problem in multistage amplifier

Discussion in 'The Projects Forum' started by refat, Sep 17, 2012.

  1. refat

    Thread Starter New Member

    Sep 16, 2012
    7
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    hello Everyone,
    I am working on my project (multistage common Emitter amplifier) and am stuck with problem her when input signal from signal generator.......
    no any amplifier signal in output........... is there any problem in the design of this amplifier???????!!!!!





    [​IMG]
     
  2. MrChips

    Moderator

    Oct 2, 2009
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    Put a capacitor between the signal generator and the input of the amplifier to block DC voltage.
     
  3. refat

    Thread Starter New Member

    Sep 16, 2012
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    0

    thank u MrChips.....
    also no amplifier output signal when i put a capacitor between the signal generator and the input of this amplifier.
     
  4. MrChips

    Moderator

    Oct 2, 2009
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    What transistors are you using?
    Check that the transistors and all other components are connected correctly.
     
  5. refat

    Thread Starter New Member

    Sep 16, 2012
    7
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    please any one .....
    help me....... design this amplifier on any Electronic simulation program like Circuit Wizard or multisim.....etc
    or by any calculation to check this amplifier.....
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    Guess you didn't like my advice.
     
  7. refat

    Thread Starter New Member

    Sep 16, 2012
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    i used in this project - npn - transistors Bc107
    all components are 100% connected
     
  8. akis02

    Member

    Apr 30, 2011
    57
    3
    Circuit will not work as is.

    1) Remove the 100uF and the 200uF caps.
    2) Remove the 2.2K between the two transistors - just connect the capacitor
    3) on the second transistor replace the 10K with a 22K and the 2.2K with a 4.7K.
    4) on the first transistor replace the 39K with a 100K and the 10K with a 33K.
     
  9. ScottWang

    Moderator

    Aug 23, 2012
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  10. absf

    Senior Member

    Dec 29, 2010
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    I tried your circuit on proteus and I found out that if the input signal if >2mV (2000Hz sin wave), the output is severly distorted on the tops and bottoms.

    Below is the scope display comparing the input and output using a 10mV 2000Hz sin wave. The gain of the amplifier based on the scope amplitutde is roughly 1500.

    Allen
     
    Last edited: Sep 17, 2012
  11. Dodgydave

    Distinguished Member

    Jun 22, 2012
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    Looks like we have another idiot using software instead of building it on breadboard or Vero, like we did in my time.....:rolleyes:
     
  12. MrChips

    Moderator

    Oct 2, 2009
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    What are you trying to amplify?
    I tested the circuit on a breadboard and it works ok.
    The base bias may need slight tweaking. The two emitter bypass capacitors might be overkill. I used 10μF instead. You shouldn't notice much difference except at very low frequencies. I omitted the 2k2 series resistor.
     
  13. Audioguru

    New Member

    Dec 20, 2007
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    The transistors are biased properly so they should work.
    The emitters are both bypassed to ground so the voltage gain is very high.
    I calculated voltages. Measure the voltages of your circuit to see if your voltages are close.
     
  14. refat

    Thread Starter New Member

    Sep 16, 2012
    7
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    i want to:
    1- Input 1 kHz signal from signal generator and display input and output on an oscilloscope. Adjust input amplitude to avoid any distortion.
    2- Draw the input signal and the output signal and measure the amplitudes.
    3- Calculate the voltage gain of the amplifier from the results obtained in 2.
    4- Increase the input amplitude to a maximum value without causing significant distortion and record the value.
     
  15. refat

    Thread Starter New Member

    Sep 16, 2012
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    ok..... what about the resistor 2k2 (why u cancel this 2k2 )???
     
  16. MrChips

    Moderator

    Oct 2, 2009
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    So this is really a homework question.
     
  17. Audioguru

    New Member

    Dec 20, 2007
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    I reduced the values of some capacitors because high values are not needed.
    I simulated your amplifier using LTspice program.

    The amplifier produces noticable distortion at high output levels because it has no negative feedback.

    The 2.2k resistor is simply an attenuator that reduces the voltage gain.
     
  18. akis02

    Member

    Apr 30, 2011
    57
    3
    As we have said before (at least 4 of us), with the bypass capacitors in place, there is so much gain that it clips heavily with just 2mV input. If you remove the bypass capacitors then the gain falls to about 6x and then you will be able to see something meaningful on the scope. How can you practically reduce a 1mV signal so as to see a clean output on the scope? 1mV is like noise, you'll breathe the wrong way and get 1 mV.
     
  19. refat

    Thread Starter New Member

    Sep 16, 2012
    7
    0
    dddddd.................
     
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