Leafcutter John has a great post about making Rochelle Salt, which is piezoelectric, and hence can be used as a contact mic: [http://leafcutterjohn.com/?p=1518 Real Sound Cookery].
My folks [http://blogs.ch.cam.ac.uk/pmr/ Peter] and Judith are both crystallographers, so I thought I'd put them to work in the lab (kitchen) to make some nice crystals.
We followed a pretty similar procedure to Leafcutter John, along with some extra info from the crystal guide [http://www.homepages.ucl.ac.uk/~ucfbanf/general/crystal.htm here]
[http://mattvenn.net Matt] put this picture of the next round of Piezo Preamp boards up on his [http://www.flickr.com/photos/matthewvenn/7142271029/in/photostream/ Flickr Stream]. I've removed the piezo -ve input, and tied it to ground, which might loose 3dB of gain, but makes figuring out ground planes a lot easier. I couldn't hear the difference when I shorted piezo -ve to ground, and it makes the layout much smaller and easier. We're down to about 50% of the original size now.
Got the first set of boards from [http://mattvenn.net Matt Venn] for prototyping piezo preamps, and they're great! I've soldered both boards, after using the JFET matching described [http://www.nrgrecording.de/html/fetmachting.html here] (NOTE: link seems to be dead - I'll copy the circuit diagram from my notebook).