Grimm MU2

Running In

When I received the review unit, another reviewer had already used it, meaning it was likely already run-in. Nevertheless, since it arrived in an ice-cold state, I left it for two days to unfreeze before switching it on. Then, I let it acclimatize for several more days before listening for the first time. After that, I let it run for over a week before listening again. When I listened to it again, I did not note any sonic differences, which indicated that the MU2 was now at a stable point of operation.

I listened to the MU2 on Artesania and HRS racks, and while there are differences in certain areas, it performs very well on both.

Review Context

The MU2 will be listened to in the context of the main system, which consists of the CH Precision L1 preamplifier, CH Precision A1.5 power amp, and Magico S1 MkII speakers. Other digital sources include the Grimm MU1 and Antipodes Oladra Music Servers, the Aqua LinQ streaming endpoint, and the Aqua La Diva M2 CD transport. Available DACs for comparison include the CH Precision C1.2 and Aqua Formula xHD.

I listened to the MU2 on an HRS EXR audio stand, with a range of footers, and on an Artesania Aire floor platform with Carbon Fiber Linear Arms and KSH2 Krion shelves.

Listening

I started listening to the MU2 as an integrated player using local music and Qobuz streaming, and throughout my listening sessions, the main aspect of the MU2’s performance that stands out the most is that it is a thoroughly refined and well-polished machine. It’s got superb resolution but is never braggy about it. It is fabulously linear, neutral, and precise but, at the same time, always pleasant.

More so than the MU1 (using the average result of a range of DACs used), the MU2 is the antithesis of analytical, let alone clinical. No matter what you play, there is never any harshness, edginess, or even remotely stereotypical digital about it. Still, while it sounds very far from cool, I also can’t say the MU2 is warm per se, and it is most definitely not fat. It’s got fluidity, grace, and charm, and its pacing is spot on, always toe-tapping and neither hurried nor slow.

In many ways, the MU2’s DAC section seems to “simply” pick up and continue in the same vein as its server/streamer part after handing over the signal. Like the MU1, the MU2 sounds neutral yet natural, fast and articulate yet fluid, and accurate without sounding tonally lean.

Having heard the MU1 with a wide range of DACs, I will admit I had a preconception of how the MU2 might sound. It’s a bit like envisioning how a person might look based solely on conversations over the phone – not rooted in reality whatsoever! For some reason, I expected the MU2 to be like a MU1 with a Mola Mola Tambaqui DAC in a single enclosure. For better or for worse, it is not. The MU2’s DAC section does not sound like the Tambaqui (which is brighter and more expressive), nor does it sound like the CH C1.2 (more forceful and robust) or the Aqua Formula xHD (more direct and explicit). In fact, I can’t think of any DAC that the MU2 does sound like. Which kind of makes sense, given their unique DAC topology.

But I realize that still does not really describe what the MU2 does sound like. Let’s break it down into smaller segments to describe the MU2’s performance more accurately.

Starting with the low frequencies, I was pleasantly struck by the precision, articulation, and agility of the MU2’s bass performance. It’s never boomy or bombastic; quite the opposite. Some might find the MU2’s bass to be just a tiny bit lean compared to more voluptuous-sounding servers such as those by Antipodes or Taiko Audio, but flat-out describing the MU2 as lean would be a disservice. Nimble and lightfooted is how I would characterize it.

Moving over all the way to the other end of the spectrum, we find treble that is, quite simply, impossible to fault. It’s highly resolving, explicit, delicate, airy, delightfully fluid, and in no way stereotypical “digital”.

In between these extremes is where something special happens. With tight and articulate bass, one might expect the midrange to be lean or desaturated. This is where the MU2 surprises with density, plushness, and bloom, combined with a laidback gentlemanlike behavior. It’s decidedly calm and quite the opposite of upfront, let alone shouty. This makes for a sound unmistakably highly resolving and transparent yet easy on the ears. It’s weird but the MU2 sounds warm without being warm, if that makes any sense. In any event, I found that the MU2 invites long listening sessions and goes about its way almost anonymously, leaving the music to do its thing.

On balance, you could say that the MU2 is positioned between the Grimm MU1 and the Antipodes Oladra. Assuming a neutral DAC is connected, the three servers are more or less equally capable in terms of resolution and precision, but the MU1 presents the music with a slightly leaner tonal balance and slightly more expressive midrange, whereas the Oladra presents the music with a lusher, more euphonic, and more deeply saturated overall balance. Finally, the servers can also be distinguished by their soundstaging. Whereas the MU2 has superb focus, it comes across as a little more compact than the MU1 with either the CH C1.2 or Aqua Formula xHD DAC, while the Oladra (using AES/EBU) projects the widest and deepest soundstage of the three with the same two DACs. That said, the MU2 has absolutely no trouble imaging outside the speakers, but what happens between them tends to be focused, intimate, and precise rather than breathy or expansive.

