by EWBrown » Sun Oct 16, 2011 3:48 pm
As I recall, piezo pickups require a fairly high first grid / loading resistance, on the order of 10 megohms, in order to not lose their full frequency response.
Usually the first high-mu amplidication stage will have a 10 megohm grid resistor, and the cathode is directly connected to the signal ground, with no cathode biasing, the grid gets its bias voltage a combination of "grid leak" and "contact" potential. Think very "old school" for this design.
I haven't experiment with piezos and their perticular requirements and issues, in a LONG time....
/ed B
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