[sdiy] C&K 7211

[Scott Stites]

Yep, I really lurv these switches - they came along just about the right
time for me.

I mentioned before I was building a dual version of Rene's 'Late MS-20'
Filter.  Just finished drilling the panel and building the PCB bracke.  I'm
configuring it so that, through switching jacks for the input, one input
will put it in the normal MS-20 series mode, one input will put it in
parallel mode (with an extra mixed output supplied for that), and the two
filters can also be used independently with independent outputs.

With Rene's filter, there's a point to inject for high pass that is normally
connected to ground.  A wonderfully weird BP response can be had by
injecting the signal to the 'normal' low pass and high pass input
simultaneously, so the switch is working pretty much like you described:

Position 1 injects the signal to the low pass.  Position two lifts the
ground and injects the signal to both high pass and low pass inputs, and
position three injects the signal only to the high pass input.  Each filter
will have it's own switch for this.

The third 7211 is used to allow the frequency controls to be conveniently
used for independent, series and parallel modes.  Position 1 sends each pot
voltage to each respective filter.  Position two mixes the first filter's
pot voltage with the second filter's frequency pot voltage, which allows the
first filter's pot to move each filter in tandem while allowing the second
filter's freq pot to set an offset - so an offset can be set between the two
filter's cutoff frequency.  The third position sends the second pot's
voltage to the inverting input of the first pot's CV mixer, so the first pot
will still move the two filters in tandem, but the second pot will spread
the two CV's out - like a bandwidth or bandspread control.  This is useful
when in the series mode, and the first filter is set to HP and the second
filter is set to LP.

I'm starting to view circuits now on the basis of "Is it 7211-worthy?" or
"Is it CA3080-worthy?".  =-D.

Cheers,
Scott, who obviously has watched too much "Seinfeld"




----- Original Message -----
From: "harrybissell" <harrybissell at prodigy.net>
To: <synth-diy at dropmix.xs4all.nl>
Sent: Tuesday, October 19, 2004 11:02 PM
Subject: [sdiy] C&K 7211


> Another interesting use of the on-on-on switch... that I forgot
> to mention... is that you can use it to send signals to one, another,
> or BOTH destinations.   Think of perhaps a modulation signal, with
> an attenuation pot...that couldsend the signal to the VCO, VCF, or
> BOTH at the same time.
>
> even more complex circuits are possible... I have used them in
> oscillator sync and mod circuits
>
> possibilities are endless...
>
> H^) harry
>