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Thread: What are the Line OUT pins on Audio Adaptor Board Teensy 3.x for?

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    What are the Line OUT pins on Audio Adaptor Board Teensy 3.x for?

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    The audio board comes with a 3.5 audio jack connector to connect speakers, or a headphone. Now, what can I connect to Line Out pins ? What is the difference between the Line Out pins and the 3.5 audio jack connector. Please, explain.


    Thanks, very much

  2. #2
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    The 3.5mm audio jack is for headphones or earphones only, it is not able to drive a typical speaker impedance
    without overloading, only down to a minimum of 16 ohms. The output power from the headphone channels is
    62mW only, inadequate for a speaker.

    Note the headphone jack "ground" is not ground, and should never be connected to ground as it has a DC offset,
    meaning that trying to use the jack as line-outs could lead to damage in some situations.

    The line outs are the outputs for further signal handling, such as connecting to an audio amplifier for driving
    speakers. The audio shield has DC-blocking capacitors on these lines so they are ac only.

    "Line level" signals are what are used in audio for moving analog signals around between equipment such as
    preamps and amps. The SGTL5000 maxes out at about 1Vrms on all outputs, note. Line level signals normally
    expect to see load impedances of 10k or higher.

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    Thanks very much and I am very glad I asked. To further understand the use of this sound card how what factors limit the maximum output power this sound card? Thanks.

  4. #4
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    The SGTL5000 datasheet is where all the information for it is. Line outs are not for power, they are signal level.

  5. #5
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by hbtousa View Post
    What is the difference between the Line Out pins and the 3.5 audio jack connector.
    There are 3 main differences.

    1: headphone output has an amplifier capable of driving headphones (but not speakers)

    2: headphone has digital volume control

    3: line out is ground referenced, where headphone has a virtual ground

    The line out is meant to send audio to other equipment like a AV receiver or power amplifier. That other gear is meant to have the volume control. The term "line out" is commonly used in audio equipment for this type of audio signal meant to connect between audio components.

    The headphone output is meant for plugging in headphones. It is not capable of driving speakers.

  6. #6
    Quote Originally Posted by PaulStoffregen View Post
    The headphone output is meant for plugging in headphones. It is not capable of driving speakers.
    However note that the headphone jack can drive this kind of thing:

    https://www.amazon.co.uk/gp/product/...?ie=UTF8&psc=1

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    that is an audio to Bluetooth transmitter. If you have some kind of amplified Bluetooth speaker (for example I use the soundbar under my TV) then this happily transmits Teensy audio to it from the headphone jack. Because of mobile phones I'm guessing most folks have some kind of bluetooth audio device in the home? It also works well with my Sony WH-CH700N bluetooth headphones too.

  7. #7
    Senior Member+ MichaelMeissner's Avatar
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    And there are low powered speakers that are meant to be plugged into a headphone jack. The speakers typically have a battery and USB power support. I've seen them called 'bomb' speakers or 'hamburger' speakers.

  8. #8
    Senior Member+ Frank B's Avatar
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    I think you must make sure they will be not connected anyhow to the "correct" ground.. otherwise there will be a problem which can kill hw.

  9. #9
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    Yes, unless you have isolated (ie battery powered) speakers do not use the headphone socket, use the line-outs only. A battery powered
    speaker with the charging lead connected is not always isolated, note.

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