DECAY/ TRAIL OFF CIRCUITS?? (track and hold?)

[loss1234]

can anyone point me toward a schematic that has a pretty clear example of how to set up a circuit to HOLD the end of a note? this would be used in guitar synths or in octave pedals, anything where the end of the note starts sputtering away or turning to noise.

i see a few that use 4046's and 4016's and i was hoping to find a way to do this (sample a voltage and store it in a cap) without a 4046. I had heard that the MXR bluebox does it but i cant find any 4016 or switch in the schematic...how does it hold the end of the note?

this is one of those areas of circuit building that i have been trying to get working for days and days and if only i can figure out this block then i can build what i want

ANY Help, guidance, or links appreciated.

[Processaurus]

Boss kinda does that in the super distortion/feedbacker DF-1.   Why no 4046?  Might as well use what is available to you, and they're cheap.

[loss1234]

i guess if i could get the 4046 to work! the boss schematic you refer to just looks really complicated!
i dont need so much of the circuit so i was HOPING there was something out there that might demonstrate the concept.

but i guess i will have to try to build that thing.

if i was JUST going to focus on the hold/vco part of it, what could I use to turn the 4016 on and off instead of a pedal (in other words, would the signal itself (acting like a gate) be enough to tell the 4016 when to store the voltage and when not to?

[loss1234]

Ok
i built the 4046/cap section of the FD2 (minus all the other stuff) now it holds when i plug the 4016 low (by plugging a lead into gnd) but IS there a way to get this to go low when the note begins to die out? (i know there is such a circuit embedded in a few guitar synths but i have never been able to figure out which section or just how it works.

my guess is that maybe a gate (which is set to die at a threshold point) could be used but i dont know quite how to get audio turned into a gate. i will take a look around for an old Preamp module schematic i have which has envelope follower and gate and trigger. its not a small circuit though so if anyone knows of an easy way to get a +5v gate out of a guitar signal, let me know

thanks

[Mark Hammer]

As I understand it, "holding" involves hanging on to a voltage that represents the note played (or to be generated).  Maintaining the voltage for any appreciable time involves having a) a capacitor that does not spontaneously leak stored charge very easily, and b) high-impedance isolation of the charge stored in the cap such that it does not leak out by other paths very quickly.  This latter aspect is why you will always see the op-amps associated with S&H to be Bi-Fet op-amps.

[loss1234]

mark

yeah i got that part working. i am using a low leakage cap and it works great BUT i now need something OTHER than a foot pedal (like in the original schematic) to trigger the hold. i would like it to be automatic, as opposed to stepping on a pedal when i want it to start holding. there is a MINI SYNTH on GGG that has a feature like this and it sort of works but not too well.

so i think i am going to try building this :

http://www.musicfromouterspace.com/analogsynth/SOUNDLABMINISYNTH/guitar_trigger.html

and use the gate from this to tell the 4016 when to initiate the hold.


but even from doing it with a switch its a very cool effect being able to sustain the note for awhile.!

thanks

[puretube]

(Mostly addressed to Mark & Processaurus, cc. the B*ss approach:)
just having thought the Envelope Follower thought in the other thread:
how about heterodyning the guitar-signal into (lower) RF-territory,
having the PLL locking into the new high frequency much quicker than usually in the AF-range,
and then heterodyning the locked frequency back down again???   ()

[frequencycentral]

I just added a useful schematic to your other thread.