The circuit shown in this thread has inadequate input impedance (you want 10M for R1, not 1M), and the 5534 is absolutely not an option - use an FET-input op-amp such as the TL061 or TL071, or a more modern flavour of JFET-input op-amp. But it only ended on 2nd place when I put copper plate underneath the breadboard, without copper plate it ended up on 14th place (when powered from battery) and on 15th place when powered from power supply. Second place was BS170 mosfet, 10M:10M divider, 6k8 Rd, 4k7 Rs with Cs47u+510R. 047♟) since the bootstrapped grid circuit is very high Z. Picture 3 - Final version of the schematic. Thats basically it, but you need a wee bit more to bias the CF and block the dc voltages. As you can see, the switch in one position puts through the magnetic pickup, kills power to the preamp and disconnects its output, the other position does the opposite, obviously. But I agree that charge-mode is a very good idea - it has a very low input impedance, and that solves a lot of noise and interference problems. The lm386+piezo ended on 20th place so not very good. « Reply 11 on: October 30, 2011, 12:21:30 pm ». ![]() I've never used a charge-mode amp for a musical instrument piezo, simply because my guitars all came with factory piezos and onboard preamps. I used a charge amplifier configuration, the only way to keep noise pick-up low enough while getting the extended low-frequency response I needed. Click to expand.Years ago I was using a piezo sensor as an accelerometer sensing movement of a woofer cone. Re: Piezo / Mag preamp schematic, will this work « Reply 2 on: January 23, 2016, 11:16:53 AM » The input impedance of the MAG input is essentially R3 which is a bit low at 100K and will limit the high frequency response.
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