Thank you Stanwal and Tbg, that was informative. The funny thing is that I had Denon POA 2400 (200W/channel) not a sign of hum, but the DK does have a faint hum. I guess I have to live with it as it's not audible 3 inches away from the amp. The Denon had a cheap 2-pront (no earth) power cable, do you think the grounding might be an issue? I had a B&K MC 101 Pre-amp with a IEC power cable and that had a hum too.