[sdiy] Newbie question: Diode ladders

[Colin f]

> > with an ohmmeter. The other point is that as the
> > diode forwant drop stays reasonably constant over a
> > really wide range of current, the equivalent
> > resistance can vary by many orders of magnitude.
> 
> The exactly same thing happens in transistor ladder filter. 
> The difference 
> is that stages are buffered from each other so the filter 
> behaves pretty 
> close to RC (for small signals that is).

One thing to note about the behaviour of the ladder filter is that the input
audio signal, although small compared to the DC current setting the centre
point of R in each stage, also has an effect on R and therefore Fc.
You can hear this quite clearly on a minimoog with resonance turned full up
and no other cutoff modulation than the audio input.
You can't hear it on the Arturia model of the minimoog filter ;-)

Cheers,
Colin f