Tom G's vcf2e - questions on modifications

[Sean Costello]

Hi all:

I recently received a few of Tom G's vcf2e boards in the mail, and they look
very nice. My eventual goal is to convert a few of the boards into stand-alone
Moogerfooger-type boxes, to play my guitar through. I plan on having the vcf2e
board, and an additional small board for modifications, installed in a large Bud
project box (the size would be the one used for several commercial Univibe
clones), with plenty o' fooswitches for true bypass, envelope follower on-off,
LFO on-off, audio-FM on-off, etc. I have a "dream box" in mind, which shouldn't
be too difficult, but I would appreciate y'all's input; for reference, the
schematic is online at 

http://www.mindspring.com/~vco/vcf2e/vcf2e.html

A few of the mods I would like to do are:

- Audio rate FM, where the input is FMing the filter cutoff. I think that
tapping the signal from the input of the envelope follower (i.e. after the 1st
opamp stage, where the signal is amplified before going to the full-wave
rectifier), and sending this signal through a volume control to the summing
point of R11, R12, and R13, should do the trick. Does that sound right?

- Converting the envelope follower into one with seperate attack and decay
times, and the ability to extract a gate/trigger signal. I think that I should
be able to do this with an additional dual op-amp, following the full-wave
rectifier stage of the envelope follower. One stage of the op amp would
basically be an AR-envelope generator (with the op-amp acting as a buffer), and
the second stage would be a comparator to extract a gate signal (I think - I am
going from memory here); an additional third stage could be set up as a
differentiator to extract a trigger. Electronotes had a similar circuit, using
an LM3900. Any ideas? It would be nice to have a circuit where the gate/trigger
threshold could be set at such a level that quieter notes can be followed by the
envelope follower, while very loud notes trigger the AD-envelope generator.

- Putting an effects loop in between the envelope follower input and the input
to the filter. I was originally going to just build a simple clipping circuit
into the design, but I realized I may want to have a combination of effects,
such as distortion followed by chorus, with the envelope follower using the
clean input as the signal to be followed. Do I need to use buffers for this, or
can I just cut some traces and use some switching-type jacks here?

- Finally, do I need to use any input-output buffers or preamps for guitar? Any
recommended types? Op-amp, FET? What sort of input stage would allow me to have
filter overdrive as an option, with a guitar-level signal?

I would appreciate any and all input that people might have, as well as any
additional ideas for modifications. I am excited to build up my dream filtering
pedal!

Sean Costello