need help with opamp

Discussion in 'The Projects Forum' started by doors666, Sep 21, 2014.

  1. doors666

    Thread Starter New Member

    Mar 21, 2014
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    i am trying to make a cmoy like headphone amp using ne5532 (thats all i have at hand in duals at present, might replace later). power right now is from 7815/7915. I am using r2=27k, r3=33k, r4=150k. Load is a 330R resistor. Ckt is here. Cap is presently 0.1uf for testing, will increase it later. ckt is on breadboard.I am giving a single channel an output from a sig gen. Similar ckt worked fine in ltspice.


    Output pic is attached. Blue is input and red is output. Could someone please tell me why is it coming like this and how do i fix this.
     
  2. #12

    Expert

    Nov 30, 2010
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    Output sag is caused by too small of a capacitor.

    ps, this chip only promises to drive a 600 ohm load.
     
    Last edited: Sep 21, 2014
  3. MikeML

    AAC Fanatic!

    Oct 2, 2009
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    The reactance of the output coupling cap at the lowest audio frequency you want to pass must be small compared to the load resistance...
     
  4. doors666

    Thread Starter New Member

    Mar 21, 2014
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    I changed the cap to 1uf (its input cap, not output), it works fine now.

    What should be the min input impedance of a headphone amp. Currently I am using 27k resistor and i suspect it might be too low.
     
  5. #12

    Expert

    Nov 30, 2010
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    1) What is driving the input?

    Non-inverting...you can make the impedance really high if you need to.
    The volume control shown on the pdf is 10k which is worse than 27k.
    Back to: What is driving the input?

    A headphone amp? or am I reading too fast?

    I mean, a crystal radio would want a million ohms. An MP3 player might work into 16 ohms.
     
  6. doors666

    Thread Starter New Member

    Mar 21, 2014
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    the usual suspects, cd player, ipod, phone or pc/laptop driving my headphone amp, most of the usage will be portable.

    I am not planning to use a volume control. Source will control the volume.
     
  7. bertus

    Administrator

    Apr 5, 2008
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