Is this stupid?

[Martin Czech]

> yknow, theoretically, I have often wondered the SAME thing!
> Not stupid at all..(well, if it is, then we are stupid in a group, which
> is always easier to swallow) :))
> rob
> 
> 
> Tony Allgood wrote:
> > 
> > Hi all,
> > 
> > This may be a stupid question but I'll ask it anyway. Has anyone ever tried
> > using inductors in a Moog ladder instead of the capacitors to make a VCHPF?
> > I guess you would need to put some cap in series with the Ls to block any
> > DC.
> > 
> > And secondly, has anyone found a need for taking a differential tap off the
> > ladder at another point other than below the top pair to create reduced
> > steepness of slope?
> > 
> > Regards,
> > 
> > Tony Allgood, Cumbria, UK
> > 
> > e-mail: oakley at enterprise.net
> 
> 
Part one:

I can't see any major problem in using inductors, just the problems
that inductors have: size,quality, cost, availability.  With no audio
signal, the dc potentials of the ladder should be the same for each
stage, so no problem to clamp these together with the inductor.  The
circuit might suffer from inductive hum, and the low frequencys might
not be damped as expected, because of nonzero resistance of the
inductor coils. And the feedback will not work any more (from my head),
I think the loop has to be attached to the other side of the diff.
signal input.

No , part two is not stupid but interesting.

Sometimes I would like to have the same cutoff point, but not such a
sharp decrease in brightness. So you need 6dB,12 dB and maybe 18dB,
too. I'd say there is a need, have a look at the formant 24dB filter.


If you have a high impedance diff.  buffer you can of course tap the
other 3 points in the ladder. Instead of using a (expensive) 2 way 4
position switch I'd rather build 4 output stages. But the resonance
loop should contain only the last 24dB tap, it is obvious that it won't
work as expected with the other 3 taps.  But it could be a nice
experiment to do this (via external feedback).