MOTM

Does anyone have any suggestions how I could add an envelope follower
to my MOTM format modular??  I'm looking for something that already
has a panel available.  I know I can get envelopes out of an 820
(although it doesn't have a rectifier), and I added an envelope out
to my modded Blacet Time Machine (it also has an "Alias" Knob), but I
could use at least one more way to extract an envelope from an
external signal.  It doesn't have to extract a gate, include a
pre-amp, or separate controls for up and down.  Just a simple circuit
with a rectifier followed by an adjustable low-pass filter would be fine.

Any ideas??

Thanks :)