Audio Systems: Loud hum with preamp and power amp connected, power amp, power circuits

Question
Thanks for your time!
Recently I bought a power amp (ADCOM 555-II) to use with preamp (Classe SSP-30).  But I hear a loud hum from both speakers with preamp and amp connected and I cannot use the power amp.  I have used preamp and it is just ok and the power amp looks ok itself.  I checked the cable and it looks ok too.  How can I fix this problem (loud hum) to use my preamp and power amp together?   I appreciate you for your time and great information.

Answer
Hi!  Sorry to take so long to get back to you, I wanted to make sure I left you a clear and thoughtful response.

 The classic root of this problem is either poor gain structure, signal induction along the "hook-up" cables, or poor grounding ("earthing pin" depending on what part of the world you live in).

Here's some earlier answers about gain structure and hum:
http://experts.about.com/q/Audio-Systems-835/adjust-gain-control-power.htm
http://experts.about.com/q/Audio-Systems-835/Advice-suitable-speakers-amplifier-...
The gist is this though - you should never have your "gain" knob on your amp cranked all the way up if your pre-amp knob is anything less than 3/4 of the way up.

Noise induction usually occurs over long runs of audio "hook-up" cable, usually "RCA's" in the consumer/home audio world.  This is especially true if the cables are near any AC power connections or amplified speaker wire.
Separate your speaker wire from your audio "hook-up" cable from you AC power cables by at least two feet.  Where they have to cross they should do so perpendicular to one-another (90-degrees).

If that doesn't help, get back to me and we can troubleshoot your power grounding scheme.  Some "red flags" to keep an eye out for would be if any piece of audio gear is missing the third "ground pin" on the power plug -especially the preamp and amplifiers.   Also keep an eye out for things powered off separate power circuits (e.g. plugged into different wall outlets or in different rooms).

Here are a few more links to turn you into an expert:
http://www.crutchfieldadvisor.com/S-3W5p58YDSdx/learningcenter/car/noise_diagnos...
http://www.psaudio.com/articles/hum.asp
http://www.audioholics.com/techtips/audioprinciples/interconnects/connectiontips...
http://www.audioholics.com/techtips/setup/avhardware/groundloopcableTV.php
And the ensuing readership angst:
http://forums.audioholics.com/forums/showthread.php?t=5667