Hi all ! I was about to start a new thread but diyaudio automatically suggested this one, so here is my problem. For years I've been using shielding in equipment, more as a recipe or as prevention but never knowing much about the details. I know the theory. Now, I need to be sure that a low level magnetic cartridge preamp input stage is properly shielded from EMI, transformers fields, RF, etc. The device I designed is very simple but uses a small, inexpensive plastic case. I would like to use this
copper foil .
I took an old piece of copper strip of about 0.5 mm thickness and placed on one side a powerful piece of magnet (from an old hard disk drive) and a metallic washer on the other. To my surprise (and perhaps because of my ignorance on this subject) the washer was effectively attracted by the magnet and remained stuck to the copper strip. I changed the magnet for a much smaller one with same results !
So my question is: how does copper and aluminum shielding works ? Are there different shielding grades ? If I shield my plastic box from the inside and taking care of electrically connecting all planes by soldering or with cables to signal ground, would I be really shielding my sensitive circuit ?
I would like to hear from the experts. Thank you in advance.