Op-Amp Circuit

Discussion in 'General Electronics Chat' started by electrical_ck, Apr 29, 2010.

  1. electrical_ck

    Thread Starter New Member

    Dec 7, 2009
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    I designed a multistage amplifier circuit to meet my needs of have a load of 20 ohms, a gain of 200 and a input resistance of 150k. I used a CC-Common Emitter with partial bypass (gain of 10), another CE w/partial bypass (gain of 20), and a CC at the end. I did all my calculations and I got my circuit doing everything I wanted on multisim. My questions is how could I downsize this circuit with using an op-amp(741), I built another circuit on multisim that gets me my gain of 200 with using an non-inverting design, my key issue is since i need a input resistance of 150k, I know that op-amps have very high input resistance, I just don't understand if the second circuit is good enough since its input resistance is much much higher then the 150k.
     
  2. hgmjr

    Moderator

    Jan 28, 2005
    9,030
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    What is the operational frequency range requirements of your amplifer?

    hgmjr
     
  3. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    I don't see your circuits. Please post images of them using the "Go Advanced" and "Manage Attachment" buttons. .png format is preferred.

    741 opamps are 40 years old, non-linear, and woefully obsolete. A TL071, 72, 74 opamp would be a far better choice, although there are many that are much better.
     
  4. electrical_ck

    Thread Starter New Member

    Dec 7, 2009
    10
    0
    thanks for the quick, reply I will use a different op-amp, the circuit attached is my 4 stage circuit.
     
  5. SgtWookie

    Expert

    Jul 17, 2007
    22,182
    1,728
    Take a look at using a TL072 as a 2-stage preamp, and then use an audio amplifier IC for the output stage.

    If you try to amplify the signal too much in one stage, you will have a rolloff in your higher frequency response.

    Look at the datasheet for the TL072. Notice it's gain bandwidth product. Use that as your guide as to how much to amplify in one stage.
     
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