my statement would draw fire when I typed it. That is not the point and I admit that some rare MM/MI cartridges are specified
at something other than 47k ohms resistive.
But getting to the heart of my point, a resistor can be changed with the greatest of ease by a kit builder. And, too, a load capacitor can be added just as easily.
Yet, only a few MM/MI cartridges show an "optimal" load other than 47k. Most affordable, to me
, cartridges say 47k just like when I sold audio gear in the 60s and 70s. I even own a HO-MC cartridge that is spec'd at 47k ohms. Just like the AT you mention. I agree some like it with a different load.
The point, that was confused, is that a LO-MC requires much more matching than a MM. I stand by that statement. See PJ's post below on matching a SUT with a MC cartridge.
The background is that the output and impedance needs to be matched to the gain and transformer impedance. There is no "one size fits all" like panty hose (doesn't work there either, ask your wife). This is from Paul Joppa:http://www.bottlehead.com/smf/index.php/topic,116.0.html