Piezos have a high output impedance (capacitive, really), so you need an even higher input impedance on your mic pre or you'll get a "tinny" sound from the low end being rolled off.

A piezo with 1000 pF capacitance would have a reactance of 3 Mohm at 50 Hz, for instance, so if you wanted to pick up 50 Hz, you'd need an amp with several Mohm input impedance.

Signal Conditioning Piezoelectric Sensors from TI shows a circuit with 10 Mohm input impedance, for instance. Interfacing Piezo Film to Electronics suggests 22 Mohm and shows the most basic circuit you could use: one of these big resistors in parallel with a unity-gain buffer op-amp. If that level is too low, add two resistors and make it into a non-inverting voltage amplifier:

The major advantage of a charge amplifier, therefore, can be found when a long cable is used between a piezo film sensor and electronics. In addition, it also minimizes charge leakage through the stray capacitance around the sensor. Otherwise, simple voltage amplifiers are sufficient for most applications.

source

Piezos have a high output impedance (capacitive, really), so you need an even higher input impedance on your mic pre or you'll get a "tinny" sound from the low end being rolled off.

A piezo with 1000 pF capacitance would have a reactance of 3 MΩ at 50 Hz, for instance, so if you wanted to pick up 50 Hz, you'd need an amp with several MΩ input impedance.

Signal Conditioning Piezoelectric Sensors from TI shows a circuit with 10 MΩ input impedance, for instance. Interfacing Piezo Film to Electronics suggests 22 MΩ and shows the most basic circuit you could use: one of these big resistors in parallel with a unity-gain buffer op-amp. If that level is too low, add two resistors and make it into a non-inverting voltage amplifier (figure 9 b):

The major advantage of a charge amplifier, therefore, can be found when a long cable is used between a piezo film sensor and electronics. In addition, it also minimizes charge leakage through the stray capacitance around the sensor. Otherwise, simple voltage amplifiers are sufficient for most applications.

source

Piezos have a high output impedance (capacitive, really), so you need an even higher input impedance on your mic pre or you'll get a "tinny" sound from the low end being rolled off.

A piezo with 1000 pF capacitance would have a reactance of 3 Mohm at 50 Hz, for instance, so if you wanted to pick up 50 Hz, you'd need an amp with several Mohm input impedance.

Signal Conditioning Piezoelectric Sensors from TI shows a circuit with 10 Mohm input impedance, for instance. Interfacing Piezo Film to Electronics suggests 22 Mohm and shows the most basic circuit you could use: one of these big resistors in parallel with a unity-gain buffer op-amp.

source

Piezos have a high output impedance (capacitive, really), so you need an even higher input impedance on your mic pre or you'll get a "tinny" sound from the low end being rolled off.

A piezo with 1000 pF capacitance would have a reactance of 3 Mohm at 50 Hz, for instance, so if you wanted to pick up 50 Hz, you'd need an amp with several Mohm input impedance.

Signal Conditioning Piezoelectric Sensors from TI shows a circuit with 10 Mohm input impedance, for instance. Interfacing Piezo Film to Electronics suggests 22 Mohm and shows the most basic circuit you could use: one of these big resistors in parallel with a unity-gain buffer op-amp. If that level is too low, add two resistors and make it into a non-inverting voltage amplifier:

The major advantage of a charge amplifier, therefore, can be found when a long cable is used between a piezo film sensor and electronics. In addition, it also minimizes charge leakage through the stray capacitance around the sensor. Otherwise, simple voltage amplifiers are sufficient for most applications.

source