I've been wondering about the significance of the iPod working hum-free in contrast to the turntables. I switch the input from iPod to turntable on the preamp and switch the input on the amp from AUX to mag phono, and the hum returns with a vengeance (that said, the album sounds good when the hum is overcome). Is this an expected outcome - with the digital source not triggering the hum problem? The amp works silently (as far as background noise) and quite well with the iPod source. I just don't know enough about this stuff to decipher this pattern. I would think that if the preamp were truly defective it should fail with the iPod too??