I am using the EMI and Columbia cards besides of the RIAA curve. It is worth doing so in case you have the old vinyl!
you see the cards standing in the first row of the phono in front of the image.
A plate made of steel should block possible impact of magnetic fields.
AudioCirc.com 
Did you changed Phono EQ from Allnic H-5000 to Boulder??
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I have both!
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My uncle Bill Durst worked for many years at RCA (1932-1982). He made a phono preamp in the 50 ties with all known compensations, including riaa. When visiting the family in 1968 in Indianapolis he demonstrated the differences. They were profound. He ended up in Japan helping out Japan Victor Company with new technology. He had worked with development of color TV´s in the 1930 ties (and US radars during ww2). He inspired Me in 1968 to get involved in hifi.
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You were so lucky having a uncle-genius like him.
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