After two and a half years and thousands of Phantom Piezo Preamps sold, we finally ran out of 2SK596S-C JFETs (which have been discontinued for some time by On-Semi). Going forward, the best option is the Fairchild PF5102 (now also an On-Semi product). We have slightly redesigned the Phantom Piezo Preamp PCB to allow for the use of the ‘5102 (which has a different pinout to the ‘596) and also we have incorporated a pair of zener diodes across the input to protect the circuit (and your loudspeakers) from large voltage spikes (which will be generated by a piezo transducer if you give it a significant physical shock). As a result, the redesigned PCB is 1mm longer than the old one.
Apart from the above, the design is unchanged. We have built prototypes and performance is excellent. The new preamps are available in the shop here and a version with the XLR not soldered is also available for those who want to hard-wire the output.