimise
the function in Spice, using a handful of transistors only (instead of the
full blown opamp / transistor / diode method of the IS.)

JH.


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