[sdiy] Capacitors in Moog ladder filter

[Czech Martin]

It was stated several times on this list, that different
capcitor sizes will lead to different dc bias of the ladder,
if tuned to the same frequency.

Since the ladder and diff amp at the top will behave nonlinear
for large signals, this can make a difference.

m.c.

> -----Original Message-----
> From: owner-synth-diy at dropmix.xs4all.nl
> [mailto:owner-synth-diy at dropmix.xs4all.nl]On Behalf Of Tim Heffield
> Sent: Montag, 26. April 2004 18:40
> To: Synth-Diy
> Subject: RE: [sdiy] Capacitors in Moog ladder filter
> 
> 
> Hello Yves,
> 
> Thanks for the information.  I think I will stick to using the 0.022uF
> (22nF) as well.  I was just wondering if there were other 
> things to be aware
> of.  By the way I breadboarded the Steiner filter last night 
> and was very
> impressed with it's performance.
> 
> Regards,
> 
> Tim
> 
> -----Original Message-----
> From: Yves Usson [mailto:yves.usson at imag.fr]
> Sent: Monday, April 26, 2004 3:31 AM
> To: Tim Heffield
> Subject: Re: [sdiy] Capacitors in Moog ladder filter
> 
> 
> Hi
> 
> you are right ! The value of the ladder caps is responsible for the
> frequency range. Personally I use 22nF caps for my ladder filters,
> this gives an evenly distributed range (10Hz up to 22 000Hz).
> If you use 100nF caps as in EFM designs you will lower the 
> range toward
> the bass
> and the upper limit won't go higher than 8 000 Hz. As a matter of fact
> Moog used 100nF in his Taurus Bass Synth.
> As far as I am concerned I used 22nF caps for the VCF1 of the EFM
> Wildcat and
> for the VCF2F.
> 
> Cheers
> 
> 
> 
> > I have a question about the four caps in the Moog ladder filter.
> > Looking
> > through all my old documents and on the web I see values that range
> > from
> > 0.022uF to 0.1uF for the the four caps that create the poles.  It
> > seems to
> > me that this would just raise or lower the resonant freq for a given
> > CV.
> > Does anyone know if there is more to it than this?  I 
> noticed that the
> > Mini-Moog filter started out with 0.068uF and someone changed it to
> > 0.027uF...was the cutoff frequency to low?  EFM seems to 
> use 0.1uF on
> > all of
> > his filters.
> >
> > Tim
> >
> >
> -------------------------------------------------------------
> Yves Usson
> 
> Lab. TIMC UMR5525 CNRS
> Institut d'Ingéniérie et de l'Information de Santé (IN3S)
> Faculté de Médecine
> Domaine de la Merci
> 38706 La Tronche cedex
> 
> email : yves.usson at imag.fr, yves.usson at ujf-grenoble.fr
> 
> tel.  (+33) (0)456 520 074
> fax.  (+33) (0)456 520 022
> 
> 
> 
>