*** Originally designed for PAiA FatMan
*** Must be adapted for other synthesizer systems
This circuit is a multi purpose phase locked loop designed for frequency multiplication (harmonic generation). 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 build this for a system other than the PAiA FatMan, you must design an appropriate attenuator or amplifier, whichever is necessary for your system or mixer. This should be fairly simple, being not much more than a voltage divider (attenuator) or an Op Amp buffer.
Much like a VCO (or in this case, 7 VCOs), 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. Wherever the source VCO's pitch goes, so does the phase locked loop. 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.
* DAMPING CAP
This switch cuts in or out an extra capacitor in the low pass loop 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 the 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. A sound that I can describe roughly as a 'dijery-doo' like sound is also possible. NOTE: in my unit this is a 10 turn pot. If a 10 turn pot is not available, I would suggest using a standard 5K pot in series with a standard 500 ohm pot. This will give you a coarse/fine control system that should work quite well. Use it by first centering the 500 ohm pot. Then set the coarse (5k) to get roughly the effect you want and fine tune it by tweaking the 500 ohm pot.
* MIXER POTS
7 pots are provided for mixing the harmonics generated by the
various counters. This is a simple, vanilla mixer.
Version 3.1 changes:
* LFO INPUT:
An input to the PLL for an LFO has been added. This input allows an LFO to modulate the frequency of the loop VCO. It allows a variety of effects depending on the frequency and amplitude of the LFO as well as the other PLL settings.
Here is a list of some harmonics and their interval relationship back to the fundamental:
2f 1 oct 3f 5th + 1 oct 4f 2 oct 5f maj 3rd + 2 oct 6f 5th + 2 oct 7f min 7th + 2 oct 8f 3 oct 9f 9th + 3 oct 19f minor 3rd + 3 oct 27f 6th + 4 oct