Switch Phase Locked Loop IC on/off based on input signal

[spacekid71]

Hi everyone,

I was wondering if there is a way to switch on and off a Phase Locked Loop IC like the LM565CN based on the input signal to a guitar pedal being present/absent. The LM565CN datasheet can be found at: https://www.findic.us/doc_download/52704468

I noticed that it kills the sound when I connect pin 7 (VCO Control Voltage) or pin 8 (timing resistor) to ground, but I am not sure if this would be the right way to do this. Also, I would need have some type of switch based on the input signal...

It would be great if someone could point me in the right direction.

Thank you!

Martijn

[anotherjim]

Depends on what you're trying to achieve. A problem with PLL pitch followers (if that's what you want) is the glitching that can occur when your input comes and goes. I think it's better to control the audio output in response to the input signal so that the PLL glitching has less chance of being audible.

The 565 (which is obsolete) has no enable input. The currently available CD4046 does have a VCO enable pin.
Grounding the control resistor might place a short circuit on the pin.
Grounding the CV input would, in a pitch follower, discharge the loop filter capacitor and delay the time it may take to pick up the input pitch on a new note.

If you leave it running and mute the output elsewhere, the VCO moves to the "centre" frequency set by the timing R & C values which on average may let it get to the next pitch quicker. The CD4046 being high impedance CMOS, can have the loop timing capacitor used as a sample & hold for control voltage with a CMOS switch like the CD4066 so it can stay on the last pitch and in a melody have more chance of getting to the next note played.

[ElectricDruid]

+1 agree with Jim.

The way I would approach this would be to mute the output rather than try and turn the VCO on and off. You'd need an envelope follower design to extract the input signal's level, and then a OTA/VCA to control the VCO's output. The hope would be that by the time the input signal is at such a low level that the PLL can't follow it, the output is muted enough that you can't hear it either.

You *could* gate the VCO, but it's likely to add more glitchiness to something that's likely to be pretty glitchy anyway (PLL pitch tracking isn't that fantastic, and certainly don't expect polyphonic results!)

[StephenGiles]

https://www.dropbox.com/sh/y9xpi9rb2z291ij/AAB5q_ps58mn_lAKm_p4Uoxda?dl=0

This may be of some help. I got this circuit back in the days when we used to send a letter request!!!

[amptramp]

Keep in mind the second harmonic in a guitar can be higher level than the fundamental so a PLL connected to the output can go into a "wolf note" like a viola - a sudden change to double the frequency or an octave up.  If you want to drive a PLL with a guitar, use the neck pickup only (which has the strongest fundamental) and use a lowpass filter to reduce unwanted harmonics.  There may be ways to control the filter rolloff on the fly from the guitar signal but tracking filters have some of the same problems as PLL's - how to keep them from syncing to the wrong harmonic.