Grimm Audio MU1 music streamer Page 2

Learning how to use the wheel didn't take long, and the inconvenience of having to walk over to the MU1 wasn't a problem given that almost all the operations it enables are "set'n'forget."

Since I purchased the review sample, along with a lifetime subscription to Roon, the Roon Labs Nucleus+ music server ($2559) has been my primary source for digital music. I have been using it with network-connected D/A processors that can act as a Roon endpoint, like the PS Audio DirectStream and MBL N31. I am currently without a NAS drive, so Roon accesses my music library via an internal drive I installed in the Nucleus+.

Eelco Grimm had warned me that having two Roon Cores on my network might lead to problems, so before I set up the MU1, I turned off the Nucleus+. Once the MU1 was powered up and connected to my router, it was recognized by the Roon Server app. I clicked on the on-screen "Connect" button and configured the Grimm Core with Roon's Audio Settings menu (footnote 2).


An internal SSD drive for music file storage can be installed when the MU1 is ordered. The review sample was fitted with a 1TB SSD (a very reasonable $225), but for convenience I plugged a 2TB hard drive that already carried a copy of my music library into one of the Grimm's USB ports and selected it with Roon. As always, I was astonished by the speed with which Roon catalogued the library and downloaded the metadata for each file.

For my initial auditioning, I selected the network-connected MBL N31 DAC as Roon's active Audio Zone, which I had previously been using with the Nucleus+. (The MBL's reconstruction filter was set to minimum phase, which I preferred overall.) Playing a variety of my favorite tracks sourced from the Grimm MU1, with the rest of the system comprising the Pass Labs XP-32 preamplifier that I review elsewhere in this issue, Parasound Halo JC 1+ monoblocks, and my KEF LS50 loudspeakers, the sound was basically both excellent and indistinguishable from what I was used to with the Nucleus+ sending network data to the MBL.

However, what distinguishes the MU1 from the less expensive server is the upsampling function that can be applied to its AES/EBU outputs, though not to the network or USB outputs. I selected 4× upsampling with the Grimm's wheel, connected one of the AES/EBU outputs to the MBL's AES/EBU input with a 15' length of Canare 110 ohm balanced digital interconnect, and selected the MU1 as the Roon endpoint. I started playing a CD-resolution file, and the MBL's display confirmed that it was receiving a 24-bit/176.4kHz stream.

Oh my!


I had been playing one of my favorite performances of Rachmaninoff's Piano Concerto No.2, with Vladimir Ashkenazy accompanied by Bernard Haitink conducting the Concertgebouw Orchestra (16/44.1 ALAC file ripped from CD, Decca 4757550). An early digital recording—it was released in 1986—the sound via the MU1's network connection was somewhat congested, with limited soundstage depth. The same recording, upsampled to 176.4kHz and sent to the MBL DAC via the MU1's AES/EBU connection, was dramatically better. The tonal balance was still warm, but the congestion was reduced, adding depth to the soundstage and increasing the separation between instruments and groups of instruments within that stage. Even lossy-compressed audio, like the 128kbps stream of BBC Radio 3's Night Tracks program, to which I have become addicted, benefited from the MU1's upsampling.

I continued my auditioning with upsampled CD-resolution files and found that there was an engaging quality to the presentation. "Just one more track," I found myself muttering to myself when dinnertime loomed. But what about the sound quality with audio with greater bit depths and higher sample rates than 16/44.1?

I selected "The Trader" from the Beach Boys' 1973 Holland album, which I had ripped to a 24/192 PCM ALAC file. Now that was intriguing. Even though I had the volume control for the AES/EBU outputs disabled, which means that the MU1 was simply passing the data unchanged to the DAC, the sound was noticeably more palpable, with a better sense of rhythm, than the network connection. I had the same experience with DSD-encoded files, like Christian Tetzlaff and Lars Vogt's superbly idiomatic recording of the Brahms Violin Sonatas (DSD128, Ondine/HDtracks ODE1284-2D). There was simply more there there with the AES/EBU outputs.

Digital inputs
I finished auditioning the MU1 by trying its digital inputs. I retrieved my Astell&Kern AK100 portable media player, reviewed in August 2013, from the desk drawer it had been living in since I replaced it with a PonoPlayer. The AK100's 3.5mm headphone jack doubles as an optical data output.


The AK100's TosLink output has relatively high jitter, but with the MU1 upsampling and dejittering data, I again experienced that improved sense of connection with the music, not only with 16/44.1 data but also with hi-rez files. I selected Daft Punk's "Lose Yourself to Dance" (24/88.2 ALAC from Random Access Memories, Columbia/HDtracks) and pressed Play. I never had difficulty losing myself with this track, but with the data upsampled to 176.4kHz, I had to dance.

Summing up
At $10,500 without internal storage, the Grimm MU1 is expensive. However, it is only slightly more so than the Wolf Audio Systems Alpha 3 SX ($9295–$9895) Jason Victor Serinus reviewed in May 2020. And it is not as wallet-straining as the Innuos Statement ($13,750) Jason reviewed in April 2020 or the Pink Faun 2.16x ($20,750) Kalman Rubinson reviewed in December 2020. With its digital inputs and high-precision volume control for its AES/EBU outputs, the Grimm MU1 is not just a streamer; it is a digital-domain preamplifier that can be connected via a D/A processor to a power amplifier. The MU1 incorporates a Roon Core, can operate as a network bridge with legacy D/A processors that don't have USB or Ethernet ports, and can be used as the sole source component with active speakers with digital inputs, like the Kii Three, Dutch & Dutch 8c, and Grimm's own LS1. And, especially via its upsampled AES/EBU outputs, it sounds superb. For those who can afford it, the Grimm MU1 is a highly recommended digital audio solution.

