Hi all. I picked up an HD300 used for a headphone jamming session at a friends home. Playing with it at home before taking it there, everything seems to work fine, except that master volume knob doesn't really seem to control volume. I have the headphones plugged into the pod phone jack. Havent tried thru an amp. I can use channel/master on the amp models to set levels, but I assumed that master knob would adjust the whole thing in the phones. Spinning it either way changes little. MAYBE at low channel volume I can hear a *slight* difference between wide and closed, but I assumed I could kill the phones output by cranking that knob down. Am I doing something wrong?