The best answer to your question is another question, viz., "Which MC phono stage are you using?"
As several have pointed out, the optimal impedance for an MC is system dependent. To be more specific, the type of MC gain has the greatest influence. With the exception of John Tracy, every poster so far has assumed an active MC phono stage. John's much lower number is based on using step up transformers, which is very different.
I owned a 901 and the optimal impedance varied considerably depending on which of four SUT's I used. When I switched to an active MC phono stage the optimal impedance changed even more (higher).
Unless you're using the same MC gain stage, no one else's specific number would be applicable to your system. This is especially true with SUT's, which are highly variable, but it's even true with active stages.
So, what are you using?
As several have pointed out, the optimal impedance for an MC is system dependent. To be more specific, the type of MC gain has the greatest influence. With the exception of John Tracy, every poster so far has assumed an active MC phono stage. John's much lower number is based on using step up transformers, which is very different.
I owned a 901 and the optimal impedance varied considerably depending on which of four SUT's I used. When I switched to an active MC phono stage the optimal impedance changed even more (higher).
Unless you're using the same MC gain stage, no one else's specific number would be applicable to your system. This is especially true with SUT's, which are highly variable, but it's even true with active stages.
So, what are you using?