This happens because the GND is shared in the headphone for each channel and where a mono jack that has a plastic shell and instead of connecting with the shell, uses a connection that normally is where the ring is on a stereo plug. The jack connects to the ring of the headphones (expecting to connect to the shaft of the mono plug) and you get what appears to be a mono signal but is in fact both left and right being connected serially (through the shared ground). The ground being connected together and the ring connecting to the true ground. Positive jack to left positive, left negative (shared GND) to right negative (shared GND) to right positive to mono jack GND (instead of ring). This happens on headphones because they share the single ground for both left and right.
-James

On Jan 9, 2012, at 4:06 AM, yahoo@... wrote:

>> Dear group,
>>
>> Just like Bakis I want to wish you all a good 2012!
>>
>> But now, something completely different.
>>
>> When plugging in headphones in an audio out connector (VCA,
>> mixer) I hear both the left and right channel.
>> However, if I route the audio out through a multiples, the audio
>> signal is halved, only the left channel is left.
>> Is this caused by a difference in the audio out and multiples connectors
>> Hope someone can tell.
>>
>> Warm regards,
>>
>> Ton
>
> Also from me Best Wishes for the New Year!
>
> The mechanical construction of monophonic 3.5 mm jacks and plugs is
> different from stereophonic versions. Parts of the long GND sector of the
> monophonic versions is used in the stereophonic versions as the second
> signal. It depends upon the mechanical tolerances and the plug-in depth what
> happens if a stereophonic plug is connected to a monophonic socket.
> Typically the second stereo signal will be dead as the corresponding sector
> of the plug is not connected or connected to GND (depends upon the
> mechanical details of the monophonic jack socket). But there might be an
> intermediate plug-in position where the monophonic signal appears on both
> stereo channels.
>
> As there exists no technical specification that describes what happens if a
> 3.5 mm stereo plug is connected to a monophonic 3.5 mm socket you will have
> to try it out. In the A-100 two different 3.5 mm sockets are used (vertical
> and horizontal) and maybe they behave different.
>
> Best wishes
> Dieter Doepfer
>
>
>
>
>
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