Understanding Headphone-Jack Circuitry

Discussion in 'The Projects Forum' started by phnord, May 29, 2013.

  1. phnord

    Thread Starter New Member

    May 29, 2013
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    I'm trying to get a better understanding of how the circuitry of a headphone jack works for a project I'm building. Here's where I'm confused.

    From what I understand, a standard TRS jack carrying stereo audio will have the the Tip carry the left audio, the Ring carry the right audio and the Sleeve act as a shield. It is also my understanding that the audio carried along the first two is comprised of basically an alternating current that is representative in its frequency of the audio signal.

    Now here's where my confusion is... wouldn't each channel need not one but two wires in order to make a complete circuit? And if not, how can the electricity flow without a complete circuit?

    Keep in mind I am just now revisiting the topic of electronics; for all intents and purposes, assume that I have no prior knowledge of circuitry outside of how a battery powers a lightbulb.

    Thank you!

    - Andy :)
     
  2. Trimalchio

    New Member

    May 3, 2013
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    Yes, each channel/phone does need two connections (whether it's ac or dc), but one connection on each can be shared by both channels - what you call the "shield" is the shared second connection for both channels. So you need just three wires - 1) left signal wire; 2)right signal wire; 3) shared left & right signal return wire (usually grounded).
     
  3. phnord

    Thread Starter New Member

    May 29, 2013
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    0
    Thank you, trimalchio - that's very helpful.

    I'm still struggling a little with some basic concepts regarding circuitry, voltage, current and grounding. If either you or someone else would help shed some light on this for me, I would greatly appreciate it.

    In the example of a battery with a lightbulb wired to it, my understanding is that the + side of the battery contains a positive charge, the - a negative charge, and when these two ends are connected the electrons will want to flow from the negative end to the positive end in order to even out the charge. As they do so, they pass through the lightbulb filament and the resistance of that filament converts some of the energy into light, making the lightbulb glow.

    Now... my understanding is that "ground" refers to a reference voltage in a circuit, and is commonly the reference voltage of the Earth (hence the name "ground"). Am I to understand that in a headphone circuit (let's simplify this to a mono, Tip / Sleeve situation), the Tip is charged alternately positively and negatively in relation to the ground, causing the electrons to either be pulled from or to the ground and pulsating the speaker along the way?

    And if this is correct... then why would the aforementioned lightbulb circuit need to be wired to both the positive and negative ends of a battery? Couldn't you, say, wire the end that would normally connect to the - terminal to a ground instead, and then wouldn't the + end's positive charge cause electrons to be pulled from the ground? Or for that matter vice-a-versa -- wire the end that would normally be wired to the + end to the ground, and let the electrons flow from the - end out through the bulb?
     
  4. #12

    Expert

    Nov 30, 2010
    16,262
    6,769
    Ground is just a word of convenience. Often, it doesn't mean Planet Earth Ground, it just means, "common" to both circuits.
    Here's a drawing of 2 same-as-each-other circuits.
     
    Last edited: May 29, 2013
  5. Trimalchio

    New Member

    May 3, 2013
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