You have inspired me to finally pull the trigger on a new SUT for my Koetsu - have been Hamlet-ing the decision for almost a year and a half now. So thank you. I went with the Swissonor, will report back.
Re SUT vs. active stage, I had a great discussion (email) with Andrew Rothwell before I bought one of his units several years ago. Here’s a portion of his thoughts:
“Hi Steve. Yes, noise is indeed a potential problem with headamps - but noise is a potential problem with any audio electronics. Actually, there are various types of noise and various ways it can infest an audio signal. The type of noise most likely to plague a headamp is Johnson noise, aka thermal noise, which is a hissing sound. With a step-up transformer you're unlikely to have any hiss problems, but you're more likely to have hum problems. Anyway, without getting too deep into the topic of noise, let me assure you the Headspace has very low noise - way below vinyl surface noise. I leave the choice between headamp and SUT to the customer, but with your system being valve-based the transformer option seems more fitting - no transistors :-). Btw, no the battery doesn't address the issue of Johnson noise at all. It addresses the issue of mains-borne noise and potential ground loops. Regards. Andrew”