I took some time to A/B my system with Sage in tube and passive mode, now that the Modi 3 is in my system.
I'm using the 6SN7 Tung-Sol New Production Tube that Schiit sells. My amp is Vidar and my speakers are KEF LS50s. I also have a pair of Tekton Pendragon subwoofers which I sometimes turn off depending on the genre of music.
First off, there isn't a huge difference between the two modes, which I think says something good about the transparency of Saga's active stage. The immediate difference is that there is definitely some gain with the active stage on. The difference, to my ears, is about one step on Saga's volume control. I did not confirm this with an SPL meter. For my listening, I switched between the modes and added or reduced the volume that step at the same time to make it an even match.
In terms of the sound quality, while the difference wan't large, it was easily noticeable. I'm fairly certain I'd be able to pick out one mode over the other in an ABX test.
The difference, as best I can describe it, is that in tube mode, there was something "more" to the sound. I don't mean that in necessarily a positive way. However, after spending some time with music that I like, I found myself preferring the sound with the tube engaged. I felt that whatever sound was being added to the music had a very pleasant harmonic effect.
I also got the sense that the passive mode was more accurate. Listening to live studio recordings, the separation of instruments and vocals was more clear and it was easier to pinpoint a location in the soundstage for each. Another way to put it is that the space between the instruments was more empty, or black. On a handful of songs, this improved the realism of the sound. It provided a better "artist is in the room with you" feeling. The album that I felt this most strongly with, and the only one I found myself outright preferring passive mode on, song after song, was "Love Has Come for You" by Steve Martin Edie Brickell.
However, in most other recordings, possibly due to lower production quality, the songs didn't sound more real in passive mode, just a little more flat. The tube section often made the sound feel more cohesive in a positive way. Another way I can explain it is that in tube mode, the whole soundstage in front of my was filled, whereas in passive mode, there were "holes" in the sound. Now, if those "holes" are supposed to be there and help improve instrument separation and such, that's good. But I listen mostly to modern music which, the vast majority of the time, isn't produced well and doesn't have clear instrument separation to begin with. With those recordings, passive mode didn't make the music feel more real, and most importantly, it lessened the emotional impact of what I was listening too. Even on some well recorded music, where my preference was more of a toss up rather than an outright preference, I tended to lean towards the tube mode for this reason.
Like I said at the beginning, these differences were mostly subtle, but I could hear the same effect on a number of different songs in different genres, so I'm fairly confident in what I was perceiving. Of course we all have different ears so you might hear something entirely different than me.
My main takeaway is that I will continue to use the tube stage in most of my music listening, but now I'll definitely try the passive mode as well when listening to acoustic, live, or well produced recordings, or when I'm in a more critical mood. However, for me, listening to music is more often an emotional experience, and the tube mode improved the impact, less accurate or not.
I also got my LISST in the mail a few days ago. Once I get it in my system and let it burn in for a bit (just to be sure), I'll do another comparison and see if any of this changes.
I have been around electronics for a while but I thought Grade A applied to eggs, who could have imagined tubes were graded that way as well?
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