[sdiy] Sallen Key with input mixing to generate all shapes

Andrew Simper andy at cytomic.com
Tue Dec 23 03:40:08 CET 2014

Hi David,

Can you please email them to me? I would love to see your design!

Also if you want help with setting up a web page please let me know,
you can get free hosting from many providers. Even just adding the
files to dropbox / google drive and linking to the folder in an email
here to the list would be fantastic, and that is pretty minimal in
terms of work at your end. It would be such a shame if you have
designs to share but aren't doing so because you "don't have a
website"!!! We can do better than this.

I just remembered doesn't this email list have a web page you could
create an account at and post content to? http://www.synthdiy.com/


-- cytomic -- sound music software --

On 22 December 2014 at 14:07, David G Dixon <dixon at mail.ubc.ca> wrote:
> Hi Andrew,
> I haven't published any schematics, because I don't have a website.
> However, anyone who buys a Korgo II PCB from me gets the schematic and the
> theory behind it.
> Cheers,
> Dave
>> -----Original Message-----
>> From: Andrew Simper [mailto:andy at cytomic.com]
>> Sent: Sunday, December 21, 2014 7:35 PM
>> To: David G Dixon
>> Cc: synthdiy diy
>> Subject: Re: [sdiy] Sallen Key with input mixing to generate
>> all shapes
>> Hi David,
>> Yes you're quite right, there is no need to stick the same
>> input signal at each input mixer, you can filter any signal
>> you want. I hope I haven't lost you any commercial advantage
>> by outlining the theory of operation, but I can assure you I
>> developed it independently. Have you published any schematics
>> or other documents on it yourself? I haven't seen anything in
>> all my searches.
>> All the best,
>> Andy
>> -- cytomic -- sound music software --
>> On 22 December 2014 at 08:52, David G Dixon <dixon at mail.ubc.ca> wrote:
>> >> This very concept is the basis behind the Intellijel
>> Korgasmatron II,
>> >> which (with the expander) allows one to derive different responses
>> >> from the same filter simultaneously.  The only difference
>> is, in that
>> >> case, the topology is that of the MS-20 2-pole filter.
>> >
>> > I wanted to clarify what I wrote before, and add that one can get
>> > different responses from different inputs to the Korgasmatron II.
>> > Hence, one audio signal can be lowpass filtered, a second
>> audio signal
>> > can be bandpass filtered, and a third can be notch filtered, all at
>> > the same time, all by the same filter.  I don't know of any other
>> > commercially available filter which is capable of this
>> (although most
>> > filters are capable of this, I believe, if set up properly).  This
>> > trick has some interesting uses.  For example, if one audio
>> signal is
>> > lowpass filtered, and another is highpass filtered, then
>> sweeping the
>> > cutoff makes one disappear and the other appear at the
>> output.  If a
>> > third audio input is bandpass filtered at significant Q, then this
>> > acts almost like an interpolating scanner, bit with more
>> interesting sound.
>> >

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