[sdiy] Multi-Input filters

[harrybissell]

er... I'll try the "how saturated transistors work as variable resistances"
at the risk of blowing it and sounding stupid.

With the transistor 'around' saturation... Vce is nearly constant (and for
small AC
signals this stays true)...and the current is a strong function of the
base-emitter
current.

So we can vary the collector-emitter current by varying the base-emitter
current.

With different collector-emitter currents... the voltage remains reasonably
constant...
so plug in ohms law, and it tells you the resistance must be changing.

This IS the case for all the diode type transconductors where we vary
standing current
and voltage changes only slightly. I presume my explanation expands on this
idea... or I'm
full of sh!t. whaddya think ???

H^) harry

jhaible wrote:

> > I'd suggest you to check (translate) this Japanese site
> > first.
> >
> > List of topologies and devices for VCFs:
> >
> >   http://www.asahi-net.or.jp/~wz4k-tnk/kairo/vcf3.html
> >
> > I can't find errors easily.
> >
> > In this Mr. Tanaka's site, some explanations about VCFs
> > are updated.  Theories of Korg35 style filter and the
> > transistor ladder filter are added last year.  There
> > may be some other additional updates.
> >
> >   http://www.asahi-net.or.jp/~wz4k-tnk/kairo/vcf.html
> >
>
> Awsome web site indeed!
> This gave me inspiration for my JH-720 project, and the PS-3200
> clone would not have been able without it either.
>
> Theory of Korg35 filter: I just saw there is some new (Japanese)
> text, referring to voltages and currents in a drawing of the 2-transistor
> core.
>
> Sam, as you're speaking Japanese and I'm not: Is there new information
> about how this actually works? (Of course the transistors act as VC
> resistors, but *how* they do this is still beyond me, and beyond
> every industrial analog ASIC designer I've asked so far. )
>
> Best Regards,
>
> JH.