PLL ... Thanks, Don Tillman

[Scott Gravenhorst, Synthaholic]

First, I got it working.  The over/undershoot is down to a chirp for 
small pitch changes.  Kinda wild sounding, very interesting.  Makes a 
nice perfect 5th.

Here's what happened:

I found a fine print notation in the MC14046 (4046) spec sheet 
regarding design math... 'component value calculations could be off by 
a factor of *four*'.  Oh.

I needed a larger PLO timing capacitor (it was falling out of lock at 
the low end of the keyboard), and thanks to Don T. I hit the filter 
hard.  It wanted a low pass like this:

   >------\/\/\/\------+-------\/\/\/\------->
            R1         |          R2
                    -------
                    -------
                       |
                       /
                       \
                       /  R3
                       \
                       /
                       |
                       |
                    --------
                   /   /   /

R1=R2 and R3 = .1 * ( R1 + R2 )

I started with a simple R and C filter.  It gave too much over/under 
shoot.  The spec sheet said the above filter design would be close to 
optimum.  The nice thing is that I can bring some of the components out 
to the front panel to control lock range and the presence and timing of 
the chirp effect.

Is there any interest out there in the final design drawing for this?  
Let me know and I will post it to synth-diy.

-- Scott


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