Amplifier hum - normal?

There's also the Humbuster III from PS Audio. The DIY solution costs much less though.

http://diyparadise.com/dablok.html
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Hmm... DIY you say... how would one go about such a project?

Install the DC blocking circuit in a metal enclosure with a 120V 15A single or duplex receptacle. Insert the blocker between the incoming HOT line and HOT terminal of the receptacle.

Its probably easiest to install everything in a 4" x 2 1/8" or deeper steel electrical junction box and use a cover plate with holes for a single or duplex receptacle. Alternatives are a metal power strip enclosure or aluminum project box.

You can use a 3-wire grounded 14 gauge or 12 gauge power cord for the input and be sure to bond the incoming ground wire to both the metal box and ground terminal of the receptacle. Also use an appropriate strain relief at the point where the cord goes into the box.

The caps and diodes can be obtained from Radio Shack, Parts Express, Mouser, etc. Radio Shack does not seem to have 3,300uf caps but they have 4,700uf 35V which will also work.

See this circuit:
http://img.villagephotos.com/p/2003-5/191557/DC%20Blocking%20Circuit.jpg

Enclosure and two types of 1/2" cable connector/strain relief:
http://img.villagephotos.com/p/2003-5/191557/J_BOX.jpg

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Hmm... I think it's a bit over my head. I've never made a circuit... but, I suppose this may be a good place to start.

Do you have a friend or relative with good basic electrical knowledge to whom you can turn for help ? If you are unsure of your skills, then don't attempt this. Also, the cans of the capacitors are going to be at line potential. They have plastic shrink labeling around them but there is still some bare metal exposed. You need to exercise care that these don't come into contact with anything else. Observe polarity of the caps and diodes. The caps usually have a (-) marking on the side with the negative lead to indicate polarity. The diodes have a band on one side to indicate the cathode (negative) side.