Will Step Up Transformer Improve the Sound Quality?

To build in SUT inside isn't the good one idea. It will catch more noise so SN ratio will be inferior compared with external one. Friend of mine builds tube phono stages so customers usually wants SUT inside as it makes less space and less wiring for it. Although the same external SUT performs better.
Mostly for SUT he uses Lundahl various types. And they are really good ones but nothing spectacular. But from the price point Lundahl is the best, IMO. If to hear spectacular you have to look for artisan designs some of them are really good ones. Then you'll find your favorite you'll forget active gain stages, head amps etc.

More noise? Less noise if you shield carefully and keep AC far away. Or so it seems to me.

Of course if you put an SUT near a high voltage power supply you are asking for trouble.

I have various SUTs, special Headamps, High Gaing MC phono stages (with adjustable gain), MC phono stage with built-in SUT is the quietest of them all ... 

What is really special is Current-Injection type of MC phono which I also have (for low impedance MC).

I like simplicity, less wires, I would like to use just one box instead of two. 
But if you like different flavors you must try what you like in your system! Don’t ask others what you will like. 
If you want to try a SUT there are so many top quality SUTs from the Japanese manufacturers, inexpensive classics from the 70’s, 80’s. 
If your cart is low impedance try Current-Injection type of the MC phono stage instead of the SUTs

I have various SUTs, special Headamps, High Gaing MC phono stages (with adjustable gain), MC phono stage with built-in SUT is the quietest of them all ... 

What is really special is Current-Injection type of MC phono which I also have (for low impedance MC).

I like simplicity, less wires, I would like to use just one box instead of two. 
But if you like different flavors you must try what you like in your system! Don’t ask others what you will like. 
If you want to try a SUT there are so many top quality SUTs from the Japanese manufacturers, inexpensive classics from the 70’s, 80’s. 
If your cart is low impedance, try Current-Injection type of the MC phono stage instead of a SUTs

@chakster 

We ask for opinions of people who have experience with different options (in this case SUTs vs electronic gain) in order to gauge if there is a good reason to try them.  
That is what this forum is about !