Piezoelectric Transducer Preamp


2010-12-30 7:09 am
Can somebody please clarify the woes regarding Piezoelectric transducers. I'm using such in my acoustic guitar. I'm confused in choosing the right preamp for it.

I know they have high impedance, they acts like a capacitor in circuit; and hence it needs a special preamp to get linear frequency response.

I've two preamp design, please give me some idea which to use, improvement options etc.

PreAmp#1: This is a simple differential amplifier design.

PreAmp#2: I've copied it from a Analog Devices Application Note.
I think this might be the best choice. But what is OP-41? I'll use NE5532 instead.

Suggestions/comments please...


2010-12-30 7:09 am
Here are the schematics


  • PreAmp#2.jpg
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  • PreAmp#1.png
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2008-07-08 3:24 pm
Your 2nd schematic is more likely to work than the 1st IMHO.However,as SY has already explained, NE5532 requires considerably high bias current, besides being a linear BJT IC, has only about 20,000k ohm input impedance.

What you really need is a charge amplifier when using a piezo disc & a high i/p impedance JFET IC for the buffer/input circuit
I've been experimenting extensively with piezo discs for the past 3 years & discovered many useful things!

TL072,LF353, OPA2134 or any very (high impedance) JFET opamp ONLY will work with piezo devices. But if you choose to use yours,then you may need to make the following changes to your circuit,as the opamp will otherwise be driven to saturation especially when driven by piezo discs!

1.C3= non polar .33uF to 1uF depending on your chosen -3dB cut off frequen
2.R1,R3 NOT required.

3.R3= make this 1M ohm - 4M7 ohm*

4.R5= 4Mohm-10M* ohm + a 4nF-15nF* high quality pulse/switching cap across across R5

*These values should be selected for desired gain/sensitivity.
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