Intro
Having now lived with this amp for a bit of time and played around with different tubes, I think I'm now equipped to write up some more organized impressions of it. I don't have any other amp to compare it to at the moment, but I have fairly clear recollections of my SW51+, ZMF Pendant, Elekit Tu-8800, and 3F and how each of those sounded with Sennheisers. The former two will serve as the main points of comparison. To give a TLDR: I think this amp is a pretty good deal if you can deal with some of its idiosyncrasies. It definitely punches above its price-point: the other stuff I've heard at around the 1k point, like the used Bryston BHA-1, doesn't really compete, and it blows lower priced Schiit stuff like Lyr 3 and Valhalla 2 out of the water, as it should.
But it's certainly not perfect. I'm going to work through each band of the frequency response, dedicate a paragraph to technicalities like dynamics and staging/imaging, and then talk a bit about the overall way that the amp presents sound. Instead of having discrete paragraphs comparing the amp to other ones, I'm going to try to integrate comparisons throughout the entire review.
Chain: Roon via Pi2aes --> Bifrost 2 --> Quicksilver Amp with RCA 12ax7's and Mullard New Production EL84's.
Bass
Probably its weakest point in the FR. Although it extends deeper than something like the SW51+, it doesn't come close to UL designs like the Pendant and Elekit TU-8800. It tends to be fairly punchy, but it also lacks a good deal in texture, nuance, and detail. This was particularly apparent on tracks like Lou Reed's "Charley's Girl", where you can normally hear a very distinct clicking sound with the hit of the drum, but this is obscured on the Quicksilver. I'd say this isn't really a step up in bass texture and quality from something like the SW51+ - where it does do a bit better is in just the bass quantity it provides as well as the bass dynamics that it offers, which are solid but not astounding. Overall, the lack of -clarity- in the bass can lead to a somewhat muddy presentation, but thankfully there isn't too much of it, so it can mostly be ignored by those who are more interested in other elements of music.
Mid-range
The amp's strongest suit. There is a noticeable but not overwhelming amount of bloom in the lower-mids which contributes to a certain amount of tube romance, but upper-mids also feel very much present, giving nice edge and presence to vocals. In fact, the level of "wetness" in the mid-range is complemented by what seems like a slightly up-tilting FR into the upper-midrange, which contributes to a good sense of balance. Compared to the SW51+, the mid-range presentation sounds noticeably more lush and less lean, and images tend to have more flesh and dimensionality to them.
In conjunction with improvements in transient presentation and dynamics in the mid-range, this leads instruments and vocals to "pop" more and simply have more color and vivacity compared to something like the SW51+. The Pendant has a similar effect, but the overall presentation of the mid-range is quite different due to the Pendant's warmth and more hefty bottom end, which leads to a mid-range that has more fundamentals and less harmonics, making it a somewhat more relaxing but also less exciting listen.
The amp's mid-range is let down a bit by its lack of resolution. Although both the SW51+ and the Pendant lack the sense of excitement and engagement that comes from the Quicksilver's combination of bloom and quickness, they both tend to present the mid-range either more clearly (SW51+) or with more resolution (The Pendant). Perhaps an analogy will suffice here: although the Quicksilver paints with a broader color palette, the individual images of the colors are somewhat more hazy, leading each of them individually to have less fine gradations within them.
Something like the Elekit TU-8800 or 3F will blow the Quicksilver out of the water in their clarity and resolving capacities, but I've found both of these amps to lack the timbral realism of the Quicksilver. For lack of a better term, with both of these amps it has always sounded to me like there is an excessive smoothness and lack of "grit" in mid-range elements. The sound of the quicksilver is more "raw" and "unprocessed" - with the higher-end amps, I felt as if an additional filter had been placed on the sound which, while enhancing many aspects of it (technical and otherwise), rendered timbres a tad artificial. This can be heard particularly, I think, in transient presentation. Though something like the 3F offers faster and more controlled decay as well as more speedy attacks, transients nonetheless lack a certain level of "bite" and sharpness that comes through on the Quicksilver, which to me contributes to a more natural sound.
Treble
Good, but not great. Definitely colored. Seems to have a slight emphasis in the mid-treble particularly, followed by a depression in the upper octave. The SW51+ had more air and a more linear, less splashy treble. The equivalent costing DNA model, the Sonett 2, had much more treble detail and also much smoother, less fatiguing treble. By contrast, the treble of the Quicksilver is very quick, but it also tends to be somewhat rough sounding. The lack of air combined with the mid-treble splashiness can lead to a somewhat claustrophobic presentation here too.
Despite this, the actual timbre of treble instruments is pretty solid with something like the 650. Treble microdynamics in particular are really excellent, and though it certainly could offer more detail, the overall sense of rhythm and Prat in the treble leads to a sense of engagement and lends music a very boisterous energy. I prefer the treble of this amp to something like the SW51+, and think it trades blows with the ZMF Pendant. Both the 3F and TU-8800 easily best it.
Technicalities
Micro-dynamics are excellent, at the level of the ZMF Pendant but below amps like 3F or Elekit Tu-8800. That being said, it could fool one into thinking it was up there with these amps, because it tends to have a very "High-contrast", lively sound which tends to exaggerate differences between different instruments. As a result of this, along with the issues in both the bass and treble, the overall sound can be somewhat disjointed and lack cohesiveness, but oddly enough, I think this can contribute to a feeling of "bounciness" and micro-dynamic excitement. Yet when listening closely, it doesn't really resolve those very small microdynamic differences at the level of a TotL amp. Macrodynamics, meanwhile, are good, but not as good as micro-dynamics. They're much more evident in the mid-range and treble than in the bass, which tends to be a weak point. A step up from the SW51+ here, but doesn't quite reach the level of the Pendant. It doesn't really slam.
Let's talk about soundstage and imaging. This is where the amp impressed me most. I generally don't care about stage, but this amp's stage was definitely a strong point. I don't recall hearing any amp that made the HD650 have this deep of a stage and that threw as much space as it did between instruments while still retaining a solid center image. This was pretty damn impressive. That being said, imaging isn't fantastic - as I wrote earlier, instrument images can be a bit hazy and ill-defined, and though they have a very nifty dimensional effect which makes them sound more realistic, this still applies even with rolling in NOS tubes.
Resolution is, as I've already written, mediocre. Micro-detail in particular just seems to be smeared over by the amp, and when combined with the ill-defined images and the bloom in the lower-mids, this leads the amp to often sound just a bit hazy. This isn't a "Muddy" sound, though - the overall FR, is if anything, upsloping, so it is more akin to the haze of the Valhalla 2 than anything else (though not nearly that bad). The SW51+ honestly struck me as having more clarity, and perhaps a tad more resolve.
Overall Presentation
The Quicksilver is, despite all its problems, a really fun amp to listen to. It has a great sense of Prat, and its transient presentation in particular, which emphasizes biting but not overly sharp attacks with long but not uncontrolled decay, leads to a sound that keeps one on the edge of one's seat. It pairs absolutely fantastically with the HD650, giving its mid-range a sense of visceral immediacy that is often utterly captivating (Some might even call this -boxy-, and I have a preference for an elevated mid-range, so keep that in account).
Yes, it is not a perfect sounding amp, and in many respects, it might even be considered a flavor amp because of its deficiencies in the treble and bass. But for those for whom music lives in the mid-range, the Quicksilver offers more than a mere glimpse of the way TotL amp's present those crucial mid-range textures. Here, it offers a consistently exciting listen with a wonderful balance of crunch and body, and a quickness and rhythm that makes it all too easy to get lost in one's music.
