The PZP-1 is available for purchase.
Piezoelectric pickups are popular in acoustic or semi-acoustic instruments such as the Fender Acoustic/Electric Fretless Precision bass. A properly installed piezo pickup, coupled with correct electronics, can accurately reproduce vibrations from the subsonic to the ultrasonic frequency range. Unfortunately, piezo pickups have a reputation for being “quacky”, trebly, and lacking depth. This is usually because of poor electronics.
To work properly, a piezo pickup must be connected to a 5M to 10M ohm input. Ordinary guitar amp inputs, with impedances on the order of 100k to 1M ohms, are too low; mixer line inputs, with impedances on the order of 1k to 10k ohms, are absurdly too low. Combined with the internal capacitance of the pickup, these low impedances create a high-pass filter that robs the pickup of its bass response and exaggerates the treble. Attempting to blend a piezo pickup directly with an electromechanical pickup (impedance on the order of 10k ohms) will not work well.
The PZP-1 was designed as a retrofit for the Fender A/E bass, which (at least in early versions) had inadequate buffering of its piezo pickup. The PZP-1 is inserted between the pickup and the rest of the active electronics. Its input impedance is 10M, which allows the piezo to develop its full bass response. Its output impedance is adjustable in the range of 10k, in order to easily blend with the electromagnetic pickup.
Although the PZP-1 is primarily aimed at instruments that combine piezo and electromagnetic pickups without proper electronics, many luthiers have found it convenient for use even in purpose-built new instruments. It has been used for violin, erhu, bass, guitar, cajon, hurdy-gurdy, and myriad other instruments.
Until I manage to recreate my online store (taken down by Russian hackers a couple years ago), if you wish to purchase a PZP-1 you can contact Cafe Walter Audio on Facebook, let me know what you need, and I’ll send you a PayPal invoice.