Issues with MXR envelope filter build.

[Galego]

I've built an MXR Envelope Filter and although it works, it has a weird theremin like effect that changes how the effect behaves depending on how close you are to it.

Does anyone have an idea what could be causing this and how to solve it?

[Galego]

Anyone? 

[Govmnt_Lacky]

  Bad grounding causing an antenna 

[Galego]

Bad grounding causing an antenna 

How? Cold solder point?

[Govmnt_Lacky]

How? Cold solder point?

You could have a ground loop that is causing an antenna somehow.... I am just spitballing here.

Pictures, layout, voltages would not hurt...  More pictures and layout info since the circuit apparently "works" according to your OP.

I read on Tonepad that certain CD40XX chips did not function well in the circuit as well.

[Mark Hammer]

The EF contains a high-frequency clock whose pulse-width is varied by the envelope.  My gut tells me there is a wire/layout issue which is permitting that HF clock to be influenced by something.

[Galego]

How? Cold solder point?

You could have a ground loop that is causing an antenna somehow.... I am just spitballing here.

Pictures, layout, voltages would not hurt...  More pictures and layout info since the circuit apparently "works" according to your OP.

I read on Tonepad that certain CD40XX chips did not function well in the circuit as well.

Video: http://www.youtube.com/watch?v=3JcZrlt3xC0

Layout:

Picture (still missing the middle switch for reverse sweep):

The schematic i used was the one from GGG. Added a mod to change the value of R17, to control the Decay.

I had noticed this problem when i was testing it, and it seemed to be restricted to touching the threshold pot. But still, it sounded just fine here. But the guy who i built it for, seems to have more trouble getting it to work properly, and i'm a bit lost on what to do to fix it...

[Galego]