How sensitive are (let’s say toroidal) transformers for external disturbances affecting the precise uniformity of their field?
Does it matter so much what’s happening at the fringes of the effective field, seeing that the intended function of a transformer is happening in its very near proximity?
If I lined the casing of my amplifier with mu-metal, could it be detrimental to the performance of the dual 650VA transformers? How much do these things need to “breathe”?
(In my situation they’re “breathing” enough to induce audible mains hum to the output through induction via the phono preamp’s ground wire. Made me realize that even phono ground wire should be well shielded)