OP AMPS - Crossover distortion

Discussion in 'The Projects Forum' started by missfangula, Oct 19, 2010.

  1. missfangula

    Thread Starter New Member

    Sep 14, 2010
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    Hi,

    Can someone please explain to me how op amps eliminate crossover distortion?

    Thanks,
    miss fangula
     
  2. R!f@@

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    Apr 2, 2009
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    OP amps does not introduce cross over distortion in the first place.

    Amplifiers classes other than class A produces cross over from it's output stage.

    So a google search and read. U'll know better this way
     
    Last edited: Oct 19, 2010
  3. Ron H

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    LM324/358, etc., has a class B output stage, and will create crossover distortion if used with dual supplies and a grounded load.

    Op amps reduce crossover distortion, with feedback, because the high open loop gain forces the output to do what it needs to to keep the voltage difference between the inputs near zero.
     
    Last edited: Oct 19, 2010
  4. R!f@@

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    I know tht power OPAMPS have been introduced with class B out put stage.
    I was right tht the output stage introduces distortion
     
  5. Audioguru

    New Member

    Dec 20, 2007
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    No.
    The LM358 dual opamp and the LM324 quad opamp are the first "low power" opamps. They reduce their supply power by operating the output transistors in class-B with hardly any bias current instead of in class-AB that has enough bias current to avoid crossover distortion. The class-B opamps have 3% of crossover distortion even with plenty of negative feedback and ordinary class-AB opamps have 0.003% or less distortion (one thousand times less distortion).

    No.
    The TL07x opamps have 0.003% distortion and the OPAx134 opamps have 0.00008% distortion. Their output transistors operate in class-AB.
    I don't know any opamp that operates the output in class-A. It would melt.

    Class-A amplifiers heat the entire neighbourhood even when they are doing nothing.
     
  6. Ron H

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    My point was that LM324/LM358 are op amps. They are not power op amps.
     
  7. Audioguru

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    Dec 20, 2007
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    No.
    The lousy old LM358 and LM324 have such poor high frequency response that negative feedback cannot reduce the crossover distortion much.
    Crossover distortion is at fairly high audio frequencies where their gain and slew rate are low.
     
  8. Ron H

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    I wrote:
    My reply about op amps reducing crossover distortion was intended to answer the OP's question:
    My answer is generally true, but not for all op amps across the audio range. The OP said "eliminate". I changed that to "reduce" in my reply.
    I only used LM324/358 as an example of an op amp with internal crossover distortion, and illustrated with a simulation how it reduces internal crossover distortion at low frequencies. I never implied that these op amps were good for audio.
     
  9. Audioguru

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    The crossover distortion is as high as 3% with negative feedback.
    I wonder how high it is without negative feedback. 20%? 40%?
    Those lousy old opamps should be buried.
     
  10. R!f@@

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    What are u trying to prove..opamps are not the one introducing distortion.

    the output stage does. Proper biasing minimizes crossover. It never is eliminated.

    Even at 0.003% there is distortion. It does not eliminate.

    U all are saying cross over. So is the opamp introducing crossover or it's output stage.
    Power or no power OPAMP. Class A has NO cross over distortion.

    Others even at 0.0000000000000001% crossover distortion.

    It is distortion. Difference is it's not measurable or audible.

    Audioguru
    U said No so many times tht u forgot what it was being said.

    Class A has NO distortion.
    Everything else has Distortion.

    U cannot prove otherwise.

    U say NO and u prove ur self wrong.
     
  11. Ron H

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    I don't disagree with you, except that LM324 is an op amp. The output stage is an integral part of it.
     
  12. R!f@@

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    By the way.. what does negative feedback has to do with crossover.

    I thought feedback is used to stabilize the gain and bandwidth of a typical amp.

    Guru is confused with crossover and feedback.
    How long have u been a guru in Audio.
    I think Ur nick precedes you
     
  13. R!f@@

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    Ron, It's not u I am referring to...what U said is true and I agree.

    But I do not agree with the Guru
     
  14. Audioguru

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    A few people can hear 0.1% crossover distortion but they cannot hear the 0.003% total distortion from many opamps.
    Class-A is a heater, not an amplifier. A class-A amplifier has even-harmonics distortion. A class-AB amplifier cancels most even harmonics distortion.
    Most amplifiers are cool class-AB and their tiny amount of distortion cannot be heard.
     
  15. R!f@@

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    By the way....Class A won't melt at low power and pre-drive stages.

    Even at moderate power It works. I have built it and to drive a high frequency to it's best, this is the way to go.
    I always prefer class A pre- drive stage to ELIMINATE crossover at this point.

    Guru. U are not the only one who built Power amps and is familiar with it's varieties and heating effects
     
  16. R!f@@

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    AAAH! Now u are getting my point. :)

    We are not talking about individual hearing capability.
    We were talking about OPAMP eliminating cross-over.

    It minimizes. It never eliminates.
    Hearing it is totally different.
     
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