VC Butterworth Question

[Ian Fritz]

Filter Gurus --

Here's a little puzzle, if anyone is interested. I just built the VC
2-pole Butterworth on p. 5d(5) of the Electronotes Handbook. This is a
VC version of the standard C-2C design and was developed by S. Franco.
Bernie gave just a very rough schematic. I used CA3280's for the OTA's
and BB OPA132's for the buffers (to ensure low phase shift). I find it
has an unexpected pronounced peaking in the frequency response. It works
properly if I use equal-value caps rather than C and 2C. I can't believe
Franco made a mistake, so it must have to do with my implementation. 
Something about the current distribution at the CA3280 input? 

Does anyone have any experience with this or similar? I'm sure it
wouldn't be too hard to do an analysis, but I want to get along with the
building.

Thanks!

  Ian