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When LOMC cartridges appeared at the same time the LOMC manufacturers designed/manufacture too SUT because there was not active high gain phono stages. So, all phono stages came with 47k where the SUT must be connected.
Latter on appeared the active high gain phono stages to drive LOMC in exclusive way with no facilities to handle MM/MI cartridges, even those LOMC phono stages cames ( even some today ) with impedance load different values choices coming from 100 ohms to 1k ( more or less. ) where no one came with the option to choose 47k. "