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Airline headphone conversion

Discussion in 'Electronics & Electrics' started by methodMAN, Oct 11, 2018.

  1. methodMAN

    methodMAN Member

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    hey,

    Picked up these Emirates noise cancelling headphones brand new at a swap and sell in a bundle with some other stuff for $15 total.

    So now onto getting them to work.

    From a quick google it looks quite do-able and I do have the skills (can solder and sparky by trade).

    1. What voltage and polarity of the pins is required for the noise cancelling to work?
    2. Is there a easier way than what is shown as the instructable is pretty old?

    cheers

    mM

    [​IMG]

    [​IMG]
     
    Last edited: Oct 11, 2018
  2. slavewone

    slavewone Member

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    Hmm, I’d say it needs power to work at all. Try it with 1 or 2 or 3 batteries.

    I’m guessing a 3.5mm stereo to dual mono adapter should work to bring both channels together for easy.
     
  3. merlin13

    merlin13 Member

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    Yup, the audio will will be merely a stereo Left/Right/Gnd bog-stock 3.5mm plug, assuming you want to mod this back to "normal" headphone use".

    Being noise cancelling it'll need power, and unless it's marked on it somewhere and/or someone gets the right answer from Uncle Google actual voltage/current rating will be somewhat of an unknown - assume mebbe half amp or so, but could be 5 volt, could be well over 5 volt (6, 8, 9, 12, 15... pick one, any one, Tune For Maximum Smoke If You Get It Wrong...).

    "Probably" Centre Positive but You Never Never Know on that nowadays...
     
  4. ipv6ready

    ipv6ready Member

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    Google is your friend....

    PS: I didnt watch any of it, other than first 10seconds.
     
  5. kombiman

    kombiman Dis-Member

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    Have a look at the board on the other end, ther'll be red and black and maybe some markings re voltage
     
  6. OP
    OP
    methodMAN

    methodMAN Member

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    So....

    after connecting it up as per the connections when I dismantled the headphones...

    and trying 4.5V (3x1.5V) 6V (4x1.5) and a 9V battery

    NOTHING!!!! SWEET NOTHING

    The red led indicator comes on at all voltages, and that is it.

    So I googled some more and reddit has this:

    In order for the noise cancellation to work, the microphones require a bias voltage (power), which comes from the noise cancellation circuitry located in the jack in the armrest. Without that circuitry powering the microphones, and the active noise cancellation circuit in the jack, these headphones have no noise cancellation capability, and are just like regular wired headphones. Although they have extra acoustic design/foam inside.

    Source: I worked on these headphones, improving the acoustics, building the smartjack, and designed the production and maintenance equipment used for testing the noise cancellation performance.


    Seems a bit over the top and excessive - but it may just be the case.

    I don't get any audio, so they could just be stuffed.

    May try a power pack and a voltage regulator thingy to see if it needs more grunt. Maybe 12V.....

    cheers

    mM

    [​IMG]
     
  7. ipv6ready

    ipv6ready Member

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    ^^
    The extra cost for over engineered ciruitary to stop the headphones being simply rewired would definitely be worth it for the airline.

    Could you imagine if it was a simple matter of rewiring and supplying power to make them fully functioning noise cancelling headphones how many of these headphone would walk off the plane.

    In fact if it was just matter of re wiring I’d bet eBay and Amazon would be full of simple plug in converters with battery pack that could be used without cutting the cable.
     
    kombiman likes this.
  8. mtma

    mtma Member

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    From what images I can gather, what's actually inside the cups is pretty crude. The bias is probably for the condenser microphones and the LED actually is not for anybody to look at but the cheapest way to anchor the microphone bias voltage at roughly 3V.

    Does anyone have a trace out of the circuit on the board? Would be definitive in determining how much smoke and mirrors is going on here...
     
  9. OP
    OP
    methodMAN

    methodMAN Member

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  10. _zak

    _zak Member

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    Can you follow the traces from VDD- and VDD+? Which chip do they go to?
     
  11. merlin13

    merlin13 Member

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    Those low power amp chips are spec'd to run 'tween 2 and 16 volts Vcc.

    But I wouldn't go anything right up in case you bork the microphones, 'specially as tickling Uncle Google those headphones seem to be able to work with 3 to 5 volts on the power in/jack at bugger-all amp rating.

    Exactly (!) how are you connecting everything up and what audio source are you using?
     
  12. mtma

    mtma Member

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    Uncle Google shows a different model.

    On quick inspection whoever drew the PCB liked alignment so things are actually positioned for looks over function and the silkscreen between the SMD components covers up the exact traces between them, but it looks like it is pretty much an active cancellation circuit. A bit of trivia is that pattern of the two amplifiers are rotationally symmetrical. So if you can power up the amps it should work.

    Attached is a doctored image to make retracing without the actual thing easier for anybody who wants to play.
     

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  13. OP
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    methodMAN

    methodMAN Member

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    THEY WORK!!!

    had to stop by jaycar for some other bits and pieces so I grabbed a female stereo jack.

    I soldered that onto the headphone wires and used a male-to-male cable and 4.5V (3x1.5V AA Batts) and it works.

    Why....... I don't know????

    I had checked and buzzed out all my connections previously and it was all good.

    I had tried 2 different 3.5mm male plugs I cut off working earphones.

    When you turn the headphone power off you do hear a difference in the sound quality, but if you didn't have the power (noise cancelling option) they sound fine and you would not know the difference to the avg human ear.

    Will do some more testing, and make pretty and put it all in a case and post pics.

    cheers

    mM
     
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