[sdiy] Buchla 295 weird topology

[Aaron Lanterman]

On Aug 23, 2009, at 12:52 AM, Donald Tillman wrote:

>> The pure lowpass and highpass sections are standard Sallen Keys
>> with an unbuffered first-order passive section slapped onto the
>> front. This turns it into a rather nonstandard Sallen
>> Key.
>
> Um, not exactly.  It's a third order Sallen Key.  The R and C up front
> are part of the circuit and interact with it.  So it's not just not an
> additional pole slapped on the front.  (The math on this gets
> significantly hairier.)

Oh, yeah, I know that - you can't analyze them as separate stages. I  
was just trying to visually describe what it looks like. I took  
several different approaches to analyzing it, all of which looked like  
they'd lead to all sorts of unpleasant algebra. So I was glad when I  
found Marshall's writeup. ;)

- Aaron