Attentuation, Shifting and Distortion in the output of amplifier

Discussion in 'General Electronics Chat' started by PersianEngineer, Oct 20, 2013.

  1. PersianEngineer

    Thread Starter New Member

    Aug 15, 2013
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    0
    I'm simulating an audio amplifier with uA741 in pspice (student version).
    the input signal is 0.1v or 100mv sine wave with frequency 1kHz and 10kHz. the theoretical gain is 33 but in simulation, the gain of output is only 3 and we have shifting and distortion.
    as we know, the slew rate is 0.5v/microsec and if we calculate the max slew rate needed for my input signal using below folrmula, we get a value much smaller than slew rate of uA741.

    slew rate = 2 PI x f x Vpk /10^6 = 0.006283 v/microsec
    http://en.wikipedia.org/wiki/Slew_rate

    so the problem is not slew rate. when I replace uA741 with "OPAMP" in pspice (which is ideal opamp) there is no distortion in the output. what do you think about the reason of this kind of distortion?
     
  2. #12

    Expert

    Nov 30, 2010
    16,257
    6,757
    You already found the answer. Changing the op-amp fixed the problem, so what was the problem?

    The 741 is almost the oldest op-amp known to man. Any IC that has been through 40 years of improvement will work better.
     
    Last edited: Oct 20, 2013
  3. PersianEngineer

    Thread Starter New Member

    Aug 15, 2013
    19
    0
    [​IMG]

    Output for 1kHz sine wave
    [​IMG]
    Output for 10kHz sine wave
    [​IMG]
     
  4. crutschow

    Expert

    Mar 14, 2008
    12,991
    3,226
    The 741 is not an audio power amp, it is an op amp with very limited output drive capability (2kΩ nominal minimum load). It cannot drive an 8Ω speaker load. What makes you think it could? The ideal op amp has no such limitation, so it will work.

    Where did you get that circuit? It appears to be designed for an audio amp with a single power supply but you have a dual supply.
     
    Last edited: Oct 21, 2013
    PersianEngineer likes this.
  5. LvW

    Active Member

    Jun 13, 2013
    674
    100
    *Your slew rate calculation is not correct.
    *Resistors R1 and R2 are needed for single supply only (as mentioned by Chrutschov)
     
  6. PersianEngineer

    Thread Starter New Member

    Aug 15, 2013
    19
    0
    What is the role of R3, C2 and C4 in the above circuit?
     
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