SUT - electrical theory and practical experience

Enough Raul.

Thought I share my perspective. In short, SUT’s are imo very cost effective and it easily gets forgotten. Some people have restrictions, for example room/placement and/or economical limits. Thats the case for me. 
Have Kenwood KD-990 (increased mass on tonearm) with Denon DL-103 for the past 25 years. Monitor audio speakers just as long. Standard gear all the way. 
Phono preamps have changed over the years though and also nowdays have a Denon DL-305. Started with cheapest Pro-ject stage and my last and to me most ”expensive” phono preamp was ASR Mini Basis. It was a nice sounding unit for sure, but there was constant noise from the speakers. Not too bad and didnt really notice it once the needle dropped but there was noise for sure. Decided to try a SUT instead, bought AU-340 and never looked back. I run the SUT to my Denon AVC-X8500 built in phono stage (I assume its crap!) still this is the best sound I had. Paid 350 USD for the AU-340, there is absolutely no way a phono preamp at that price would stand even the slightest chance against the SUT. So take this into consideration please. Also, maybe some people like fiddling around with dip switches and experimenting with loads etc etc, I did with my ASR but the whole thing just annoyed me at the end. 
I am about to buy a better MM phono preamp now. No silly money though, looking for something tops 500 USD. Any recomendations apreciated. 
Respect and thanks for a great forum that helped me a lot over the years.

rubandscrub - the cost effectivity is certainly an important aspect, like you write. I also have an ASR Mini Basis, now used mainly as a backup in case my main phono stage has problems. If your Denon carts have 0.2 - 0.3 mV output, I am not surprised that things improved with a SUT. More 'muscle', I imagine. Although I think the sound of the Mini Basis is quite good for the price, it is a bit 'polite', even with my 0.56 mV cartridge. The noise you heard may be due to stretching it, with the gain at or near max (I did not have this problem, using a medium setting).

Hi, I am looking for some real world advice. I recently purchased a new LOMC (Etsuro Urushi Cobalt Blue) that has an output of 0.25mv and 3 ohm internal impedance. I use an Allnic H-3000 phono preamp. An audio friend has the next step up (pun intended) of my cartridge with similar specs. Not sure what phono pre he uses. He swears by the SUT he’s using with it (Luna Cables Rouge):

My question is:

With the Allnic’s design, is it likely that I would achieve a significant improvement in sound quality if I were to add the right SUT (the Rouge may or may not be “right” for my cartridge specs)? I must say, the cartridge sounds great with the Allnic but only compared to the last cartridge I was using, a Kiseki Purple Heart, but maybe there’s a chance I’ve left something on the table?

The H 3000 already uses built in step up transformers for moving coil cartridge levels of gain. If you want to use an external step up transformer, you would need to use moving magnet cartridge inputs on the H 3000. I don’t know whether the H 3000 even has MM inputs. If it does, that’s where you could go. You cannot hook up an external step up transformer to an internal step up transformer. Personally, I think you may be chasing your tail if you are even able to try this experiment with your H 3000, because the internal step up transformers on the H 3000 are already excellent.