Footnote 2: The Grimm website includes a useful page listing known issues and their solutions.
Grimm Audio BV
The Netherlands
(+31) 40 213 1562

dumbordumber's picture

A lot appears to have been spent on the casing of this item, particularly the top. However, the interior is a very different kettle of fish. It looks lashed together. Standard length cables, folded and cable-tied. The DC, digital and signal cables are all unprotected from RF and EMI. The casing interior has no damping of any sort, no special layout, or suspension of circuit boards, just old-school steel pillars. In fact the interior of this device largely looks like a computer that has been assembled from fairly standard off-the-shelf components by your local computer shop. I have no doubt that it sounds good if those components are well matched and well chosen, and if the power supplies are decent. But so do many home built computers costing far less. This really is a lamb in wolf's clothing.
If I had bought this device and not known what was inside, I would have been expecting, for the price, something akin to Naim's layout and military wiring. If I had opened it up and found what lay inside, my face would have looked...well, Grim.

Jack L's picture


I concur with yr candid comment: "grim" - uninviting !

It should sound superb as reflected from its lofty price. Yet its so-so internal fabrication looks like some "of-the-shelf" stuff built by a neighbourhood computer repair shop. Hopefully it's actually "a lamb in wolf's clothing" !!

I said so from my recent experience. Just 2 weeks back I got a very basic DAC of an audio unknown brand-name in New York for an unbelievable very dirt crappie price from Amazon.

I acquired it sorta for 'fun' as digital is always my back burner music source vs vinyl classical music I addicted to.

It got basic Toslink & coaxial input & unbalanced RCA audio O/P & earphone jack featuring no-joke 24bit 192KHz sampling rate with 3 year free warranty.

Beyond my expectation for such crappie price, this New Yorker sounds pretty decent with its coaxial input & audio O/P hooked up to my design/built phono-linestage with straight-line bypass mode ON.

This Little David from New York makes ALL my CDs & DVDs sound so much better than before ! WoW. So pleasantly surprised !!

Play digital smart, dear consumers !

Listening is believing

Jack L

Jack L's picture


Despite its very dirt cheapie price vs it's decent sound, this litte no-name New Yorker DAC is built in a small all-aluminum box so rigid & strong with 'seamless' corner joints looked like 100% watertight !!!!

So gratified !

Jack L

mememe2's picture

"$10,500 without internal storage". Two hoary homilies come to mind - 1. More money than brains and 2. You can put lipstick on a pig but it's still just a pig.

cgh's picture

Knowing nothing about the manufacturing process I was surprised, many years ago, to learn how expensive it is to make the box. I happened to be at a manufacturer's plant in CO after a RMAF when these parts came back from being dipped in acid and anodized.

Anyway, that's an attractive box IMO. The top reminds me of those popular pictures attempting to explain general relativity (curvature related to stress energy). Guessing it isn't cheap to make.

Jack L's picture


So comparing the "off-the-shelf" like fabrication quality of its inart, how much as a consumer like you, would guess to pay for the for the box alone ? Say 60% ??

Are we paying our hard-erned money for the music or its "attractive" box ?

By the same token, the dirt dirt cheap price I paid for my basic 24bit192KHz DAC of New York which sounds so decent, is built in a small "water-tight" aluminum box strong & rigid like a miniature tank. Where the manufacturer got the money to cover the cost of the box alone ??

Jack L

Jack L's picture


So comparing the "off-the-shelf" like fabrication quality of its inart, how much as a consumer like you, would guess to pay for the for the box alone ? Say 60% ??

Are we paying our hard-erned money for the music or its "attractive" box ?

By the same token, the dirt dirt cheap price I paid for my basic 24bit192KHz DAC of New York which sounds so decent, is built in a small "water-tight" aluminum box strong & rigid like a miniature tank. Where the manufacturer got the money to cover the cost of the box alone ??

Jack L

partain's picture

Unlike in the political universe , where never do promises of benefits "trickling down" come to fruition , Trickling down is inevitable in electronics.
Good thing.
I'd be willing to pay $700.00 , or so .

AaronGarrett's picture

I have one and my experience exactly mirrors JA. On low resolution material like streaming radio, which I listen to a lot, the difference is enormous upsampled via AES/EBU. Stuff I couldn't listen to I now really enjoy. For me this alone is worth it, I can enjoy a lot more music than I could without the MU-1. In addition for Native DSD it is great. And although JA didn't mention it (because it is not presently a feature) it will be able to do FM radio as well and be a very full-functioning digital preamp.

But as JA says also there are a lot of other very serviceable and cheaper solutions if this isn't an issue for you.

davemill's picture

I am looking forward to the release of the Boulder 812 which will additional provide balanced analog inputs and will be at a LOWER price point. I refuse to spent that amount for this type of device unless it is engineered and manufactured in the US which the 812will be and will no doubt perform extraordinary well.

Dear Stereophile Administrator, the CAPCHA authentication process at least for MacOS and iOS devices using Safari needs to be fixed. For at least six months, I have always had to use the forgotten password process to log in even though I am entering the correct password. This is a security issue.

Foottapper's picture

Hi John, thanks for the review. Since a couple of months I’m thrilled to have the MU1 at home, just love the ease of use ánd jaw dropping sound. Any chance that you’ll review the LS1be’s?