Mono signal to stereo headphones output

Discussion in 'The Projects Forum' started by paulsoulsby, Jul 11, 2013.

  1. paulsoulsby

    Thread Starter New Member

    Jan 9, 2013
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    0
    Hi,

    I have a mono source which I need to output to a mono line level output and also to stereo heaphones.

    I have looked online for stereo headphone op-amp circuits and they all use 2 opamps (because normally the source would be stereo).

    I only have 1 opamp left on my IC and am loathed to break into another, especially when my source is mono.

    At the moment I am just splitting the output of the opamp and sending each branch through a 16 ohm resister and 220uF capacitor.

    Is this OK? I'm guessing it may not be. I realise you can't just tie the left and right channel of the headphones together, as you would be essentially creating a much smaller load, as both headphones would be in parallel.

    Should I adjust my output resister and capacitor values?

    Here's the circuit, with the loads shown as resistors.

    [​IMG]

    thanks
    Paul
     
  2. MrChips

    Moderator

    Oct 2, 2009
    12,440
    3,361
    The plug for stereo headphones are wired with Left and Right channels plus Common.
    For mono, use the L and R signals and ignore the common.
    This will give you twice the impedance.

    The head phones will be driven out of phase but your ears will not tell the difference.
     
  3. paulsoulsby

    Thread Starter New Member

    Jan 9, 2013
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    0
    Hmm, that's a cunning trick, but I think you would be able to hear that it's out of phase. When audio is 180° out of phase, it sounds as though its behind you, which would be a problem in my project.
    Ideally I just need to split the signal to both headphones and keep the output impedance matched.
     
  4. wayneh

    Expert

    Sep 9, 2010
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    Not in headphones, I think. There's no issue of the out-of-phase waves hitting the same ear.
     
  5. kubeek

    AAC Fanatic!

    Sep 20, 2005
    4,670
    804
    It works in headphones too, the out-of-phase sound is really uncomfortable.
     
  6. MrChips

    Moderator

    Oct 2, 2009
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    I'm doing it right now with headphones for my crystal radio. I can't tell any difference.
     
  7. wayneh

    Expert

    Sep 9, 2010
    12,119
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    My hunch was wrong and kubeek's observation is shared by many others. Human hearing is pretty amazing.
     
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