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Old 30th December 2010, 08:32 AM   #1
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Default Piezoelectric Transducer Preamp

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...
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Old 30th December 2010, 11:23 AM   #2
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Here are the schematics
Attached Images
File Type: jpg PreAmp#2.jpg (75.1 KB, 217 views)
File Type: png PreAmp#1.png (5.4 KB, 204 views)
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Old 30th December 2010, 11:55 AM   #3
SY is offline SY  United States
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Quote:
Originally Posted by itheo92 View Post

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...
The 5532 will have a pretty high bias current for that application- you'd do better with a FET-input opamp.
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Old 30th December 2010, 02:08 PM   #4
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Quote:
Originally Posted by SY View Post
The 5532 will have a pretty high bias current for that application- you'd do better with a FET-input opamp.
Well, So it'd be better to use TL072, because it's a "LOW-NOISE JFET-INPUT OPERATIONAL AMPLIFIER". Right?

Do you think that PreAmp#2 will do the job better than the PreAmp#1 ?
Is there any other option?
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Old 18th January 2011, 10:19 PM   #5
teleman is offline teleman  Norway
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Hi,
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
cy.
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.

Last edited by teleman; 18th January 2011 at 10:24 PM.
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Old 18th January 2011, 10:58 PM   #6
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I agree with Teleman. A charge amplifier works very well with piezos.
here are 2 application notes that you might find useful:

http://goo.gl/GnPVj
http://goo.gl/uxrix

I have used TLE2072/TLE2074 JFET op-amps for piezo charge amps.

Cheers.

ZAP
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