My best option was placing three, on the back side of my
amp's transformer. The magnets don't "stick," as much as they
just stay in place. They are from Monster Magnets,
www.magnetsource.com
They are circular, with a hole, measuring .74 in od x .375 in id
x .105 in thk. These were the biggest ones in stock at a
local electronics store, $15.99 for three.
In my opinion, equal to or better than a cable or power cord upgrade!