[sdiy] Benjolin filter issues

[David G Dixon]

I'm building a few Benjolin boards (based on the PCB layout and schematics
posted by Rob Hordyk on electro-music.com), and while testing them I noticed
that the filter was putting out a very weak signal (just a few hundred mV
peak-to-peak).  The oscillators are robust, and everything else is working
perfectly.  This problem is on both boards I've built so far.  I've even
simulated the filter part of the circuit, and the simulations give the same
thing.

I'm wondering, has anybody here built these things, and if so, did you
encounter similar problems?  Any help most appreciated!