Wah pedal blues

[duffrey]

I have recently completed a vox wah pedal build, and everything seems to work perfect except for the sweep cap that I rigged up.  
Instead of using a whole bunch of fixed value caps, I decided to implement the old variable input cap trick.  So I have a very small value cap on one side, then a 100K pot, and a large value cap of the other side, to blend them together to get a wide variety of sweep ranges.  
But, sadly, it does not work so good.  When I use it the sweep remains really high, until I turn the pot all the way to the other cap, then all of a sudden it gets really low.  (perfect in fact for playing bass)  So there is no inbetween.  
Should this work in this particular circuit?  And if so, any suggestions?  
Thanks guys.

Jeff