[sdiy] Yves Usson's Minimoog Filter

[jarno.verhoeven]

Hello Dave,Ihad pretty good luck with ladderfilters ,I suppose :-)I've used 2N3904 for a Taurus vcf+vca, and I believe BC547 in a minimoog vcf+vca clone.For both of the builds I did, I matched both pairs of transistors across, but also matched the caps. It might be that they did not have to match the caps at the time, since they could simply buy them with a tight tolerance, but thats a bit harder these days.As others have mentioned, the vca is a big part of the sound as well. I built mine of the schematic by Marjan Urekar, so not quite adjusted to eurorack signal levels, it distorts REALLY nicely! I have used an attenuator in front to dial it back. And, I changed the order, as they are two sequential vca's. Footpedal in one, actual envelope in the other, not sure which one is first in mine, footpedal input is simply a pot.Sent from my Galaxy
-------- Original message --------From: David G Dixon via Synth-diy <synth-diy at synth-diy.org> Date: 10/06/2023  06:11  (GMT+01:00) To: synth-diy at synth-diy.org Subject: [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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