[Re: [RE: VCDO]]

[Harry Bissell]

Harry Bissell: The CD4046 phase comparator two is edge sensitive and will lock
with zero phase shift (also a concern). The capture and lock range can be as
great as the VCO range. Loop filter (as you noted) is the "Gotcha". This was
used in the Boss Super Distortion and Feedbacker pedal.
Don't waste time with PLL.  Harry


Terry Michaels <104065.2340 at compuserve.com> wrote:
Message text written by Gene Zumchak
>Guys,

    I have another idea, and there is probably somebody that can implement
it.  Use
a simple voltage controlled high frequency oscillator and divide it down by
the
number of samples you want to have per waveform, say 64.  Use a
phase-locked loop to
lock the 64 times oscillator to the audio frequency you want to create. 
The audio
frequency is taken from an audio exponential front-end VCO.  The result
will have
the same accuracy and stability of the your audio VCO.  The audio VCO is
not
intended to generate tones, just a square wave for phase locking and can be
consequently as simple as possible.  Any comments?

Gene Z (the other Gene)
<

An interesting idea, one problem you might have is the fact that the VCO in
a phase locked loop can lock on a harmonic when you try to cover a
frequency range greater than one octave.  It might be possible to pre-tune
the high frequency oscillator with the control voltage driving the audio
VCO, and just use the phase lock loop to do a narrow range correction to
ensure tracking.  That gets around the false lock problem.

Another possible concern is lock up time, you might end up with a permanent
portamento.  If the loop damping is not critically damped, step changes in
frequency might briefly slew past the desired pitch.

This all sounds familiar, maybe it was already discussed some time back.

Terry Michaels


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