SUT vs. Phono preamp

I use a SUT for my Denon DL-103 carts. I based my decision on popular opinion plus the fact that it is a passive device. A well built SUT should be dead quiet as there is only a transformer used to boost the voltage. You may have to try different grounding schemes to get all of the noise out but it isn't generating any, it's being picked up from external sources.
An active MC preamp can have noise as it's dealing with so low a signal and must amplify it to a great extent. That is one reason there are so few good tube MC preamps, it's harder to keep them quiet.A lot of folks think that the SUT just sounds better as well if it's properly matched. I didn't buy an active stage after all my research, I went straight to a SUT, actually got it in a trade with another audio friend before I picked up my first MC cartridge. It's a Denon AU-320, perfect match for the DL-103.What cart do you have?
BillWojo

Apart from the SUT or high gain Phono Stage there is a third option such as Headamp (or Pre-preamp).

SUT is passive
Headamp (or Pre-Preamp) is active device

If your MC phono stage can’t handle your LOMC cartridge or you’re not satisfied with the quality, you can use SUT or Headamp and MM phono stage.

You have to pay more attention to the amplification device if your phono cartridge output is less than 0.25 mV, if it’s higher then you may never need a SUT or Headamp and most of the MC phono stages have enough gain to handle your LOMC cartridge.

Still you may like different flavor of the SUT (or headamp) in comparison to the high gain MC phono stage.

As you know each phono stage is different, even of there is a gain for LOMC it does’n mean it’s better than another phono stage + SUT.

"Current-injection" MC phono stage for low impedance MC is something special, it can be much more impressive than conventional MC phono stage.

Noise is not the issue when you're using quality devices, no matter what type.
 
Normally with a Phono Stage you have optional loading for your MC cartridge and you can change it right on the phono stage. To do that with SUT you will have to change SUTs

if you really want to understand SUT’s, here is a reference for how they work and how to choose one.

http://www.intactaudio.com/forum/viewtopic.php?t=752

personally i have 2 SUT’s right now (one with copper windings and one with silver windings) in my system i’m demo’ing. these guys.

http://myemia.com/SUT.html

the advantage of an SUT 'in theory' is lower noise, and 'in theory' greater micro-dynamics, than a head amp since the SUT is passive. in essence; a head amp involves an additional amplification stage which 'in theory' always will add some noise......and reduce the sense of naturalness and ease. as always; there are no absolutes; these concepts depend on degrees of execution. SUT’s are not always better, and head amps are not always worse.

it depends.....

I have 5  LOMCS, one phono preamp and one SUT. Actually, I do not notice much difference between  the phono preamp and the SUT, but I just wanted to know a little more about the theory behind all this; your responses so far  have helped  greatly.