[sdiy] Article "Analyzing the Moog Filter"

Michael E Caloroso mec.forumreader at gmail.com
Sat Aug 24 03:40:54 CEST 2019

The Colin/ARP SVF puts the integrating cap in the integrator following the

The Rossum/Oberheim SVF puts the integrating cap at the output of the OTA,
shunted to ground.

They both have pros and cons, and they sound different.

Then there's the ARP 4075 VCF based around the LM3900 Norton amplifier.
The first low distortion low noise high fidelity VCF.  I just read the
patent (US 4,011,466) on the 4075 and it is a fascinating read.  That's a
unique topology.

One thing the article fails to touch on is the feedback architecture.
Feedback has a big impact on the sound, and the feedback design changed
between Moog synth models.  That is why players back then complained that
the new models didn't sound like the Minimoog.  My post in SDIY way back in
1997 here:



On Fri, Aug 23, 2019 at 6:44 PM Donald Tillman <don at till.com> wrote:

> On Aug 23, 2019, at 2:23 PM, mskala at ansuz.sooke.bc.ca wrote:
> On Fri, 23 Aug 2019, Donald Tillman wrote:
> On Aug 23, 2019, at 9:09 AM, Quincas Moreira <quincas at gmail.com> wrote:
>      Don’t forget the Leapfrog topology as implemented by Matthew
>      Skala.
> I don't know it.  'Gotta schematic?
> https://files.northcoastsynthesis.com/msk-007.pdf  (page 69 of the PDF)
> (Very nice writeup!)
> Well, yeah... that's clearly an exception.  :-)
>   -- Don
> --
> Donald Tillman, Palo Alto, California
> http://www.till.com
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> Synth-diy mailing list
> Synth-diy at synth-diy.org
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