[sdiy] Leapfrog (was: Re: Cauer Filter Design)

[jhaible]

> > >I would however consider doing a ortonormal leapfrog
> > >ladder.
[...]
> > The only thing that worries me about this idea however is the number
op-amps
> > needed per section.

On a slightly related topic:

I have tried to work out a leapfrog filter design for the 25-inductor
Hammond
Line Box. This means 50 or even 75 opamps. (Yes, the long version of the
Hammond line box is a 50-pole low pass filter!)

This was my first encounter with leapfrog circuits. After getting over the
initial
problems, it's not that difficult at all, especially for a LC circuit with
many
equal stages. And I learned that the good old State Variable filter is
nothing
but the "leapfrog" method applied to a single LC circuit - or the other way
round,
leapfrog design means applying the "state variable" method to more complex
RLC circuits.

Anyway, while it was interesting to read about this and do a little
excercise
on paper, I still hesitate to build a circuit where the signal would run
thru
50 or even 75 opamps. Not sure how the ever so tiny unwanted side effects
of an opamp will add up in a long signal chain. For *that* application, I
guess
it's easier to just use 25 cheap inductors.

But as I said, this is more of a _question_ (and doubt) than a statement.
Has
anybody else on th elist practical experience with "long" leapfrog designs?

JH.