Microphone Sensitivity

Discussion in 'The Projects Forum' started by JDR04, May 2, 2012.

  1. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Could somebody please help me out with this.

    The attachment shows a preamp I have built and is working:)

    Now I'm wondering how does one incorporate a microphone sensitvity adjustment to this circuit. Any ideas will be appreciated.

    Also, what software do you guys use to post schematics? My hand drawn ones are getting embarrassing.

    Thanks a lot - JDR04
     
  2. #12

    Expert

    Nov 30, 2010
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    6,744
    I make the 200k into a pot.
    I use MSPaint to make drawings.
    Other people use simulators and post drawings from those.
     
  3. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Thanks for that.

    Just so I understand this as I am new to electronics. The 200k pot will adjust the level of amplification instead of adjusting the level of signal from the microphone itself??
     
  4. wayneh

    Expert

    Sep 9, 2010
    12,087
    3,026
    Yes, the amplifier gain. You'd only look to attenuate the amp input if it was exceeding the range of the amp, and that's not likely with a microphone against the 9V supply.
     
    Last edited: May 2, 2012
  5. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Thanks Wayneh, lastly, what do I look for in the amps datasheet to establish what is the maximum gain value for this IC. Is there a special name for it other than gain?
     
  6. #12

    Expert

    Nov 30, 2010
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    Large signal voltage gain.

    Fig.8 large signal frequency response.
    Fig. 5 open loop frequency response.
     
  7. JDR04

    Thread Starter Active Member

    May 5, 2011
    339
    4
    Many thanks to #12 and Wayneh for your time and knoweledge. It is appreciated-JDR04
     
  8. #12

    Expert

    Nov 30, 2010
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    Besides, the less <snip> you hang on the input side, the less background noise you will generate. Not a problem with a mic that has an internal pre-amp, but a good habit to get into.
     
  9. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    The lousy old LM324 quad opamp (4 opamps, 14 pins) is too noisy (hiss) to be a mic preamp, has horrible crossover distortion and has a full output bandwidth to only about 2kHz. With a voltage gain set to 200 then it cuts frequencies higher than only 2kHz.

    Your circuit has the (+) reference voltage at 0V instead of at half the supply voltage so the opamp will be a rectifier and produce extreme distortion.

    My mic preamp uses an inexpensive TL071 low noise very low distortion audio single opamp in an 8-pins package that works well up to 100kHz.
     
  10. #12

    Expert

    Nov 30, 2010
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    This being a powered microphone, wouldn't that suggest it has a pre-amp inside it?

    Still, that circuit by AG covers all the bases and saves a lot of back and forth about how to make a bias circuit.
     
  11. atferrari

    AAC Fanatic!

    Jan 6, 2004
    2,644
    759
    Look for the hand drawn Bob Pease's schematics.

    Yours are much nicer.

    Do not worry.

    Ah... then read about who he was.
     
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