I have a Harman/Kardon 1650 and it came with a 1/4-inch stereo plug converter. However, when I plug in my headphones (I tried about 4 different ones), I only get audio through the left side and nothing at all on the right side. I checked the manual and there are no special instructions. I don't know if there is something wrong with my receiver or if my setup is wonky. I currently have the receiver hooked up to my computer via HDMI. Everything is working fine except for this one thing. Any help?