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Piezo Preamp EQ

Discussion in 'General Electronics Discussion' started by Cris_PL, May 4, 2017.

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  1. Cris_PL

    Cris_PL

    3
    0
    May 4, 2017
    Hi!
    I made a circuit using this scheme: http://interface.khm.de/index.php/lab-log/piezo-disk-preamplifier/
    And it works great, I just have to just match the input resistor since the gain is too big.

    I need to add to this scheme a simple EQ correction, preferably low and high tones, possibly the same high tones
    I've arranged something like this based off a few other schemes:

    piezo + eq.png

    Is this correct? I have the impression that the correction system will interfere with the Gain potentiometer.

    I would be extremely grateful for the help, since it is already one of the last steps to finalizing the project.
     
  2. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    Your gain pot is messing up the tone controls, remove it.
    A piezo transducer makes a horrible microphone full of peaks at its resonant frequencies. Sometimes it is used in a drum or on the surface of a guitar.
     
  3. Cris_PL

    Cris_PL

    3
    0
    May 4, 2017
    Thanks for the reply! I need this gain pot, because this preamp is too sensitive. Maybe I can move it anywhere, for example to the end of this circuit? I use this preamp for metal drum, an instrument made from a gas tank).
     
  4. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    Put a gain pot on the first opamp instead, because a gain pot on the tone control circuit ruins it.
     

    Attached Files:

  5. AnalogKid

    AnalogKid

    2,414
    686
    Jun 10, 2015
    A better plan is to have IC1A be the variable gain stage only, and IC1B be the equalization only. In this way the tone controls will have constant source and destination impedances, which will lead to much more consistent effects.

    It usually is better to put the gain stage ahead of the equalization, so the bass and treble cuts reduce the gain stage noise.

    AG beat me by 5 seconds.

    ak
     
  6. Cris_PL

    Cris_PL

    3
    0
    May 4, 2017
    I made a prototype, it works very well, eq also works, only thing that does not work is gain control. Turning the knob just adds noise and I have the impression that it boosts the high end.
     
  7. Audioguru

    Audioguru

    2,999
    672
    Sep 24, 2016
    The high end is boosted if the value of the capacitor in the gain control circuit is too small.
    You must calculate the capacitor value for the cutoff frequency you want like this:
     

    Attached Files:

    darren adcock likes this.
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