Electret mic. & mixer with tone control

Discussion in 'General Electronics Chat' started by hazim, Jan 21, 2009.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    13
    In my electronics II project, I want to build an audio amplifier circuit with tone control and a two line mixer, one is a line in input (CD player, computer...) the other line of the mixer is fed by an electret microphone... Maybe my idea is not clarified (and sorry for my bad composition and English), but the pictures should clarify it....

    I hope you answer me quickly since it's late here and I will go buy the components tomorrow.

    First, how much output voltage does a powered electret mic. give directly (without a preamplifier)?? ranging in millivolts, I mean 1-100mV??

    Second, can I simply connect the electret mic. to one of the inputs of the sound mixer(see the attached circuits) or a have to build a preamplifier for the mic.??

    Finally, does it work if I connect the three-channel tone control to the output of the sound mixer/amplifier????
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,648
    2,346
    Hello,

    Most electret microphones need some power to function.
    Here is a page from the EDUCYPEDIA on microphones.
    http://www.educypedia.be/electronics/microphonestypes.htm
    Electret microphones are down the page.

    You also need a capacitor between the mic. and the potentiometer at the input of the mixer.

    Greetings,
    Bertus
     
  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
  4. bertus

    Administrator

    Apr 5, 2008
    15,648
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    Hello,

    Here is a PDF with some information on an electret condenser microphone.
    There is also a preamp shown in the PDF.

    Greetings,
    Bertus
     
  5. hazim

    Thread Starter Active Member

    Jan 3, 2008
    419
    13
    then the electret mic gives voltage in micro volts and the preamplifier amplifies the signal to milli volts???
     
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    5,005
    513
    I think your input potentiometers are far to high in value.

    They need to be an order of magnitude less than the input impedance of the transistor. Can you calculate this or do you need help here?

    For the line input the impedance should be 47k to 100K

    If your electret or condenser mike has an inbuilt FET then this figure is also OK for the mike input. Otherwise it needs to be several meg. That is why FETS are used.
     
  7. Audioguru

    New Member

    Dec 20, 2007
    9,411
    896
    Is it you or your teacher who found the mixer circuit from 1962?
    It has almost no gain because its input resistor values are much higher than the low input impedance of the transistor that has no negative feedback.
     
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