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.
Listening
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.
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.
ListeningFor 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.
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.
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 upAt $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.
