Having problem with an emitter follower

Discussion in 'The Projects Forum' started by yoan03, Dec 6, 2013.

  1. yoan03

    Thread Starter New Member

    Dec 5, 2013
    4
    0
    Im trying to built an amplifier to listen a mic's signal on a speaker. I tried the circuit in a breadboard only with a common emitter amplifier but the amplifier's gain was lost due to the speaker resistance. So, I found out in "electronic devices" by floyd that I need an emitter follower to accomplish this.

    I rebuilt the circuit again, and I could listen the mic in the speaker but when the mic is not getting a voice signal, there is a 60hz or so oscillation noise in the speaker, and I plug the oscilloscope and I see that the emitter follower is working as a class-B amp just working in the positive part of the signal, and ignoring the negative. I tried it in multisim and the same results , but the only difference is when I disconnect the function generator (Mic) and dont get the 60hz noise just a constant voltage.

    I uploaded the circuit and the voltage reading from both amplifier using multisim the one in red is the common emitter and the other the emitter follower.

    My question is what can be done to make the emitter follower work as a class-A amplifier?

    Sorry for my bad english :)
     
  2. BobTPH

    Active Member

    Jun 5, 2013
    785
    114
    That is becuase it can only sink current through a 165R resistor.

    A much lower resistor would make it better, say 15R to stay within the current limit for a 2N2222.

    Also, to get a lot more gain:

    change RC to 10K Ohms
    R1 to 220K
    R3 to 33K


    Bob
     
    Last edited: Dec 6, 2013
    yoan03 likes this.
  3. yoan03

    Thread Starter New Member

    Dec 5, 2013
    4
    0
    Thank you man, I tried it and it worked like a charm! :)
     
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