[sdiy] TomG's 9v diode ladder VCF

[tomg@efm]

oops....I just did a quick breadboard...too much res....change
the feedback resistor on the res opamp from 47K to 2K2 or
just remove the 10K resistor from the inverting input to gnd.

Tom



> Try this version....You could say I made it for Ben but everybody
> should enjoy this one...it's dead simple!
> http://groups.yahoo.com/group/EFM_Synth/files/cookbook/vcf6se-sd.gif
>
> Untested 2x2" DIY layout....but confidence is high! Somebody do it up
> real quick so Ben will know it works.....
> http://groups.yahoo.com/group/EFM_Synth/files/cookbook/vcf6se-pc.gif
>
> It's 2 ics 12 diodes and 1 dual-npn (or matched 3904s) 16 resistors
> and 3 caps.....good luck..
>
> Tom
>
>
>
>
> > OK I'll do the hacks!  I tested it with random selected
> > 1N4148 diodes.
> >
> > I too prefer the Transistor Ladder... but the diode ladder is
> > nice too. I've heard that the differences are mainly to be found
> > in advanced mathematics that hurts my head...
> >
> > In simple terms (as I understand it...) The Transistor ladder
> > sections are better separated... the diode sections load each other
> > more due to the lack of gain in the diodes. So the 24db filter starts to
> > look more like 18db or so at some ladder currents.
> >
> > One place to get some matching is the capacitors... I'm using 2% in
> > both filters.
> >
> > Anyone know about the difference between the original MiniMoog ladder
> > (with the 150 ohm bias resistors) and the newer model (with the 1K
> > bias resistors ???)
> >
> > H^) harry
> >
> >
> > >From: DCMagnuson at aol.com
> > >To: Plutonique9 at symbiocom.com, synth-diy at node12b53.a2000.nl
> > >Subject: Re: [sdiy] TomG's 9v diode ladder VCF
> > >Date: Thu, 12 Apr 2001 11:22:43 EDT
> > >
> > >In a message dated 4/12/01 10:51:00 AM Eastern Daylight Time,
> > >paia2720 at hotmail.com writes:
> > >
> > > > You might want to consider a chip like the MAD1108 which has 8
diodes
> > > >  in it. Diode PAIRS need to be matched... not the diodes in one
"leg"
> > > >
> > > >  TomG's pc board for the diode ladder filter is not layed out this
> way.
> > >I'm
> > > >  gonna hack it to be "improved" one day... but it works OK without
> > > >  any matching as well...
> > >
> > >I have one of Tom G's VCF-6's, and I used no diode matching at all (I
> used
> > >1N914's) .  The filter sounds good to my ears, but I don't have a
matched
> > >VCF
> > >to compare it to.
> > >
> > >That said, I still prefer the sound of my 3046-based transistor ladder
> VCF.
> > >Does anyone know if the lack of diode matching could be the reason?
IE:
> > >what
> > >will the effects be because I did not match my diodes?
> > >
> > >Dave Magnuson
> >
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