Tones,

Sloppy language on my part!

The steel though definitely could become permanently magnetised, the nickel, less so, although I guess this may also be more related to the switch-on DC changes rather than the run-of-the-mill AC music signals.

There is no doubt though that ferromagnetic components in the signal path increase distortion, measurably, when compared to non-ferromagnetic ones (which also usually sound better, all else being equal).

Andy.