MBA 3.5" audio power in mWatts ?

Discussion in 'MacBook Air' started by macbedhead, May 9, 2014.

  1. macbedhead, May 9, 2014
    Last edited: May 10, 2014

    macbedhead macrumors member

    Joined:
    Jun 28, 2010
    #1
    Hi, does anyone know how many mWatts the MBA can give out of the 3.5mm earphone socket ?

    I'm guessing it may be 300mWatts (approx 1/3 of 1 watt total to both ears) max ?
     
  2. checkitout, May 10, 2014
    Last edited: May 10, 2014

    checkitout macrumors member

    Joined:
    Nov 2, 2009
    #2
    Couldn’t find a datasheet for the CS4208, but this data sheet for the similar CS4207 says:

    Headphone Amplifier
    – GND Centered
    – Integrated Negative-voltage Regulator
    – No DC-blocking Capacitor Required
    – 50 mW Power/Channel into 16 Ω

    So it’s probably on the order of 100 mW total, *if* you have a matching 16 Ω load. Derate for non-matching loads.

    Edit: looked closer. There are two values that are possible for the supply voltage: 5 V or 3.3 V; I don’t know which one Apple chose. Depending on the distortion you find acceptable, page 17 gives:

    (First number @ 5V, second number @3.3 V)
    Output Power, THD+N = -75 dB, RL = 16 Ω: - 38 -, - 17 - mWrms
    Output Power, THD+N = 1%, RL = 16 Ω: - 50 -, - 23 - mWrms
    Output Power, THD+N = 10%, RL = 16 Ω: - 74 -; - 35 - mWrms

    So depending on your tolerance for distortion and the circuitry that Apple chose, the total is somewhere between 34 and 148 mW for both channels (16 Ω load). If the CS4208 is anything like the CS4207.

    Oh, and some actual measurements! He gets 45 mW (per channel, apparently) @ 32 Ω.
     
  3. macbedhead thread starter macrumors member

    Joined:
    Jun 28, 2010
    #3
    That is suprising !

    I'm using planar magnetic headphones that are 50ohms and they can take up to 3000mWatts (3 watts) and yet they drive to about 70% sound quality/volume of my desktop headphone amp out of the Air when I'm mobile.

    I was just worried I may be taxing something on the logic board by drawing the power straight off the Air vs a portable headphone amp. Of course the battery goes down faster but not too bad considering.
     
  4. Mrbobb macrumors 601

    Joined:
    Aug 27, 2012
    #4
    Taxing the Air??? As long as u don't use any 4 ohms phones nothing will happen.
     

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