[sdiy] Yves Usson's Minimoog Filter

Jean-Pierre Desrochers jpdesroc at oricom.ca
Sat Jun 10 15:01:22 CEST 2023

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..




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


Dave Dixon

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