How to connect piezo to amplifier module

Discussion in 'General Electronics Chat' started by oknimie, Mar 12, 2018.

  1. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hello, I am trying to connect piezo(s) to amplifier module, such as adafruit MAX98306 and speaker. However it is not working. When I connected piezo to sound mixer or zoom H4n, it picked up the sound. I was wondering if anyone had any suggestions on the best type of amplifier module to use, preferably small ones.

    Thank you in advance!
     
  2. Tonyr1084

    Well-Known Member

    Sep 24, 2015
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    Are you using it as a microphone or as a speaker?
     
  3. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hello! I am using it as a contact microphone.
     
  4. RichardO

    Senior Member

    May 4, 2013
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    Which Piezo transducer are you using?

    Normally they only have a few hundred picofarad of capacitance. This capacitance is a very high impedance at audio frequencies. This means that you need an amplifier with a really high input impedance to get the low frequencies.
     
  5. sghioto

    Active Member

    Dec 31, 2017
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    The MAX98306 is designed for line level input. You will need a preamp.
    SG
    https://www.sparkfun.com/products/9816
     
    Last edited: Mar 12, 2018
  6. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi RichardO,
    I am using the 20mm diameter piezo (the common one. But I am thinking of using 5mm diameter also.
     
  7. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi sghioto,

    Thank you. I will get the preamp. Would I combine MAX98306 and the preamp or use the preamp alone?
     
  8. sghioto

    Active Member

    Dec 31, 2017
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    Connect the output of the preamp to the input of the MAX98306 if that is the audio chip you want to use. The MAX98306 is a dual amp designed for stereo output.
    SG
     
  9. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi sghioto,
    Thank you, I will try it out!
     
  10. RichardO

    Senior Member

    May 4, 2013
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    Please post the specifications for your Piezo's. I think you will find that they only have about 1000pF of capacitance. to get a 20 Hz lower frequency cuttoff you will need about 10 Meg ohms input impedance on the amplifier.

    This amplifier only has about 15 K ohms of input impedance. :(

    You need either use an op-amp with a FET input or make a buffer amp using a J-FET. If you make a buffer amp you can use the circuit like used in an electret microphone.


    Speaking of electret microphones... A real microphone will have much better frequency response than a Piezo element. Look at the frequency response of your Piezo transducer to see what I mean. Note that it has a very sharp peak in the frequency response and lots of other peaks, as well.
     
  11. ian field

    AAC Fanatic!

    Oct 27, 2012
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    It will work with the special JFET in an electret mic capsule. You might not even need any more amplification than that, but its not difficult if you do.

    Common or garden JFETs like the 3819 sort of work, but salvaged from a capsule is better.
     
  12. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Thank you for your suggestions!
     
  13. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi Ian,
    Thank you, I will look into JFET. When you say special JFET in an electret mic capsule, do you mean JFET in a piezo contact mic capsule or I take out an existing JFET in electret mic capsule and connect it to piezo?
     
  14. RichardO

    Senior Member

    May 4, 2013
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  15. ian field

    AAC Fanatic!

    Oct 27, 2012
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    The JFET in a mic capsule, I made contact mics/vibration sensors with various piezo elements. The JFET settles close enough to bias a TL431, a resistor provides DC nfb to stabilise the operating point, but you have to split the resistor and add a capacitor to shunt AC nfb - so much gain it could demonstrate that some non polarised capacitors are microphonic. The long thin piezo from a lighter produces huge output.
     
  16. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi Ian,

    Thank you very much, I will try it out!
     
  17. oknimie

    Thread Starter New Member

    Mar 12, 2018
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    Hi Richard,

    I see, thank you.
     
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