PLL (corrections added) text file

Scott Gravenhorst, Synthaholic chordman at
Fri Sep 22 16:16:38 CEST 1995

PLL FREQUENCY MULTIPLIER MODULE            Scott R. Gravenhorst
                                         chordman at

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.

VCO 1/2
Selects which VCO to which the loop locks.



Sets the maximum frequency the PLL's VCO can produce.  To raise 
the maximum frequency, turn this pot to a lower resistance value.  

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  

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

-- Scott G., Synthaholic

There is no 12 step program for synthaholics.  Thank your Superior Being.

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