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741 circuit amp wont turn on

Discussion in 'General Electronics Discussion' started by Jeorge, Oct 31, 2016.

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  1. Jeorge


    Oct 31, 2016
    I have built a small amp circuit with a light in the circuit. But the light wont turn on and no power is going through the board. I have used different types of rechargeable and normal non rechargeable 9v batteries, but still no power. My amp circuit is made up of a resistor, capacitor and 741 op amp.

    Any help and advice would be appreciated.
  2. hevans1944

    hevans1944 Hop - AC8NS

    Jun 21, 2012
    Post a schematic. Draw it on paper if you have to and take a picture.
  3. Jeorge


    Oct 31, 2016
    Heres my drawn schematic.....Hope it makes sense.

    Last edited by a moderator: Oct 31, 2016
  4. davenn

    davenn Moderator

    Sep 5, 2009
    as drawn, no it wont work

    you have a capacitor in line with the input, why? is there a DC or AC voltage going in there ?
    you have a capacitor in line with the lamp, again, why ? do you know DC doesn't go through a capacitor ?

    you have the lamp going back to the non inverting input ( the + input), this is incorrect the + input, the lamp should be going to 0V
    when pin 4 of the op-amp is going to
    ohhh and you have pin 4 marked as 9V instead of 0V

    Arouse1973 likes this.
  5. Herschel Peeler

    Herschel Peeler

    Feb 21, 2016
    What does it take to light the lamp? Voltage? Current?
    The LM741 can't put out much current. And the more current you draw the lower the output voltage.
    What voltage in?
    Try it without the capacitors.
  6. BobK


    Jan 5, 2010
    No, this will never work, even without the capacitors. The input pins cannot source or sink current, and that is what your circuit is expecting.

    How about telling us what you are trying to do. I cannot determine that from the totally flawed schematic that you posted.

  7. Audioguru


    Sep 24, 2016
    I suspect that he wants the light bulb to light up when there is a low level AC signal at the input. Then a properly biased amplifying opamp van drive a rectifier/filter circuit that drives the light bulb.

    The datasheet for a 48 years old 741 opamp says that its non-inverting input pin3 will not work if it is within a few volts from ground but here it is at ground.

    The incandescent light bulb has no voltage or current rating. If its part number was shown then we could look them up.
  8. davenn

    davenn Moderator

    Sep 5, 2009
    Thread is closed
    till the OP responds to me


    please PM me if you understood what was commented on and you have further info to add
    and I can reopen the thread

    hevans1944 and bushtech like this.
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