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Amplifier Specs

Discussion in 'Electronic Design' started by Hoektoe, Aug 17, 2007.

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  1. Hoektoe

    Hoektoe Guest

    Can somebody please tell me how to calculate the power output of a
    class AB power amp.
    If the amp supply has a +-60V swing, do you use 60V or 120V in the
    power calculations?
  2. Phil Allison

    Phil Allison Guest


    ** Depends on the method of calculation of course.

    A sine wave has a ratio of peak to rms of 0.7071

    It also has a ratio of rms to peak to peak of 2.83

    Power depend on the load resistance too.

    Then maybe YOU are after peak power or music power or PMPO power or ****
    knows what power.

    Got the faintest clue what you are on about ??

    ........ Phil
  3. Tam/WB2TT

    Tam/WB2TT Guest

    Either, but using 60V is more convenient. P=Vrms**2/R. So for +/- 60 V swing
    Vrms =60/SQRT(2) = 42.4V.
    Now, for an 8 Ohm load, power will be (42.4 **2) / 8 = 225W. You won't
    actually get that much out because the voltage won't quite go to 60 V. 58
    might be a reasonable guess.

  4. Fred Bloggs

    Fred Bloggs Guest

    If the output swing is 60V above and below a DC of 0, please explain at
    what point in time the load would ever see 120V?
  5. D from BC

    D from BC Guest

    How about just make up your own power spec...
    How about...
    The max power handling of the amp is the heat dissipated by the
    speakers when you almost hear distortion when playing your favorite

    (Assuming the speakers don't distort first.)

    D from BC
  6. Rich Grise

    Rich Grise Guest

    Apparently, they haven't covered "peak-to-peak" in class yet. ;-)

  7. Eeyore

    Eeyore Guest

    58V would be pretty good actually. Allowing a Vce of 2V would be reasonable but
    there'll be an IR drop in any emitter resistor too. A typical value would be 0.3
    ohms and with around 7A peak of load current, you'll lose another 2V there too.

    And the really huge variable is power supply regulation. Audio power amps are
    not normally operated from regulated supplies. Power supply 'sag' on load of 10V
    would be quite normal..

    All of the above would bring the full power down to ~ 150W.

  8. Charles

    Charles Guest

    Assuming a sine wave, Vp = Vp-p/2 and Vrms = Vp x 0.707
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