SUT vs. Phono preamp


On what basis is  the decision to chose  a SUT vs. a phonostage made?
boofer
My phono stage is a Rega Aria, not exactly top of the line, but at $1500, no slouch either.

Ok, this is your phono stage

70 Ohm, 100 Ohm, 150 Ohm, 400 Ohm

63.5 db and 69.3 db



There are dip switch settings for all Rega MC cartridge models, but what about your MC cartridges, they are all Rega ?







A SUT can ring etc. so is not without possible sonic artifact. On the other hand a SUT more or less can't pass rfi which may bring a benefit to your phono considering the MC ultra high hf bump...so like most things audio comes down to specific implementation and pairing.
None are Rega; They are Benz Micro Gold, AT 33ev, AT F2, and your favorite Denon103D.  Haven't  tried it yet.  I usually use the vintage MMs, but recently wanted to play MCs against each other, which the Aria lets me do easily. MM's: At 12sa, at 440ml, shure v153 and M92e, Micro acoustcs 2002e,, Stanton 881s, and Empire 2000z, also  Goldring 1042, and many more.l The Stanton and Empire come in as  champions for overall performance..
''additional amplification stage...will add some noise" (mikelavigne).
I use a SUT for carts with less than 0,2 mV output. However I
will start  not with ''theory'' but with practice. I own two phono-
pres both with 4 amplification stages. Basis Exclusive and Klyne
7PX 3.5 . Both recommend the use of the lowest amplification
stage in relationship to carts output. The ''theoretical'' assumption 
being ''the bigger amplification the bigger distortion''. I also own 
Denon AU-S1 SUT but use only with my Ortofon MC 2000 with
0.0 5 mV output. For outputs above 0.2 mV I don't need an SUT.