Someone on Ebay is offering "5-24V REGULATED POWER SUPPLY ELECTRONIC KITs". It's a buy-it-now price of $22.50 plus shipping ($8.84 for me on East Coast.) Would such power supplies be a good thing to use with a Porta Corda II or a Zmoy non-portable amp...

I've got HD580s and I'm wondering what a fair price would be for an Earmax head amp. The unit is in very good condition with 110 voltage input. Also, would this amp be a good match for driving my 580s with a bit of volume? I need lots of volume if I'm using an MP3 player as source. I had...