Paul in the lab's CMOS Theremin faint sound

[zombiesonore]

Hello everyone,
I've design a single sided PCB and build this CMOS pseudo-theremin:
https://paulinthelab.blogspot.fr/2012/04/theremin-veroboard.html
It seems to work a attended except that the output is very faint.
If I set my guitar amp at a level that would be OK for my guitar, the cmos theremin is barely audible.
My questions: does someone here have built this project? Is it the normal behavior?
Thanks in advance!
Etienne

[zombiesonore]

You-ou? Nobody ever built this one?