DOD 440 distortion

[lapsteelman]

Has anyone found a definitive fix for distortion in this circuit?

It functions fine and has great "quack", but their is a slight "fizz" on the notes. Especially when the sensitivity control is turned up.

I'm currently using the TL022 op amp specified...I've tried others,  little to no change.  I've added the resonance mod (220k resistor and a 250k pot in place of the 430k resistor). It works great, but the "fizz" remains......

I can't get the schematic from General Guitar Gadgets to load but that's the one that I used.

I've read that others have had this issue. Is it just the nature of the circuit?

[Mark Hammer]

Not sure what you're using for LDRs, but sometimes when sidechains react too fast, people perceive what they believe to be distortion.  It's not distortion, but envelope ripple that gives a kind of Scottish burr to the decay of notes.  I don't know that this is what you're hearing.  I just mention it as one of the options to consider.

[lapsteelman]

Thanks Mark. I'm using the specified VTL5C4 dual vactrol.

Hmm...I wonder if that's what I'm hearing?  It's a very "fizzy" kind of sound, It almost goes away if I adjust the sensitivity control so I just trigger the LED.

[Mark Hammer]

That would suggest a possible connection to the sidechain, because the level going to the filter is held constant.  The sensitivity control only adjusts what the vactrol is doing.

I made mine with a homebrew optoisolator, and don't get any ripple-related "frizz", but I have experienced it with other swept filters and things that used more responsive control elements.  F'rinstance, if the control element is a FET or bipolar transistor, one tends to get more of it.