True bypass box with volume - problem

[Joeriz]

Hi there,

I recently purchased an envelope filter (3 Leaf Proton) which I really like.  Of course, EFs are finicky about the signal level that they are fed, generally preferring to be given more or less full volume from your guitar.  As such, I decided to build a true bypass box with a volume control built in and said volume control is only active when the loop is engaged.  That way, I can dime my guitar output and not have to worry about blowing people's ears out.

The box works perfectly EXCEPT when I engage the envelope filter. When it is engaged the volume control has almost no sweep and reaches max volume at less than 1/4 rotation.  When the EF is not engaged, the volume control works perfectly.  I am using a 100k audio taper pot.  I should also add that the volume control works fine when I substitute other pedals for the EF (e.g. an OD pedal).

Any idea what is causing this problem?  Do I need a higher value pot?  Something else perhaps?

Thanks,
Joe

[garcho]

What circuit are you using for gain?

[Joeriz]

There is no gain.  It's a simple passive bypass box with a volume control built in.

[GGBB]

The Proton is a Mu-Tron III clone, which I believe has a variable input impedance which goes from very high to very low as you increase the gain.  So if you are using a passive 100K volume pot in front of that which is already in parallel with the guitar's volume pot, and the Proton's gain is turned up so that it has a low input impedance, the pot will behave as you have described.  How does the volume work when you turn the Proton's gain all the way down?  But that's assuming the Proton has the same input section as a Mu-Tron III.  You should contact 3-Leaf and ask them.  Great pedal by the way.