AUDIO AMP. PROBLEM.-IDENTIFYING THE MIC. TYPE.

Discussion in 'General Electronics Chat' started by firebreather, Nov 23, 2014.

  1. firebreather

    Thread Starter New Member

    May 27, 2013
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    I am trying to make an audio amplifier using one op-amp and 5 V supply. The problem lies with the identification of the microphone,whether it is an electret,condenser or some other type. I bought it from a general audio spares shop for a cheap rate, small enough (size of a fingertip) to fit on a breadboard. I searched a lot on the internet to identify a similar looking device, all they have is the pictures of electret microphones. Now I am confused as the type of microphone is very essential to start my design,because some have a FET preamplifier inside, some need a bias voltage,etc. It is cylindrical with black plastic sides and metal exposed on top and bottom. There are 5 small holes on the top at the centre. At the bottom two pins come out. The juncture of one of the pinsis encircled with black paint .

    Please can anyone look at the picture and tell me the type and its specifications ?
     
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  2. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    Simply first assume that you have a electret microphone with a built-in JFET and do the practical test on the breadboard.
     
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  3. firebreather

    Thread Starter New Member

    May 27, 2013
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    But if so , what value of resistance should i connect from the supply to the mic. for the built-in pre-amp, so as not to damage it ?
     
  4. Jony130

    AAC Fanatic!

    Feb 17, 2009
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    So you didn't watch the video? Use 4.7K for example.
     
  5. ian field

    Distinguished Member

    Oct 27, 2012
    4,415
    783
    Most electret mics require a supply, either a battery compartment in the case or a stereo type jack so +5V can be supplied to it via its lead - the uncased bare component mic is a small capsule, usually about 10mm diameter (much smaller in mobile phones).

    A crystal mic has massive resistance, probably too high to measure, they usually exhibit some capacitance.

    A dynamic mic has probably no more than couple of hundred Ohms - likely far less, it will be inductive.

    A carbon mic will probably be heavier and bulkier - probably also near 200 R, hook it up to a resistance meter and blow into the sound hole - you should be able to lower the resistance reading.

    For a low impedance mic - consider a common base transistor input stage, its a better impedance match and plenty of voltage gain.
     
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