I'm new to Step Up Transformers

Most tube-based phonostages either have built in step up transformers or expect the buyer to use his own step up transformer to supply enough gain.  The typical tube-based phono stage would need to add more tubes and would run the risk of excessive noise if they tried to supply the needed extra gain without using a step up transformer.

The extra gain needed for low output moving coil cartridges can more easily be supplied by solid state phonostages so they rarely include one in their design.  

Aesthetix offers all-tube high gain phono stages which I like, but, they have more noise than most tube stages employing only tubes for active amplification.  Among my favorite tube phonostages are those made by Audio Note which require an additional step up transformer, Zanden (built in transformer), and Viva (built in transformer).  

The Zesto employs a step up transformer for its MC input.  If you go with a separate step up transformer into the MM input, you will be substituting step up transformers.  Whether you will like an alternative step up transformer is dependent on the quality of the alternative, compatibility with the phono stages, compatibility with your cartridge, and personal preference.

The cost of any alternative step up transformer would also have to factor in the cost of another pair of interconnects.  Some of the better standalone devices can be quite high.  The right choice depends primarily with your chosen cartridge, and some companies even wind them specifically for your cartridge.  If you go that route, you might want to learn a lot more about matching.

The Zesto employs a step up transformer for its MC input.  If you go with a separate step up transformer into the MM input, you will be substituting step up transformers.  Whether you will like an alternative step up transformer is dependent on the quality of the alternative, compatibility with the phono stages, compatibility with your cartridge, and personal preference.

The cost of any alternative step up transformer would also have to factor in the cost of another pair of interconnects.  Some of the better standalone devices can be quite high.  The right choice depends primarily with your chosen cartridge, and some companies even wind them specifically for your cartridge.  If you go that route, you might want to learn a lot more about matching.

The Zesto employs a step up transformer for its MC input.  If you go with a separate step up transformer into the MM input, you will be substituting step up transformers.  Whether you will like an alternative step up transformer is dependent on the quality of the alternative, compatibility with the phono stages, compatibility with your cartridge, and personal preference.

The cost of any alternative step up transformer would also have to factor in the cost of another pair of interconnects.  Some of the better standalone devices can be quite high.  The right choice depends primarily with your chosen cartridge, and some companies even wind them specifically for your cartridge.  If you go that route, you might want to learn a lot more about matching.

It is moving iron, but it has a .4 Mv output.  

The approach of using a hybrid transistor and tube to supply the needed gain for low output cartridges is to reduce the level of noise from using tubes exclusively.   

The use of a SUT also reduces noise as an issue and adds the sonic signature of a transformer.  If you want tube only amplification (no transistor stage or no SUT) you have far few alternatives.  I mentioned Aesthetix earlier as an all-tube design that sounds good (if a bit noisy); another good sounding example is made by Lector (quiet for an all-tube design).

lewn,

I agree with you.  The higher the number the LOWER the loading.  At low value of resistors (meaning a lot of loading) small numerical changes do matter a lot (like 30 ohms and 50 ohms are quite different), but, once one gets above 150 ohms, there already isn't much loading and it should not matter that much.  The only thing that does matter is where RFI is interfering and overloading the phonostage.  In that case, a small amount of loading may be needed to cure that problem and this should not affect the overall sound.  A friend suffered RFI that we traced to the default setting on his phonostage being 100kohms (essentially no loading); when we went with 1kohm loading, the problem went away.

On many cartridges, I prefer a lower level of loading (high value resistor)  than most people choose for their setup.  This delivers a wide open sound.  Jonathan Carr, the designer of Lyra cartridges said that modern MC cartridges do not need additional loading to tame high frequency resonant peaks because those peaks are primarily in the ultrasonic range.  When loading does improve the sound, it is because those ultrasonic peaks can overload phonostages that don't have enough margins for peak levels.  I don't have that issue myself, probably because my phono stage is a tube unit that doesn't have extended ultrasonic frequency response.