butter and pole locations

[Tom May]

Don Tillman writes:

   The generalized version (any values for the Rs and Cs) is too long for
   me to conveniently write out, but if you set all the Rs equal and all
   the Cs equal, the transfer function becomes:

     Vout              1
     ---- = ----------------------------
      Vin   s^4 + 7s^3 + 15s^2 + 10s + 1

   (I *think* this is correct.  If anybody cares they can do it out
   independently and we'll compare notes.)

Curiously enough, I had just copied the Moog ladder filter patent at
the library this morning so I just learned how these things work.  I'm
assuming the diode ladder is similar, just replace the transistors
with diodes and drop the resistive ladder supplying the bias voltages.
Yep, the TB-303 circuit on Hyperreal looks pretty much like I would
expect.  Hmm, using diodes seems a lot more elegant.

So the small signal circuit for a fixed control voltage would look
like this, right?  Hardly the "all 4 poles the same" circuit that I
had been led to believe it was!

+--R--+--R--+--R--+--R--+---
|     |     |     |     |
Vin   C     C     C     C  Vout
|     |     |     |     |
+-----+-----+-----+-----+---

It must, because I get the same Vout/Vin as you(!).  And those poles
are really sprayed all over the place.

Tom.