Perhaps there may be directionality?? I am not getting hum on my amp which has integrated dual bobbin type. Please refer to the pictures at:http://www.head-fi.org/forums/showth...&threadid=3403
You should notice that the transformer iron layers are perpendicularly to the amplifier board. PSU module is positioned parallel to the iron layers.
I know that shielding magnetic field is virtually impossible. What I know is that it will not propagate over distance. So all we can do is to keep trannies away from amps.
(Faraday Cage do not work as Magnetic field shield. Non-Zero charge concentration at the conductor boundary surface does not damp magnetic interference. However, it is true that electric field will be completely shielded by Faraday Cage.)
Perhaps it may have something to do with the ranges of interference. I know that E field str is much larger than M field str. So the range of M field will be smaller than E field range. (i.e. The distance at which field is no longer significant)
From my recent experience with tranny, it seems the distance from tranny does not need to be really large. For my amp, the distance is less than 10 cm. (CENTI-METER) Whata heck is going on here? It did not show up on my calculation!!
P.S. Leonids beautifully decorated the winter sky with trails of light much like fireworks. I saw like 50 meteors this morning. It was exstatic experience; I have never ever seen meteor showers. Only thing missing was higher temperature; I got frozen ... Soooo sooo cold here!!