Grimm MU1

Sell your CD player?

Now, to get back to Ben’s claim that the MU1 is worth selling your CD player for. Is it? For the most part, yes, indeed. The MU1’s performance is so superb that it’s a no-brainer. That said, if I’m honest, I must admit that even the MU1 does not sound entirely identical to the best CD transport that I have available. The MU1 certainly performs equally as well in the familiar audiophile parameters such as transparency, refinement, speed, dynamics, or even resolution. Actually, many CD transports will struggle to scrape the amounts of detail off the disc that the MU1 is capable of. But what CD, when done right, can still add is more depth and flow. But fair is fair, the difference has become smaller than with any server that I heard before.

All this left me wondering how the Grimm team managed to combine all these traits in a single device. I asked and the answer was, somewhat evasively, “you have to know what to measure for”. Personally, I think it has a lot to do with the FPGA board and the Grimm Audio clock, as well as the power supply. Inside is a custom-made switching power supply and although the principle is far from unique, it takes deep knowledge to make one that performs superbly while not contaminating its host or other components in the system with noise. Evidently, the Grimm Audio team has taken great care in designing and implementing this part.

Oversampling

The MU1 can be set to Original, 2x, and 4x. The differences are easy to hear and I had a clear preference for the highest setting. Original provides a “squarer”, more “normal”, relatively direct-coupled, and earthy sound that I find attractive for its superb bass precision. But along with the earthiness comes a dulling in the high frequencies and a much more compact soundstage.  Actually, compared to other digital sources, it’s fair to say that the MU1 with 4x Oversampling provides more air than is strictly neutral. But along with this also comes its organic quality, the extra refinement, and the deeper and wider imaging that sets the MU1 apart from most other servers. More importantly, I find that it most resembles CD playback when set to 4x Oversampling. And most importantly, the airier presentation is provided without the treble sounding tipped up in any way.

The 2x setting lands precisely in between the two other settings with enhanced refinement and fluidity with a moderate amount of smoothness compared to the Original setting (no Oversampling) but less lush and refined and spacious than with the 4x setting.

Mola-Mola Tambaqui

Simultaneous with the MU1, I also had the Mola-Mola Tambaqui DAC on review. As this DAC has its own review I won’t go into specifics here, but suffice to say that this unassuming little DAC is something special! Not only does it sound superb, but it also pairs very well with the MU1.

Inputs

When routing well-known digital sources through the MU1, they receive the same benefits as described in the Oversampling section above. While that can have a desirable result, I also found that some of the original component’s character was diminished when routed through the MU1. For instance, when connecting three sources with very different sonic characters such as the Zanden 2000 CD transport, the Aqua LinQ network transport, or a Spectral SDR3000 CD transport, their relative differences were lessened and smoothed, and mixed with the Grimm benefits. Meanwhile, none of the sources sounded as superb as the internal Roon server. Thus, the decision to use the external inputs will be a personal one.

S/PDIF output

After I finished writing this review, Grimm issued the news that they will add a cinch S/PDIF output to all MU1 units, in addition to the pair of AES/EBU outputs that it currently has. Alas, this change cannot be retrofitted to older models.

Update June 21, 2021 – Updated MU1 hardware

While the Grimm Audio team worked on implementing the S/PDIF upgrade, Bert Bazuin of Terrason Audio, the Dutch distributor for Grimm, kindly agreed to let me keep the series 002 demo unit for a while to enable further comparisons. Last week, Bert called me up to let me know that the work on the new model was complete and the unit was now available. And sure enough, a couple of days ago, a box arrived with in it a brand-new series 003 MU1 unit for me to assess. The reason for this extra comparison is that along with the S/PDIF hardware update, Grimm has also tweaked some of the internal hardware and has found ways to further reduce the jitter as measured in various locations, even if it was already extremely low.

Although the S/PDIF output is physically available on my sample, it is not yet enabled in the software. This will follow later as part of a software update.

Comparing the two units side by side (using two Roon accounts) with the CH C1 DAC and two Jorma AES/EBU cables, to my surprise, the new series 003 unit does indeed have an even denser, more direct,  and more impactful delivery. Remarkably, even though the initial series 002 review model was already benchmark-setting in terms of bass quality and dynamic impact, the new model simply has an even more robust sound!

The bass now has an impressive “chiseled-from-granite” quality while the midrange has an even more energetic, direct, and propulsive feel which combines to an even more visceral and communicative delivery with an even higher jump factor. For me and with my system, this translates to an even more robust and engagingly “live” sound than with the earlier model or any of my other server/streamer solutions.

On a relative note, with this change, the MU1 has shifted its presentation away from gently smooth and organic to what I regard as a cleaner, more direct, and more exciting delivery while retaining the musicality and still involving me emotionally. Depending on the individual’s views, however, it can be argued that this change has also made the MU1 sound relatively drier and lose some of its warmth and flow.

Altered character and personal preferences aside, after having compared the two versions for days on end, the updated series 003 MU1 frequently had me excited. But I also cannot fault the earlier model’s interpretation. Bottom line, both servers perform absolutely magnificently in their own right and I could very happily live with either.

Owners of older MU1’s should definitely not feel short-changed by missing out on this latest update, but all the same, people contemplating getting a MU1 now should feel confident that they are getting the best the firm has to offer.

Needless to say, in either version, Highly Recommended!

Update 11-09-2021 – Remote Control Functionality

Grimm is working on IR remote control functionality that enables switching inputs as well as transport functions such as play/pause, previous, and next.

