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I have the Zoom G2.1Nu effects pedal. It has a 6.3mm mono out. I use a stereo adapter 6.3mm-to-3.5mm jack. Pedal is connected to the Mac via USB so the Mac's audio output is going through it.

I have a 2.1 sound system with some... ummm... control unit (here it is) and headphones.

So the question described below.

  1. Sound system (about $120) playing stereo sound from guitar (which has mono out), as well as from Mac.
  2. Some very cheap (about $10) headphones and sound systems also play stereo sound.
  3. Headphones (about $30) playing mono sound to the right channel from both sources even when connected to the 3.5mm out on any of those sound systems (though they are 100% working with stereo output from iPhone or Mac directly).

Why so?

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3  
According to the manual of your effects pedal, the output jack is stereo. –  NReilingh Aug 5 '13 at 1:06
    
@NReilingh Wow, thx, that makes sense. But what could be wrong then with the headphone's connector? –  efpies Aug 5 '13 at 9:50
    
Does your $30 set of headphones have a built in mic? The jack for that would have an additional connector. Mac devices are designed to deal with that. I don't think this would cause the problem but something to consider. I would suggest giving more specifics about the headphones that don't work and to try a third pair. –  Basstickler Aug 5 '13 at 23:29
    
This question appears to be off-topic because it is about audio production techniques and equipment. –  American Luke Aug 11 '13 at 1:38

2 Answers 2

To take your points directly:

  1. The sound system is not playing stereo out. It is playing mono through both speakers (very different to stereo)
  2. Sure
  3. The wiring for mono and stereo jacks is different, with the mono having a single piece of metal covering the space of two of the channels on the stereo jack. Have you checked that the jack has a mono plug and stereo socket, rather than the other way round?
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As NReilingh commented above, my pedal actually has stereo output (so the music transmitted from Mac is perfect stereo, not mono in both channels). So it has stereo out and via stereo adapter sound transmitted to sound device. Now the question is, why only one stereo headphones playing only one channel only from the pedal, but not from all other devices. It has metal jack, maybe this can be a cause. Don't know what to think. But those cheap headphones worked with this (this, not the same) jack normally. –  efpies Aug 5 '13 at 15:56
    
I think you need to detail what it is you have connected and how they are connected, then - do you have 1), 2) and 3) attached at the same time? –  Rory Alsop Aug 5 '13 at 15:57
    
No, I have only one output device connected to the pedal. The pedal is connected to the Mac via USB, one of the output devices is connected to the pedal. –  efpies Aug 5 '13 at 16:00
1  
So, if I understand you right, options 2 and 3 are the same, and 3 doesn't work = so it is faulty. –  Rory Alsop Aug 5 '13 at 16:07

The problem is related to headphones cabling. Some have 4 wires (2 for each channel) kept apart from each other, from headphones to the jack socket, while cheaper ones (but not always) have a Y splitter in the middle where the 4 wires become 3 (both ground (-) cables coming from left and right shells are joined together). Depending on relative impedances, this can lead to severe crosstalk when adapters are used. Some extension cables work the same.

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