Added an SUT...not sure I understood this

@woofhaven1992 

Here is what you need to know -

Your Audiotechnica AT-OC9XML has an internal impedance of 12ohms and voltage output of 0.4mv

Therefore it needs to see a load higher than 100 ohms ( as per specs ).

When you ran the OC9 straight into the SP14 with a 40ohm loading resistor you would have strangled the sound.

Now the AU320 step up.

The 3ohms and 40ohms on the front panel refer to the cartridges internal resistance - NOT the loading.

With the 3ohm input, the gain is 36x which means the cartridge will see a load of 36ohms. The SP14 phono will see 14mv. The sound should be awful because the cartridge at 12ohms cannot drive 36ohms, and the FET based front end of your phono is probably overloading.

With the 40ohm input on the AU320 the gain is 10x which means the cartridge will see a load of 470ohms which is fine, the phono input will see 4mv which is perfect.

Adding loading to transformers can be a minefield, therefore I would suggest you run the AU320 into the SP14 phono at 47k without any additional loading resistors .

What I would suggest is get a pair of 470ohm resistors and try running the OC9 straight into your SP14 loaded at 470ohms. This will give you a direct comparison with and without the step up with the same loading. You might find the SP14 phono with the OC9 at the correct loading may be fine. Of course the additional step uphill add gain if you need it.

A Schiit Mani 2 ($150) with its mc gain setting probably will sound better than the SP14 phono/SUT combination.

Vinylzone, I think you’re correct about the labeling of the SUT inputs, but in this case the best choice is the 40 ohm inputs despite the fact that 12 ohms ( the internal R of the cartridge) is closer to 3 than to 40. That labeling custom can be very misleading. “40 ohms” results in a 1:10 step up, which is what is needed here. The 1:10 voltage step up will give you an input Z of 470 ohms. That would be about 10X the internal R of 40ohms. So the label really only means that pair of inputs is ok for cartridges that have a 40 ohm R or lower than 40 ohms. I am glad that “logic” is no longer used.

The EAR MC-3 and MC-4 also use that "tap / coil ohms" labeling, and I hate it lol. There is no "standard" for what actual dB gain or ratio these ohm labels correspond to. And they generally assume a traditional iron coil former (efficient), but cartridges with the same coil impedance can have wildly different output levels (or vice versa) depending on design - look at Benz’s LPS (ruby plate former) with 38 ohm coils providing 0.34mV output, versus My Sonic Labs with 1.4 ohm coils for 0.5mV output!

This kind of taps labeling works better for tube speaker amps, because almost everyone has either 4 ohm or 8 ohm speakers, and gain matching isn’t as crucial there (adjust your preamp volume accordingly, to an extent).

For a SUT, labeling either the gain ratios OR dBs is much more useful. On my EAR MC-3, the taps: 4 ohms, 12 ohms, 40 ohms correspond to (I think, roughly): 4 ohms = 28x (+29dB), 12 ohms = 18x (+25dB), and 40 ohms = 10x (+20dB).

I think this tap labeling was used only to help its users avoid the most minimal amount of math calculations: match your cartridge's coil spec to the tap, and hope the SUT designer had your cartridge's relative design / efficiency in mind.