When is it time to consider adding a SUT?

The ARC Reference Phono 3, like the Reference Phono 2, has a FET front end instead of a SUT. Mine has plenty of gain to run a Benz LPS into an Aesthetix Calypso.

The LPS is not really a great candidate for an SUT because of its 38-ohm internal resistance (DCR). At .36 mV, you’d likely want to use a 1:15 SUT, which would present an impedance of 209 ohms to the cartridge. That’s pretty low, when you think rule of thumb is 10-25 x DCR (I prefer 25x usually). 1:10 would create a better impedance match at 470 ohms but the gain might be sub-optimal.

I have an older Ebony L at .26 mV and DCR of 3.5 and I use an SUT of 1:20. It sounds good but the loading is a touch high at 118 to the cartridge, accentuating the top a bit. The newer Ebony L has a DCR of 5, which is better for 1:20.

The only Benz that is a truly great match for an SUT is the Ebony TR, which is designed for use with one. With a DCR of 1 ohm and output of 0.1 mV, it should be pretty ideal for an SUT of 1:40.

Thank you for your insight. It is very valuable. My question was not so much about there being enough gain but would the addition of a SUT improve the end to end performance of my set-up and wrm57 indicates that it wont.

I'll report back when it arrives to comment on the end to end performance.   

don't sully yr ref2 with a sut !
it should have more than enough gain for the benz.
keeping the signal path simple will give you the best sound.
;)

I agree with audio_d.  Why add a component, along with ICs and connectors, in the signal path of a cartridge with a very low output voltage, when that is completely unnecessary?  But should you insist upon doing it, you would run the output from the SUT into the MM or low phono gain inputs of your ARC phono stage, assuming it has provision for high output cartridges.  In other words, if you use a SUT, you treat the LOMC cartridge as if it was an HOMM type.  Thus, you would bypass the FET gain stage that others have mentioned.  Not only do you not need to use a SUT, but also if you do insert a SUT, then you need to concern yourself with the quality of the SUT itself, a whole new can of worms.  Not all SUTs sound alike, let alone "good".  Furthermore, the high-ish internal resistance of the Benz is another good reason not to do this, or at least not to assume you will like what you hear.  Highs will likely be rolled off due to the impedance mismatch, which is not a coloration you want to impose on a Benz.