How the $@#! does the Moog ladder filter do what it does?

[tomg]

On 18-Jul-98, J. L. wrote:
>Hi, everybody...I've been reading the list for a month or so, but
>haven't had a question until now.

>I've spent some time looking at the schematic for ther Minimoog ladder
>filter from the DIY archive, but I'm having lots of difficulty
>understanding it...could someone please enlighten me about its function?

The voltage drive connected to the base of the emitter transistor causes a
collector current proportional to the exponentiated value of the base voltage
with a scale factor of about 18mv per octive. The collector current is applied
to the transistor ladder. The lower pair of transistor split the the current
into equal parts when no audio is present. When audio is present the standand
current is modulated inversly. As current increases the collector impedance
decreases providing a higher cufoff freq.

Liberated and condensed from the Taurus SM.

-Tom