[sdiy] Noisy transformers and faraday cages

[Mike]

Toroidal transformers have much lower hum fields than normal E-lam types.
Twisting the AC leads together and keeping them close to the metal chassis
baseplate, (old valve heater liners trick), will help too. Try and keep the
higher current lines away from the signal, they are the ones with the worst
field - secondary side is often worse than mains for magnetic pickup.

A decent toroid may cost less that the mu-metal. One lasrt point NEVER mount
a toroid with a centre bolt and side boolts through a conductive material.
You get a single shorrted turn, which can literally melt. A friend did this
years ago with a home made HiFi amp. He melted the 1/4" alloy base plate of
the case.

Mike