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Two stage class A amplifier

Discussion in 'General Electronics Discussion' started by FlyingMan, Nov 14, 2016.

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  1. FlyingMan

    FlyingMan

    3
    0
    Nov 14, 2016
    Hello.
    I simulated a two stage amplifier and I have a question regarding it. In simulation when the signal is applied the output of q2 shoots out to Vcc 12V then it stabilizes around operating point, why does it happen?

    Vcc 12 V
    Freq 27 kHz
    input signal sine wave 50mA peak to peak.

    Blue line is Q1 colector output
    green is Q2
     

    Attached Files:

    • Sim.jpg
      Sim.jpg
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  2. Audioguru

    Audioguru

    3,040
    678
    Sep 24, 2016
    Why is the value of C4 500 times the values of C2 and C3?
    Why are all the resistor values so low causing their currents and the transistor currents (and heating) to be so high?
     
  3. FlyingMan

    FlyingMan

    3
    0
    Nov 14, 2016
    This is my first amplifier design, I simulated it to try to understand how it works. Random C values are there because i tried to mess with them to check if they are cousing q2 12V jump. Values for resistors are low because i will not build this version of amplifier so energy losses are not my concern at this stage.
     
  4. Audioguru

    Audioguru

    3,040
    678
    Sep 24, 2016
    I tried simulating your circuit and it worked perfectly but I cannot read your "tran" on your post. You have a start delay of 0.1m that I have never used.

    The simulation is not real because its capacitors are already charged when the sim begins.
     
  5. FlyingMan

    FlyingMan

    3
    0
    Nov 14, 2016
    tran is 0.5m = sim time 500us. I did put delay there to make q2 jump more visible. So there is no q2 jump on your sim?
     
  6. Audioguru

    Audioguru

    3,040
    678
    Sep 24, 2016
    Your emitter resistor bypass capacitors C2 and C3 have their value too small so they are attenuating the 27kHz signal but are passing the fast acting higher frequency pop at full amplification.
    I increased their value from 0.1uF to 1uF and now the pop has less level than the signal.
    Your C3 is my C4:
     

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