[sdiy] Yves Usson's Minimoog Filter

Quincas Moreira quincas at gmail.com
Sat Jun 10 10:31:17 CEST 2023


Here’s my build for reference, hope it helps
https://vimeo.com/63276268?share=copy
This one has an ab comparison with the real moog

https://youtu.be/XCtEGAGYbx0


Cheers


Quincas

On Sat 10 Jun 2023 at 1:41 Ben Bradley via Synth-diy <
synth-diy at synth-diy.org> wrote:

> I have two thoughts. First is the schematic says (at each transistor)
> BC547C, with the C suffix indicating higher HFE. The Onsemi/Fairchild
> datasheet shows the C grade to have Hfe of 420 to 800. From my study
> of the Moog filter, the original "special" TIS97 transistors had a HFE
> of around 800. This is higher than the average 2n3904, but not WAY
> higher, so I don't know if it would make a significant difference.
> I've wanted to make this kind of filter with transistor sockets so I
> could easily find out, especially if there's really any magic related
> to the "special" transistors as some have claimed.
>
> The other thought is the input signal level. I recall part of the
> filter's sound has to do with the input being slightly or moderately
> overdriven (with the Minimoog mixer level at full volume), so try
> increasing the input level until the tone changes, and see if that's
> more to your liking.
>
> On Sat, 10 Jun 2023 at 00:12, David G Dixon via Synth-diy
> <synth-diy at synth-diy.org> wrote:
> >
> > 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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-- 
[image: QMA]

Quincas Moreira
Director | QMA
mobile:  5534988825
site:  quincasmoreira.com
email:  quincas at gmail.com
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