Professor:  What does hum 120dB below the peak output mean?  See Fanatics Only for a discussion of dB.
 

Golden Ears:  Perform the hum test yourself. With the amp knobs where you normally listen and everything off except the amp, stick your head as close as possible to the center of the woofer. (Don’t touch it!) With most amps you will hear background hum. The SLC-A300 is completely quiet. Check your other equipment: Preamp - turn it on and repeat the test. CD/DVD - plug directly into the amp inputs. Play something, put it on PAUSE, and then listen for hum, motor noise and background clutter.