Switching audio ON/OFF in headphones

Discussion in 'General Electronics Chat' started by surfline, Apr 11, 2010.

  1. surfline

    Thread Starter Active Member

    Aug 12, 2009
    30
    0
    Hi,

    I was trying to put a toggle switch in series on the GND line in my headphone wires in order to be able to manually switch the music on / off. Through doing this, I noticed that the audio would still play when the GND was not connected / open circuit. I was puzzled by this, the volume was still at a decent level even open circuited. I have a left channel and right channel wire as well in my head phones.

    I now know that I need to switch the right and left audio channel wires in order to achieve my goal, however I was just wondering the explanation of the audio circuit still working without the ground completing the circuit.

    Thanks.
     
  2. Ghar

    Active Member

    Mar 8, 2010
    655
    72
    Since both channels are sharing the ground they are actually connected together.
    The left signal wire will use the right signal wire as a return and vice versa.
     
  3. Bychon

    Member

    Mar 12, 2010
    469
    41
    More pacifically, the sound in the headphones will be the difference between the two channels. Because, if both channels are outputting 1 volt, the difference of voltage across the speakers will be zero. If one channel is outputting one volt and the other channel is outputting negative one volt, the difference across the speakers will be 2 volts.
     
  4. Ghar

    Active Member

    Mar 8, 2010
    655
    72
    Just for fun I simulated two emitter-follower stages driving two speakers, with and without the ground wire.

    Here's the plot of voltages across the loads:
    left-right.png

    The green lines are with the ground wire, the red lines are without.
    Top plot is the first channel and the bottom is the second.
    I made the two signals slightly different in frequency and amplitude so you can tell them apart.
    As you can see, Bychon is spot on about the result being the difference between the original signals.

    With equal load resistances the voltages (red line) are actually the same but inverted.
     
  5. surfline

    Thread Starter Active Member

    Aug 12, 2009
    30
    0
    Ah, I see. Makes sense. Thanks for the help.
     
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