I recently purchased a new set of QC20 headphones, and have had different issues when trying to use them with my AV receiver. The AV receiver is a Yamaha RX-V385 if that's important.
-If I try using a 3.5mm audio extension cable that has 2 black lines on the connecting end, I get a loud hum when I turn on the headphone power.
-If I try using a 3.5mm audio extension cable that has 3 black lines on the connecting end, the hum is gone, but the volume on the left side is significantly lower.
-If I connect the headphones directly to my AV receiver without an audio extension cable (6.5mm stereo adapter is still required), I still get low volume on the left side.
-When using the headphones with my IPod, both sides have equal volume levels. This was attempted with and without the 3.5mm extension cable that has 3 black lines on the connector end.
My assumption at this point is that the headphones won't work properly with a standard 6.5mm stereo adapter, and that I need a specialized 6.5mm adapter with 3 black lines on the connector end, much like all the other combinations that have worked thus far. I'm hoping you'll be able to give me a workable solution for this problem.