Better contact mics

As you may already know, my metal plate project will be utilizing a couple of contact mics for amplification and controlled feedback.
One of the downsides to the cheap piezo transducers is that, for electrical and mechanical reasons that I don't totally understand, a DIY contact mic without a preamp has a resonant peak in the response and can't reproduce low end well.
To that end, I am going into the workbench this afternoon to make a couple of preamps using this design:
http://www.zachpoff.com/diy-resources/alex-rice-piezo-preamplifier/