Of course, these comparisons are highly dependent on the influence of the external DAC and should thus be taken with a good dose of salt, but still, I hope they are useful in describing the MU2’s sound.

MU2 as a DAC

Besides functioning as an all-in-one server and player, the MU2 also accepts external sources, both analog and digital. Importantly, the analog inputs follow a 100% analog path, so they are not digitized. First and foremost, I wanted to test its AES/EBU input. For this, I used an Aqua La Diva M2 CD transport. But before that, I thought it would be interesting to see what would happen if I connected the MU1 to it. Naturally, that is not a normal use case, but it will allow me more insight into how the MU2’s server and DAC sections behave independently.

So, first up for audition was the MU1, feeding the MU2’s AES/EBU input via a Jorma Audio cable. Switching between the MU2’s internal Roon Core and the AES/EBU input can be done via the menu and dial on top, but is made even easier via the web interface that can be accessed via any device that can run a web browser. The server switches instantly and silently and pauses Roon playback when you switch away from it. Playing the same music from the same source and swapping between the two sources initially felt very similar. But upon listening closer, I detected valid differences… in favor of the MU2!

I found the MU1 to be a little more expressive when combined with a range of DACs than the MU2 by itself, but with the MU1 connected through the MU2, it actually worked out the other way around. Now, the MU2 sounded more expansive, more gushing, and more expressive. Otherwise, the level of detail, the transparency, and the overall character were the same. This tells me that the server part of the two MUs is equally capable, but the integral implementation and direct internal connection place the MU2 at an advantage.

Switching to the Aqua La Diva M2 CD Transport as an AES/EBU source and playing the very CD from which the test file was made, the roles are again reversed. This time, the CD transport sounded a little crisper and livelier and, as a result, just a little more engaging. That’s not really a surprise, though, as this transport had impressed me for the same reasons when I reviewed it earlier and compared it to the MU1. The noted difference is partly due to the CD transport’s spritely nature but also partly attributable to the impact of software updates on how Roon sounds. While we would expect updates only to add features or fix certain aspects of the software, the reality is that they often also affect the sound. To my ears, the impact is more than subtle, but the effects are not devastating. At worst, they make the software sound round and friendly. If you never noticed any changes or never paid attention to this, it’s probably safe to assume the impact is not large enough to worry about.

As my final test to assess the MU2’s performance as a DAC, I used the MU1’s double AES/EBU outputs and two Jorma cables and connected them simultaneously to the MU2 and the Aqua Formula xHD DAC. Then, I fed the same Driade Flow Link Reference 808 cables from both devices to the L1 preamplifier. This allowed me to instantly swap between the two sources using my preamp’s remote control.

I set the MU2 to +4dB on its display to match the gain between the two. Note that the scale in the Roon app shows values different from the Grimm itself. For instance, the unity setting of 0dB on the Grimm equals 92 in Roon, while 100 in Roon equals an actual setting of +8dB on the Grimm, which may overload a preamp input.

Incidentally, I used the same setting when directly comparing the sound of the CH C1.2 DAC to that of the MU2. When testing this in both cases, I was happy to find that the volume control operates very transparently. There is no hardening of the treble, no added edge, and no loss of resolution. Just a higher volume and nothing else, just as one would reasonably expect, but which is not always accomplished.

While switching between the Formula xHD and the MU2 as DACs, I heard notable character differences, confirming my earlier feeling that the MU2 was quite calm and gentlemanlike. While the two DACs have comparable transparency and resolution, the Aqua is upfront, explicit, and exciting, while the MU2 is calm, soothing, composed, and comparatively laidback. It’s a divisive matter but also entirely one of personal taste. I personally like music to be expressive with a high jump factor, but I also know this kind of delivery can be experienced as less romantic, hard, or tiring. Ultimately, I can imagine listeners choosing either presentation with equal validity.

What remains is the matter of value. While 18K euro is a small fortune, many servers cost more while not containing a DAC, or a preamp, for that matter. In that light, it can be considered relatively cost-effective. And one should not overlook the convenience of having the entire front end in a small and attractive package.

Speaking of the MU2’s built-in preamp, let’s see how it performs, shall we?

Next: MU2 direct to a Power Amp, Footers, Cables, and Conclusion

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