[sdiy] TomG's 9v diode ladder VCF

[Happy Harry]

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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