Barry & Chris --

Piezo devices are often used with charge amplifiers, which is just an
op-amp with capacitive feedback and a parallel resistor to keep it from
drifting off scale.  When the input is connected to the Piezo device (a
capacitor) the op-amp circuit acts as an amplifier with gain of CZ/C1.  The
low-frequency limit is given by the time constant of the resistor and C1.
Op-amps with very low input bias and offset currents must be used.  This
circuit provides a low-impedance output to drive other circuitry cabling,
etc.  With some of today's op-amps having input currents in the picoamp
range, this type of thing is quite viable.

Use teflon standoffs for the connections at the inverting input of the
op-amp.  And any cabling used between the piezo device and the circuit
should be made with wire having insulation with very low dielectric
absorption.

Karl


          +--------------\/\/\/\------------+
          |                                 |
          +----------------||---------------+
          |                 C1              |
          |             |\                  |
          |             |  \                |
          |             |    \              |
          |             |      \            |
          +-------------| -      \          |
          |             |          \        |
          |             |           \       |
   Piezo ---            |            >------+------------O
     CZ  ---            |          /
          |             |        /     
          |       +-----| +    /
          |       |     |    /
          |       |     |  /
         ---     ---    |/
         \ /     \ /
          V       V


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