[sdiy] Yves Usson's Minimoog Filter

Rutger Vlek rutgervlek at gmail.com
Sat Jun 10 19:19:45 CEST 2023

Hi David,

Here are some thoughts your original post triggered. They may or may not be

1. I recall reading about some manufacturer of ladder filters clones,
explaining how they deliberately did not match all transistor pairs in the
ladder. I vaguely recall only the first (and perhaps last) pairs were
matched... With the rationale that things became to sterile with everything
tightly matched.
2. As others have said: input level plays a crucial role
3. What is your personal reference for the Moog ladder sound? Could it be
one of the more recent bass-compensated versions?
4. The VCA into which the VCF feeds, also plays a role in the sound of the
Minimoog. Could that be what you're missing?



Op za 10 jun. 2023 15:04 schreef Jean-Pierre Desrochers <jpdesroc at oricom.ca

> In 2016 I built a Moog 904A VCLPF clone
> from Moog’s modular original schematics.
> I’m VERY happy about the resulting behaviour of it.
> Very fatty and precise sound !
> I used matched pairs of BC550C NPN’s for the ladder job.
> I supposed the 904A VCF design is very close to the one the minimoog uses..
> Anyway, all my projects files are open source for anybody..
> http://www.arcenson.com/projects/Modular/M104A_Lowpass_Filter_Moog_904A_clone/Specifications/M104A_VCLPF_schematic.pdf
> *De :* Synth-diy <synth-diy-bounces at synth-diy.org> *De la part de* David
> G Dixon via Synth-diy
> *Envoyé :* 10 juin 2023 00:09
> *À :* synth-diy at synth-diy.org
> *Objet :* [sdiy] Yves Usson's Minimoog Filter
> Hello SDIY Team,
> I've built a ladder filter on my own PCB layout from Yves Usson's Minimoog
> ladder filter schematic, and I must confess that the results are less than
> stellar.  The filter works, but not terribly well, and it sounds nothing
> like a Minimoog.  I used 2N3904 and 2N3906 instead of BC547 and BC557, but
> I matched all of the transistor pairs in the ladder, and matched the four
> transistors at the top and bottom of the ladder as well as the other four
> transistors, using Ian Fritz's transistor matching circuit (which I also
> laid out and built on a PCB).  I did not try to match the one PNP to the
> current driving NPN below the bottom of the ladder.
> Does anyone here have any experience with this schematic?  Will it change
> anything if I replace the 3904s with 547s, etc?  Everything else was
> exactly as specified in the schematic.  This was my second attempt to build
> from an Yves Usson ladder filter schematic.  My "Raging Bull" Taurus filter
> didn't work at all.
> I just want to know if there is some fundamental flaw in this schematic
> before I spend too much more time with it.  Any insights would be most
> appreciated.
> Dave Dixon
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