Make a PLL Hold a Frequency?

[thehallofshields]

Hey guys, I'm playing around with the 4046 and I'm really curious how a circuit like the Boss DF-2 can lock a frequency and sustain it after the input is removed.

Please tell me it's not something super complex like Frequency-to-Voltage > Momentary Switch controlled Sample & Hold > Tuned VCO

[PRR]

http://rudn2.nodevice.com/preview/big/322/322272-2.jpg
http://www.diystompboxes.com/smfforum/index.php?topic=113801.0

I did not study it; but looks like the '4046 phase comparator goes to a simple sample/hold to the VCO In.

The Fundamental Detector is more complicated.

[thehallofshields]

I'd love to 'Chop' the DF-2; get rid of the complicated switching, distortion section, LFO, maybe even the envelope generator, but that's well beyond my ability.

Where do you see the Sample & Hold? I suspected that's how it was sustaining a note, but the switching and 'main board' area is so complicated I can't find it.

[anotherjim]

It's the CMOS switch 8a. When "open" the VCO control volts to pin 9 of the 4046 is left as it was, so long as the loop filter capacitor C37 can hold it.

[thehallofshields]

I see. It makes sense how the Vibrato is achieved with just the LFO and not a Delay chip or the usual methods.
The LFO is just giving a trickle of current through the 1M resistor, which slightly offsets the S&H voltage held by C37. 

[thehallofshields]

So, correct me if I'm wrong, but if I put a momentary switch between pin-13 and pin-9, and a small-ish RC>Gnd on pin-9, I should be able to 'lock' a frequency on other PLL circuits as well?