Software version 1.3.0 has now been released, which adds IR remote control functionality. However, there are no further instructions, so I took it upon myself to try and make this work. As I found, the MU1 unit does not contain an IR receiver, so you’ll have to add this in the shape of an external “eye” with a cable that connects to the MU1’s back, like the one shown below.

Link to item on Bol.com

Then, it’s a matter of choosing the desired function on the MU1 on the IR setup page, pointing any remote control handset to the receiver, and pressing the desired button. Repeat for all the required functions.

For detailed instructions, see the MU1 tips & tricks video on the HFA YouTube channel.

Update 19-10-2021

Grimm Audio has officially announced the new software that enables IR Remote Control, as well as the S/PDIF output, apparently. I have just tested this and indeed, it works in parallel with the AES/EBU outputs, and without having to make any settings. Please find all the official information below.

We are pleased to let you know that new firmware for the MU1 is released. Version v1.3 adds two features that were in strong demand: an S/PDIF output and IR control. The RCA S/PDIF output that can be found on the latest batch of MU1 hardware is enabled. Customers can now use their favorite RCA S/PDIF cable. 

The other feature also enables a MU1 hardware connector: the 3.5mm ‘remote control’ jack on the back, designed for use with common infrared extenders. IR remotes now offer access to play/pause, volume, source selection, previous/next track, and in/out standby. Our team took this assignment serious and the MU1 can therefore be used with any type of IR remote handset on the market. In case you find a remote that does not work, please let us know.

The MU1 software manual provides instructions for programming the IR function. For a good impression, watch the nice YouTube video that MU1 customer and Hifi-Advice author Christiaan Punter made. Enjoy!

Conclusion

The beauty of the MU1’s sonic presentation is that it is tight, precise, articulate, and very highly resolving whilst simultaneously avoiding sounding dry or clinical. On the contrary, the MU1 has a timbrally rich tonality and superb fluidity with a tiny hint of smoothness but without any dilution or smear. Additionally, the MU1 has a captivating  3D portrayal and sense of flow, along with the kind of organic presentation that makes it not only a very accurate Music Server but a highly involving, emotion-inducing Music Machine.

Update 05-05-2024

About one year after I finished this review, Grimm released a big firmware update that improved the Oversampling filter behavior. This changed the server’s characteristics, not just when actually using the 2x or 4x settings but also when using the “No oversampling” setting. This update had a significant impact, enhancing refinement, delicacy, transparency, and precision. For the most part, I felt this was an improvement, although it did mildly reduce the player’s overall liveliness and expression. Grimm released further smaller updates that introduced helpful new features without changing the sound.

The initial firmware update ties in with Roon’s ongoing sound quality changes. Over the years, Roon has reduced the intervals at which they release new builds to what feels like an update every month. When I initially reviewed the MU1, I was hugely impressed that it seemed impervious to the Roon characteristics. To my surprise, it did not suffer from the excessive warmth and thickness through the upper bass and lower midrange, which was so familiar to me from all other Roon servers.

The introduction of Roon build 2.0 also introduced the aspects typical of Roon for the MU1. Throughout the successive Roon updates, the presentation has also become more variable. With some Roon builds, the server sounds really great, and with others, not so much. It is the same with any other Roon server, and Grimm is not to blame, although the aforementioned change in the MU1’s filtering does emphasize the differences.

Whereas the MU1 used to be my crispest, liveliest, and most expressive source, it is now superseded by UPnP/MPD in these areas. The CD transport that used to sound mellower than the MU1 now sounds livelier and crisper. Perhaps most telling of all, my DAC is Roon Ready and the MU1 can stream to it directly. Naturally, I tried that as part of this review, only to find that the Grimm sounded much better to me using its AES/EBU output. But now, that situation is reversed. The other side of this is that those who may have initially felt the MU1 to be a little too clean or too dry for their tastes will likely feel differently now. To those, I recommend giving the MU1 another chance.

In summary, the MU1’s sonic balance has changed since I first reviewed it due to firmware updates and ongoing Roon updates, which means that it now requires different tuning.

Aspects that I now pay special attention to in order to achieve the original MU1 performance (as described in this review) as much as possible include using fast and open-sounding solid-core power cables with very low inductance, open and expressive-sounding digital interlinks, placing the server on Ansuz Darkz T2 footers (other direct-coupling footers can also work well), connecting only a single Roon server to the network at a time (or stopping the Roon core on the second server, as a second Roon core will increase the blurring effect), disabling and removing all DSP/MUSE filters in Roon, using a crisp and articulate-sounding network switch (avoiding those that sound ethereal and dreamy), and disconnecting any unneeded components from the network and power supply.

This addendum was added to provide up-to-date information so that prospective buyers can make a fully informed decision.

Importantly, even though it has changed, the MU1 remains my favorite server.

Associated Equipment

Videos on the Hifi-Advice YouTube Channel

How to add Remote Control Functionality to MU1
How Sooloos became Roon
Grimm MU1 and Antipodes K50
HFA Front Page

Try out Roon for yourself

Get Roon 1 month for free

External Links

Manufacturer: Grimm Audio
Distributor for the Benelux: Terrason Audio

Distributor for France: Prestige-audio-diffusion
Contact: Marc Loubeau
Tel : +33(0)6 49 89 68 88
Email: contact@prestige-audio-diffusion.fr
Website: www.prestige-audio-diffusion.fr

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