VCF with inductors

[CGS2510.SEP.STUDENT.UCA at CUB.UCA.EDU]

> >A crossover in a speaker box uses inductors to define the cutoff frequency.
> >Is it feasable to use a transformer type arangement, that is an inductor with 
> >some extra turns around it, to form a variable inductance ? The extra turns 
> >would have a DC voltage applied accross them to give a electro-magnetic
> effect, 
> >and this DC voltage would be the control voltage?

> ...why yes, this is a saturable core reactance, as used in 
    power control
> systems a million years ago.....as the DC saturates the magnetic core the 
> inductance falls.....but you do not get the sort of ranges you want for
> most Emusic applications......
 
I can't wholeheartedly agree that you couldn't satisfactorily use 
saturable core reactors for audio purposes as I have never tried it.  
Now I will have to, thanks for the good idea.  In a typical well 
planned mag amp situation, you use several independant saturable core 
reactors with tons of control windings, a bias winding and often a 
feedback winding.  This gives you total control of the iron.  
Incredibly large gains are possible by doing this, like up to 
1,000,000 in some small signal military mag amps.  Usually, it is a 
power controller for lights or motors or something where the waveform 
doesn't so much matter, but the E.I power is important.  Of course you 
get some odd power factor also.  If you subjected a mag amp to a 
audio modulated tone, mag amped it and then sent this to a detector, 
I suspect it would make a reasonably intelligable signal amplifier.  
Having a high power version of high signal quality may be quite a 
challenge though.