A question about enclosure material for a filter
Non-magnetic metal enclosure dampens substantially 50Hz magn field only if it's several centimeters thick. Dampening happens via eddy currents. Soft iron (or even better high permeability mu-metal) helps if the thickness is one millimeter. High permeability closed case directs the low frequency magnetic field to pass the internal circuitry. Thick iron of course is better than thin. I have succesfully used 4mm iron case around an audio transformer near a power transformer.

You can also keep 50Hz magn field out of the signal by having no loops that generate voltage from it. If you have inductor, split it to 2 identical inductors which have opposite directions => catched sum voltage=0

If 50Hz is out of band, you can kill it by filtering.

A tight metal case is useful against high frequency noises.