52 db is a suboptimal match for your 0.5 mV Shelter, since it place the signal too far down towards the noise floor. By the time you raise your amp volume to compensate, audible hum & noise is the inevitable result. At 52 db it's really too low to call a proper MC input, since that only matches well with the highest output MC's.
On the other hand, 52 db is very high for an MM stage, thus limiting its options for SUTs. So it's a little bit in no-man's land (other than high output MC's). However if the overload margin is good on that MC input, and it can be set to 47K loading, then you might significantly improve sound with e.g. a 1:10 Bob's Devices Sky SUT into your phono stage. I have a 1:20 Sky and Shelter Harmony (also 0.5mV) into a 44db/47K phono stage, with great results. You'd have a total of 72 dB gain with a 1:10, which isn't too bad because now you'd be turning the amp volume DOWN to push down the noise floor (with signal riding MUCH higher above this floor). Also, a Lundhal 1131 or 1141 at 1:8 or 1:16 gives great results with my Shelter. The Sky renders a meatier, fuller sound with great slam, and the Lundahl is more delicate and airy. Pick your poison!
On the other hand, 52 db is very high for an MM stage, thus limiting its options for SUTs. So it's a little bit in no-man's land (other than high output MC's). However if the overload margin is good on that MC input, and it can be set to 47K loading, then you might significantly improve sound with e.g. a 1:10 Bob's Devices Sky SUT into your phono stage. I have a 1:20 Sky and Shelter Harmony (also 0.5mV) into a 44db/47K phono stage, with great results. You'd have a total of 72 dB gain with a 1:10, which isn't too bad because now you'd be turning the amp volume DOWN to push down the noise floor (with signal riding MUCH higher above this floor). Also, a Lundhal 1131 or 1141 at 1:8 or 1:16 gives great results with my Shelter. The Sky renders a meatier, fuller sound with great slam, and the Lundahl is more delicate and airy. Pick your poison!