I've got a pair of the VPI Magic Bricks also. Placed atop the power transformers of my main amps the result is an instant and profound improvement in overall focus. The Bricks contain a grain oriented iron that perhaps redirects the x-former's flux away from the rest of the electronics, or suppresses eddy currents within the x-former(or both). I'm certain the weight helps dampen vibrations too. Atop the output x-formers there is no difference at all. These were the first "tweaks" of their type that I tried(years back), and was astonished. I wouldn't think of parting with them.
