Low gain on headset microphone

Discussion in 'General Electronics Chat' started by Mike mair 123, Sep 23, 2014.

  1. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    Hi,
    I am having a problem with an Avaya telephone and headset. I need to amplify the electret microphone with a preamp cct but can not use an external battery or power supply.
    Any ideas..
     
  2. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Electrets utilize a bias current usually supplied by the device the microphone is connected to. What is the mic connected to?
     
  3. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    Hi tanks for your reply.
    The microphone is connected to the telephone headset input which has an RJ 9 socket. The bias voltage I supplied from this port. if I amplify the mic with an pomp cct it works well but I need an external battery to power the circuit.
    Hope this helps
     
  4. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    Sorry that should have read op amp
     
  5. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    Is the electret mic ultimately connected to a standard phone line? If so, the phone line provides the operating bias. There is plenty of voltage/current available from a standard phone-line to run the electret and a follow-0n amplifier stage.
     
  6. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    The phone has a digital interface so it does not have power on it. I will test to see where the phone power is comming from and see if I can tap into it. I do know that some headset suppliers use an inline amp cable that derives the power from the microphone line. Prob with this is that the amplification is limited to what can be taken from the mic input. I would like to know how they do this as there are only 2 wires running to the mic. The audio is obviously superimposed on to the power lines and then decoupled inside the phone unit for further processing.
     
  7. alfacliff

    Well-Known Member

    Dec 13, 2013
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    our cisco irlp phones have a 48 volt supply hooked to them.
    was wthe mic working and then quit? or never working right?
     
  8. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    The phone is good but the headset port is very soft on the mic
     
  9. Mike mair 123

    Thread Starter New Member

    Sep 23, 2014
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    Never was ok
     
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