PLL (corrections added) text file
Scott Gravenhorst, Synthaholic
chordman at ix.netcom.com
Fri Sep 22 16:16:38 CEST 1995
PLL FREQUENCY MULTIPLIER MODULE Scott R. Gravenhorst
chordman at ix.netcom.com
This circuit is a multi purpose phase locked loop designed for
frequency multiplication. Although it was designed around a PAiA
FatMan, it should be adaptable to almost any analog system. The
circuit is based on a 4046 type micropower phase locked loop IC
and uses a divide by 12 counter inserted in the loop to force the
PLL's VCO to run at 12 times the input frequency. It's output is
provided as a set of 7 different square waves representing
octaves and perfect 5th harmonics of the input signal. If you
bulid this for a system other than the PAiA FatMan, you must
design an appropriate attenuator or amplifier, whichever is
necessary for your system.
This is a sound generating module, intended to enhance a synth by
tracking a VCO to produce it's own waveform at 7 different
harmonic frequencies. Because it is a phase locked loop, it has
characteristics of it's own, such as controllable lag and
over/undershoot when the input frequency changes.
The circuit works for a FatMan as designed and drawn. If you are
building this for a system other than a FatMan, you may need some
kind of conditioning for the 4046 input, such as a schmitt
trigger or op amp or both. This circuit works well with a -12V
pulse or square wave (pulsating DC, negative going) input.
This switch cuts in or out an extra capacitor in the low pass
filter circuit. It's use is not strictly defined and has
an effect on how quickly (or if) the loop settles down after a
pitch change. It has a dramatic effect on the playing range and
the sound produced.
This switch allows using either comparator built into the 4046
IC. Phase comparator 1 is a standard XOR type that has a
narrower lock range and will lock on harmonics of the input
frequency. Phase comparator 2 is a leading edge detector type
and has a much wider lock range and is resistant to locking onto
harmonics of the input signal. Wierd sounds happen when the
input frequency goes outside of the lock range of the loop.
Selects which VCO to which the loop locks.
PLO F MAX
Sets the maximum frequency the PLL's VCO can produce. To raise
the maximum frequency, turn this pot to a lower resistance value.
PLO F MIN
Sets the minimum frequency the PLL's VCO can produce. The MIN
and MAX pots will dramatically effect the operation of the loop.
The MAX control should be set to a lower resistance value than
the MIN pot to allow proper PLL operation. To lower the minimum
frequency, turn this pot to a higher resistance value.
This pot controls the damping factor of the PLL. It can be set
so that the tracking lag is short, long or even to allow
significant over/undershoot. Over/undershoot causes a 'sproing'
sound when the input pitch changes. This will be more pronounced
as the setting of this pot approaches zero ohms. When set to
higher resistance values, various damping effects occur. You can
get an interesting 'squink' sound at the attack of any note that
causes relatively large input pitch changes.
7 pots are provided for mixing the harmonics generated by the
various counters. This is a simple, vanilla mixer.
1F ..... Synth VCO frequency (remember the lag and overshoot)
1.5F ... Perfect 5th above synth VCO
2F ..... 1 octave above synth VCO
3F ..... Perfect 5th and one octave above synth VCO
4F ..... 2 octaves above synth VCO
6F ..... Perfect 5th and two octaves above synth VCO
12F .... Perfect 5th and three octaves above synth VCO
When I built this, I had some trouble with signal from the PLL
circuit 'bleeding' into the FatMan's output even with all of the
mixer pots to zero output. Oddly enough, the only way I was able
to get rid of it was to shield the power supply wires. I would
suggest keeping all wiring as short as possible.
I have had alot of fun designing and using this circuit. It
allows creation of yet more color and texture for electronic
sound and music synthesis.
I would like to thank John Simonton and Don Tillman for their
Please send comments by email to me (chordman at ix.netcom.com).
Every effort has been made to ensure that these documents, text
and GIF are free of errors. Please let me know of any problems
or areas where things are not clear.
-- Scott G., Synthaholic
There is no 12 step program for synthaholics. Thank your Superior Being.
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