When is it time to consider adding a SUT?

Depending on whether you’re running the cart in balanced or unbalanced, the Ref 2 will give either 74 or 68 dB of gain(respectively), which SHOULD be plenty, with even a very low output cart. Especially given how low the noise level is with the Ref. The Benz LP-S is rated at .36 mV, which isn’t as low as many. Everything will depend on the rest of your system’s gain, speaker efficiency and your preferred SPLs.

You have plenty of gain for the Benz LPS. I use a Benz LPS with my ARC Reference Phono 3 with no gain issues.

Doesn’t the REF 3 already employ an SUT when running through their MC input. I think at times it’s overlooked, but most tube phono stages have built in SUT’s. Manley, Aesthetix, and as all who frequent A-gon know, Atma-Sphere, do not use an SUT. IME, 68 db should drive a .3mv Benz. Not an easy task for a tube stage without an SUT, but 68db should work, pending it's quiet enough for you. I drove a  Benz Ruby 3 with a Lamm LP2, and the 57.5 db gain was not quite enough.... Cheers -Don

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.