I'm almost a week in with the ndh 30 and what really stands out to me about them more than anything is how engaging they are. i generally dislike very neutral sound signatures, as they come across as boring to me. but these are anything but boring. they have excellent dynamic range, and excellent impact. they're honest in that they don't add any omnipresent coloration (like my beloved Atticus does), but when bass is called for they deliver. i was listening to Rush's YYZ, which is a bit lean sounding of a recording IMO, and after that Andrew Combs' Anna Please came on, with a really strong opening bass beat. the bass on Anna Please made me flinch, after being acclimated to the leanness of YYZ. that led to many hours of me searching my playlists for the best dynamic recordings i have to experience them on the 30. if there's any complaints so far it would be lower treble, where a lot of female vocals rest. i'm treble sensitive and the 30 has excellent presence there. its not sibilant or strident, just maybe a bit too much presence for my tastes. grain of salt though as i like rolled off treble in general, so very much a preference thing.
I did test the 30 for a few hours on my Jot 2 to gauge it without tube amp coloration. it was a tighter, more responsive listen vs tubes, but also a touch leaner, which I did not like. bass impact was hard and forceful, but lacked the more natural decay and linger tubes provide. upper mids and treble were also a touch cooler sounding, though thankfully still not sibilant or strident. soundstage was a bit more intimate on the Jot 2 as well, though that's a fate all solid state amps share when compared to a good tube amp. overall it was a more technical presentation, but lacking a bit of the engagement factor i find so irresistible on tubes. but the tonal difference wasn't that that big. if i had to sell my tube gear i could live with the Jot 2 and still be happy.
another thing i'm finding with the 30 is it's very sensitive to output impedance, much like the 300ohm Sennheiser models. all my solid state gear runs ultra low output impedance (less than 1), giving a very high dampening factor. but my tube gear varies significantly in regards to their output impedance. my Stratus runs 8ohm and 120ohm (or maybe 150, i forget), whereas my Kenzie OG2 runs 32ohm and 300ohm. finally my MicroMZ2 runs 2ohm. the 30 changes noticeably on all of those amps, and oddly at times as well. what i mean is sometimes what "should" be underdampening actually sounds excellent, with no performance trade offs. for example the 120ohm output impedance option on my Stratus matches the impedance of the 30 exactly, resulting in a 1:1 dampening factor. normally a general rule of thumb is keep your dampening factor at 1:8 or 1:10. anything closer to 1:1 results in underdampening, which normally degrades the sound quality. underdampened headphones tend to sound slow, bloated, brittle, and distorted. but the 30 and Stratus running a 1:1 dampening factor sounds tight, forceful, and dynamic. i get no hint of underdampening at all, and so far feel the 30 sounds best there of all my amps. Zach of Ampsandsound did tell me once dampening factor rules sometimes go out the window when running transformer coupled tube amps. something about the transformers that affect dampening factor. i believe that might be the case here, as Donald uses a very high quality transformer in the Stratus. but IMO the 30 just rocks on the Stratus 120ohm output. i love the warmth that combo brings, while not affecting the technical performance.