Microphone Amplifier

Discussion in 'The Projects Forum' started by TBonius, Dec 19, 2013.

  1. TBonius

    Thread Starter New Member

    Dec 19, 2013
    4
    0
    Hi All,
    I've cruised the forum a few times but just joined because I have a problem that's whipping my butt. I have a Turner +2 desktop radio power microphone that I really like, so I thought I'd reproduce the circuit in a mobile mic. The circuit is based on a darlington 2N5306, of which I used an NTE172A(NTE equivalent). I copied the schematic I found online(which matches the mic circuit), and it works but the potentiometer doesn't adjust the output. I've been checking it with an amplifier and an oscilloscope, the Turner works as advertised but the circuit I built seems to be at full output regardless of the pot setting. I've tried another transistor, another pot, another element, the 5 electrolytic microfarad capacitor, but no joy. Any advice I would greatly appreciate.
     
    Last edited: Dec 19, 2013
  2. #12

    Expert

    Nov 30, 2010
    16,339
    6,824
    The 5k pot is not supposed to change the gain of the transistor. It just chooses where to tap into the output signal. The transistor is supposed to be at full gain all the time.

    Did I interpret your question correctly?
     
  3. TBonius

    Thread Starter New Member

    Dec 19, 2013
    4
    0
    #12, Thank you.
    After your observation, I looked at the schematic again from that perspective and it just jumped out at me that I had mistakenly wired the center position of the switch as the common. I'm sure I would have discovered this eventually, but after reading your reply, it was very obvious.
     
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