[sdiy] I've made a VCO... On accident...

[harrybissell]

My guess would be that you have put positive feedback around the filter,
with
a positive gain.  Somewhere the filter is limiting, probably where you
have the
square wave.

It is a valid way to make a VCO. Its not cheap, or easy so most don't
use this
method.

If you figure out where the feedback is, and limit the amplitude so that
you do not
clip at that point, you will be on your way to discovering a quadrature
sinewave
oscillator.   The triangle wave you saw will become more sinuoidal (but
not perfect)

H^) harry

Jeff Farr wrote:

> While preparing the circuit from an Electronotes filter (VCF1) I was
> moving around some of the jumper wires to twiddle with output
> schemes.  Now, I'm not exactly sure what caused the transformation as
> I havn't replicated it yet, but the circuit began acting like a rather
> nice VCO, the  summer showed a nice square, the first integrator
> showed a nice triangle and the second integrator showed a nice sine.
> All responded nicely to CV, with no DC drift or other problems I had
> to work out of the circuit as a VCF.  Needless to say I became rather
> excited about the prospect of having a module that could switch
> between 2-pole filter, VCO, and VC-LFO duty (I measured a wide
> frequency range while it was working).  Anyone have expirience with
> this?