creating a offset voltage on a inverting amplifier

Discussion in 'The Projects Forum' started by djstar, Nov 21, 2014.

  1. djstar

    Thread Starter Active Member

    Jan 26, 2008
    I am trying to create a audio amplifier that runs from a single supply. fundamentally i need to create a high gain amplifier of around 1900 Av with a bandwidth of 400 to 400KHz with a defined input impedance of 50K and i have to use 741 op amps the inpout signal is around 1mV-10mV.

    Ive decided to create a LPF with one op amp and then connect it to a HPF through another opamp, which will give me the gain and bandwith.

    as the signal coming in is +/- 1mv i want to create a 5V DC bias that the signal will ride on. however i'm struggling to get the amplifier to work.. i have attached two showing the amplifier with the non inverting pin ground, this gives a output signal of around 0.2V with the negative part of the signal clipping which is what i expect. when i set a dc voltage of 5V on the non inverting pin i get a flat response?

    for the time being i have left of the Cap on the feedback resistor which would create the LPF.
  2. Dodgydave

    Distinguished Member

    Jun 22, 2012
    Last edited: Nov 22, 2014
  3. DickCappels


    Aug 21, 2008
    Hint: You are starting with the wrong op-amp. Check out the app note Dodgydave recommends.
  4. BobTPH

    Active Member

    Jun 5, 2013
    At 400KHz, the 741 has an open loop gain of 2.5. It is totally useless for what you are doing.

    And why would a audio amplifier go up to 400KHz anyway?

    RamaD and #12 like this.
  5. #12


    Nov 30, 2010
    I was working on that yesterday. I came up with, "You will need 76 chips to do this". Then I doubted myself and erased it. :oops:

    Thanks for being more succinct than I could manage that day.
    BobTPH and atferrari like this.