Amplifier for an electret microphone

Discussion in 'The Projects Forum' started by arenwi, Dec 29, 2014.

  1. arenwi

    Thread Starter Member

    Dec 29, 2014
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    Hi to every body, I need to desing an amplifier to acondicionate mi signal from an electret microphone, always working with sinusoidal waves.

    I know inverters, rectifiers and more but I need another thing:

    I need an amplifier who generates an automatically offset. To fit all of the signal in the possitive part. I need to take the lowest value of the imput signal and put it to 0 volts.

    I attach you a picture.

    Any ideas??? Many thanks
     
  2. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hello, I´m trying to aconcionate an microphone electret signal to mi ADC to take Audio measurements.

    I need to use op amps in single suply.

    I was testing a lot of different circuits and I always have the same problem with the negative voltage

    This is mi last circuit:

    Captura de pantalla 2014-12-29 a la(s) 13.23.43.png

    I need to know the pick to pick value of the signal. If there is only positive signal I can doublethe this positive pick signal to ovtain the picj to pick.

    It could have problems becouse I didn´t know if the 0 volts of the output is the same 0 volts of the imput.
    The output signal could be a little moved up or down and we can´t see it becouse is no posible to see the negative part.

    Any Ideas?? many thanks

    Any idea??
     
  3. #12

    Expert

    Nov 30, 2010
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    Look at this:
     
  4. ericgibbs

    AAC Fanatic!

    Jan 29, 2010
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    hi,
    A Electret microphone requires a supply/load resistor, look at this image for an example.
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    It is part of almost every audio amplifier ever made. It is called a "coupling capacitor".
     
  6. Wendy

    Moderator

    Mar 24, 2008
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    You don't need a bunch of threads for what is basically the same problem, so I merged them.

    This might give you insight into the problem. Pay attention to the virtual ground.

    Project : Mono Preamp
     
  7. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hi to every body, I need to desing an amplifier to acondicionate mi signal from an electret microphone to an adc, always working with sinusoidal waves.

    I know inverters, rectifiers and more but I need another thing:

    I need an amplifier who generates an automatically offset. To fit all of the imput signal (sinusoidal + & -) in the possitive part for every different outputs.

    In other words, I need to take the lowest value of the input signal (negative value) and put it to 0 volts for every different inputs and ouputs.

    I attach you a picture.



    Captura de pantalla 2014-12-29 a la(s) 15.23.20.png


    Any ideas??? Many thanks

    Mod Edit: Again I have merged threads. Please don't open new threads and use the ones you have for the same subjects!
     
    Last edited by a moderator: Dec 29, 2014
  8. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Didn't I just answer this?
     
  9. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hi to every body and thanks for your fast answers.

    I was trying to write two different post at the same time, sorry I did.nt is no possible.

    I know the single supply collection pdf but I cant find on there mi solution.

    Bout the supply load resistor, Ericibbs told this. I like this, this night I will test it on board and tell someting about it.

    About Bill´s amplifier, I´m studing it.

    The coupling capacitors, I´m trying to use it but I think that if I have a problem of desing in my amplifier the condenser are not the solution, I was triying on mi circuit different values but is not the solution.

    I will inform about mi advances. Many thanks
     
  10. GopherT

    AAC Fanatic!

    Nov 23, 2012
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    image.jpg

    CORRECTION: The two 1k resistors should be 10k or so.
     
  11. ronv

    AAC Fanatic!

    Nov 12, 2008
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    Sometimes you need a lot of gain for the mic. In that case AC coupling the gain will eliminate the offset caused by the resistors.
     
  12. arenwi

    Thread Starter Member

    Dec 29, 2014
    37
    0
    Hi to every body and many thanks for your help.

    Yestreday I was asembling some circuits from this posts but with the same problems. The imput is a sine wave centred in volts.

    Circuits like posted by Ericgibbs, Gophert it give me also a bad offset, with good amplification but some noise inside this. (Many tahnks for it)
    This is what I have on the oscilloscope: (not a clean wave)

    IMG_4604.JPG

    I was also testing the Amplifier desing of of Bill_Marsen: http://forum.allaboutcircuits.com/threads/project-mono-preamp.91836/

    I is a very good amplifier, congratullations Bill, a good amplification with very low noise and very clean signal. This is what I had on the oscilloscope:
    IMG_4607.JPG
    In this case with the max gain the output was very good But I have a problem using smaller imputs:
    IMG_4609.JPG

    This amplifier always have a fixed offset of the middle od the Vcc. In this case with small signals we are loosing the a lot of BW mi ADC converter, look the red arrows, in this case are 1volt.

    Captura de pantalla 2014-12-30 a la(s) 11.27.48.png
    To use all of the BW of mi ADC I need an amplifier who can change its offset automatically. This offset must be the half value of the pick to pick voltage of the output. In this case the signal always came betwin 0 volts and it peak to peak value. This is what I need.

    Captura de pantalla 2014-12-30 a la(s) 11.40.39.png

    On this picture you can see that the output with differernt inputs Always came since 0 volts to each peak values.

    Any Ideas????
     
  13. arenwi

    Thread Starter Member

    Dec 29, 2014
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    0
  14. ronv

    AAC Fanatic!

    Nov 12, 2008
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    I think this may do what you want.
     
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