Wow, that is really bizarre, I never encountered that before. Whenever I plug the iPod in it seems to work fine and I can pan both ways hearing everything.
I am going to test this out again tomorrow, trying the XLR adaptor and putting a 1000 hz signal in like you did.I will also try using 2 separate channels.
Thanks for the info, very insightful !
It's likely you have the type that sums left and right properly then. The reason why you get cancellation when identical signals are fed to the hot and cold pins is the exact reason why balanced connections reject noise over long wires - any noise signal common on
both hot and cold lines cancels out when it hits the preamp. Any signal that's in
opposite polarity on hot and cold or only on one of the two legs gets passed. The cold signal in the preamp get's it's polarity inverted and then that signal is added to the hot. Inverting polarity on the cold line is what cancels out any "common mode" noise riding on the hot and cold line. The specs you see for balance connection noise cancellation capability is referred to as CMRR or "common mode rejection ratio." It's a pretty cool concept and has been around since the invention of telephone lines. The amount of cancellation depends on how well the impedance is matched on the source side between hot and cold as well as the receiver/preamp side. The more uneven the match, the worse the CMRR will be and the more common mode noise will get through.