With electro grade copper skin depth is 8mm at 50Hz. Put whatever you want to shield in a container (faraday cage) made out of thick enough conducting material (the better it conducts the thinner it can be) in a way it provides a "short" in all directions (like a real faraday cage does) and it will certainly provide shielding also at audio frequencies.
I shielded my 50Hz induction heater experiments that way, and it worked good enough to prevent health issues (before that I was very worried because I could feel the stray field in my eyes and also hear all kind of noises made by screws, tin cans a.s.o. meters away, even the iron in the beton ceiling above my head made worrying noises)
Off course a "plate" just put between two coils will not shield the way a faradays cages "short circuit" does
I shielded my 50Hz induction heater experiments that way, and it worked good enough to prevent health issues (before that I was very worried because I could feel the stray field in my eyes and also hear all kind of noises made by screws, tin cans a.s.o. meters away, even the iron in the beton ceiling above my head made worrying noises)
Off course a "plate" just put between two coils will not shield the way a faradays cages "short circuit" does
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To shield a length of wire or cable from magnetic interference the shield must be connected to GND at both ends. Magnetic coupling can be modelled using coupled windings. If you float one end of the shield it is as if one of the windings is floating on one end - does not do much does it...it might as well not be there. As a matter of fact it may resonate and make things worse (at high freq). Short circuit both ends together and we see the coupled windings all get shorted and signal (noise) is shorted out. Shield braids in cables are seldom of ferrous metals yet they shield magnetic fields as long as both ends are connected.
Is anybody on this thread actually having a problem with hum, that is caused by magnetic fields that are coupling to a sensitive part?
Fortunately, most of my amplifiers have less than 100uV of hum with an 8 Ohm resistive load.
And, even with the output tap open, the hum is still at a very low level.
Of course that is too high for most headphones, but I do not use headphones.
Fortunately, most of my amplifiers have less than 100uV of hum with an 8 Ohm resistive load.
And, even with the output tap open, the hum is still at a very low level.
Of course that is too high for most headphones, but I do not use headphones.
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