audio amplifer

Discussion in 'The Projects Forum' started by JasonL, Jun 17, 2013.

  1. JasonL

    Thread Starter Member

    Jul 1, 2011
    I recently finished courses that covered op amps, capacitors, and inductors.

    I learned how to calculate the gain of an ideal op amp using nodal equations.
    I learned how to write transfer functions in circuits with capacitors and inductors by writing nodal equations in S-domain.
    I learned how to determine what type of filter the circuit is from the transfer function.

    I want to create an audio amplifier for mp3 player that will power a small speaker.

    I started simple and created a simple op amp. The circuit is attached. The circuit gets louder as R2 > R1 but there is a lot of distortion. The course I took at my university so far taught how to analyze a circuit and write equations, but I have no experience the other way around (i.e to design one).

    What would I need to do to make the output sound less distorted. I know I would probably need a capacitor or inductor somewhere but how do I know where to put it? And I'm guessing the next step would be to write a transfer function and solve for the component value?
  2. bountyhunter

    Well-Known Member

    Sep 7, 2009
    The understanding that an op amp can't drive a speaker. An op amp's output impedance is probably 100 Ohms and you are trying to drive a load which is probably 8 Ohms or 4 Ohms. Can't work.

    Power amps that drive speakers have an output impedance om maybe a tenth of an Ohm.
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  3. Shagas

    Active Member

    May 13, 2013
    As bounty said , a normal OP amp can't provide enough current to drive an 8 ohm speaker. Try putting a 30--80 ohm resistor in series with the speaker depending on your voltage. It will be playing at a much lower volume but undistorted
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  4. Dodgydave

    Distinguished Member

    Jun 22, 2012
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  5. crutschow


    Mar 14, 2008
    Unfortunately, they don't seem to teach how to read a data sheet in school. :rolleyes: If you look at that for the 741 you will see that it can typically deliver only a few mA into a load. You need an audio amp, such as Dodgydave suggested.
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  6. tracecom

    AAC Fanatic!

    Apr 16, 2010
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