I'm listening to my Senn HD-580's through an Onkyo TX-8211 receivers headphone out (using a sony 300 disc changer-I also have a project turntable hooked up) I hear an audible hiss in the background, mostly when switching songs (but always present) and it occurs on low and high volumes. Will it help to run a cmoy through this setup or should I cable it a different way?
First thing you should do is probably rotate your RCA cables 180 degrees or try different ICs altogether. The usual test is to short out the inputs and see if there is still hiss (or hum). Is the hiss there if you have no inputs connected (CDP, Turntable, VDP, DVD, Tuner, Tape Deck)? It may also help if you make sure that it is not near a computer and all fluorescent lights are turned off. Also try another AC outlet in a different part of the house. If this were a soundcard, hiss would indicate that there is not enough power to drive the headphone. This may be the case with your receiver.