Commutating Filter (was "Stacked Power Supplies...")

[Stopp,Gene]

The switching frequency is controlled by an ultrasonic VCO (I think I
used a 4046). I provided sweep inputs (naturally!). The analog switches
are 4051's.

 - Gene

 ----------
From: Magnus Danielson
To: gene.stopp at telematics.com
Cc: synth-diy at mailhost.bpa.nl
Subject: Re: "Stacked" Power Supplies - any thoughts?
Date: Tuesday, May 19, 1998 6:25PM

>>>>> "S" == Stopp,Gene  <gene.stopp at telematics.com> writes:

 S> Regarding the commutating filter, I intend to find out what it
sounds
 S> like! I did test it out when I built it in the lab back at my old
job
 S> (lots of spare time right before we closed the doors on the place)
but
 S> it was listening to a sawtooth wave from an HP function generator
into
 S> the gizmo over headphones. I remember the impression that I got was
very
 S> flanger-like. But I reeeeally want to see what it sounds like with a
few
 S> VCO's into it, and maybe some nice crisp white noise. You may
remember
 S> that it basically consists of a pair of switched-cap integrators in
a
 S> state-variable configuration, with a dual pot where the two
integrator
 S> R's  would normally go and labelled "Bandwidth", plus a Q
control....

What switching frequency?

Can you modulate the switching frequency?

When the switching frequency is well above your signals bandwidth (and
ears ;) then this would act very similar to the digital IIR
filters. They will need the Z-transform to analys correctly (I have
several references to this if someone is die-hard on theory) and they
will certainly follow a diffrent filter-function than normal
state-variables do. You will even find that it's high-end properties
is quite obstructed as compared to the normal state variabler filter,
this is of course due to the wrapping of the jw axis into a circle!

If you can modulate the switching frequency, possibly PWM it you can
get some possibly interesting effects. If you run the frequency down
in the audio range you get a nice wrapping effect which effectively
act as a waveshaper (and a VERY unlinear one).

I can also imagine that some of the above effects would be about the
lamest thing that happend - "Look, we just got ourself an additional
DC term!" or similar... experimentation will show...

Did you use CMOS switches for this one?

 S> I hope it's weird.

Jaaa, I bet'ya! (In that funny "Fargo" way).