[sdiy] Phase-locked loops and the root of my headache

[Scott Gravenhorst]

grichter at asapnet.net wrote:
>
>> Not usually, but who knows what wierdness can be invented.
>
>Here a good example of invented Wiardness, the #3 Standard Wogglebug
>
>http://www.musicsynthesizer.com/WoggleBug/WoggleBug.html
>
>> 
>> mmmm, I think the answer is yes.  As long as the input signal's
>> frequency is within the limits of the lock range, the PLL's VCO
>> will follow it around like a puppy dog.
>
>But the response is slew rate limited, i.e. permanent portamento. Also
>damping of the step response is critical. The Wogglebug is a deliberately
>badly built PLL with the underdamped step response used as a tone and CV
>source.

(c:  My circuit has adjustable damping, adjustable VCO range, and
an LFO input.
With proper adjustment, I can make the portamento so fast that it
is barely perceptable at all.  PLL's get a bad rap, but my experience
is that 1) they don't deserve it. 2) you can adjust the heck out of
them. 3) why do so many people look at this underdamp/overdamp
issue as a drawback?  It's a FEATURE.  You can do some neat things
to the attack portion of a sound with a PLL.  I love mine, it outputs
7 signals at 12F, 6F, 4F, 3F, 2F, 1.5F and 1F into a little
mixer.  I can dial up different harmonic structures with it.
One day, I'd like to replace the mixer with a bank of 7 VCAs.
I have an old (but functional) 6800 microcomputer that I could
use as the brains for a 7 channel programmable ADSR.  The computer
has LOADS of digital latch outs and ins.  At least 64 bits.

I've also thought about providing an input to a summing network
for the PLL's VCO control voltage.  By supplying some CV that is
used to drive the master VCO, it might allow even faster step
changes.  This would be very nice for systems like mine that
multiply the frequency of the input.

>
>It was inspired by a graph of vibrato intensity vs. time for string players.
>Apparently, it is fairly typical to start with stronger vibrato on the
>initial step and then decrease the vibrato amplitude over the note. The
>Wogglebug is my attempt to build a circuit to do that function.
>
>Have you always wanted to be a member of a "Secret Society"?

(c:

>
>Now you can have a lifetime membership in "The Loyal Order of the Wogglebug"
>for only $20. You have to provide your own Fez but the Order badge can be
>viewed at
>
>http://groups.yahoo.com/group/wiardgroup/files/wogglebadge.gif
>
>and instructions for correct placement upon the Fez will be posted soon. Any
>color Fez is OK, but for safety reasons, we recommend it not be over 27"
>tall ;^)

LOL !!

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-- Scott Gravenhorst | LegoManiac / Lego Trains / RIS 1.5
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