Grimm Audio MU2 streaming preamplifier
For several months, my wife and I had been living in a cozy studio apartment in New York’s Financial District while our apartment underwent substantial renovations (footnote 1). All the old furniture was sold or donated, and decades of accumulated stuff was subjected to triage (sell, donate, or store). All my audio equipment, parts, and tools suffered the same fate. Downtown, my listening was via pretty decent headphones (B&W Px8, Audeze LCD-XC) connected to a Mytek Brooklyn+ DAC and my PC. Meanwhile, we were very busy shopping to equip the “new” apartment.
I have never really enjoyed headphone listening (and now I know it’s likely I never will), so our recent return home was a relief in so many ways. We still have a “punch list” of things we’re not satisfied with or that simply have not yet been done. Furniture and other appurtenances arrive on someone else’s schedule. And I can’t overnight resurrect a complex and evolving audio system with a new wiring arrangement; nor is it trivial for an apartment dweller to find storage space for all the now-empty cartons.
An all-in-one streamer-DAC-preamp would not have held much appeal for me if my old system was up and running. This, however, was a different time, and I was offered the Grimm MU2 for review with ideal timing. I had just unboxed two of the KEF Blade 2 speakers (the third was still stuffed in a shower stall with other paraphernalia), and I thought I knew where the Benchmark amps were in our basement storage shed. All I had to do was scramble for a few cables, and the MU2 would let me turn on the music in my home for the first time since last Thanksgiving.
What’s new in the MU2?
While unpacking the MU2 and getting all my ducks in a row, I went back and read John Atkinson’s favorable review of the MU1, a task I encourage; doing so will reward readers interested in Grimm’s digital technology. Comparing that information with Grimm’s documentation for the MU2, we learn that the MU2 is an MU1 streamer with an added DAC and a basic analog “preamp” controller, packaged in the same chassis as the MU1.
A few features of the MU1 have been left out of the MU2, including the digital outputs, since why would a digital player with such a sophisticated DAC need digital outputs? (footnote 2)
The best way to understand what the MU2 adds to the MU1 is the block diagram representing the functions of the MU2, where I have outlined the subset of functional elements carried over from the MU1. Common elements include the digital inputs and the FPGA-based hardware that implements Grimm’s “Pure Nyquist” filters (footnote 3). These filters replace standard multistep “on-chip” oversampling filters with FPGA-based, single-step filters running at 128Fs with high precision, supported by a low-jitter master clock.
The major new elements are the “Major DAC,” the analog inputs, and the analog preamp functions consisting of input selection, volume control, and output selection.
Major DAC: Seeking a middle ground among multibit, single-bit, and pulse-width modulation digital-to-analog converters, Grimm developed the Major DAC, which seeks to avoid the unique constraints of each. Using an unusual 11th order noise shaper, the FPGA-based DAC employs 1.5-bit architecture with 16 DAC cells per channel, and it feeds a fully symmetrical analog output stage.
Analog Inputs and Input Selection: In addition to streaming and digital inputs, the MU2 offers one stereo pair each of balanced and unbalanced analog inputs. Add the new volume control and you have a capable “preamp” for a modestly sized but uncompromising modern audio system.
Volume Control: A no-compromise, relay-based volume control assures precise level increments and channel balance at all level settings.
Output Switch: This manual switch allows selection between headphone output and main (XLR and RCA) outputs. When the latter are selected, both are active, but since they are both driven by the same output circuitry, Grimm recommends using only one at a time. The switch is toggled with two brief taps on the control disc.
The only visible evidence of these changes is on the back panel of the MU2, which obviously is different; otherwise, the MU2 is identical to the MU1 except for the color of the does-everything control disc on top, which is now brushed silver instead of bronze.
Regarding that rear panel: On the left, the USB port is above the Ethernet RJ45 port; next, the S/PDIF (on RCA) input is above the TosLink input. Next to that is a single AES3 input, a stereo pair of balanced analog outputs—all XLR—and then four RCA jacks, one pair analog in, the other analog out. Above that is the 6.3mm headphone jack. Finally, on the right, is an IEC power connector, above which is the master power button and a 3.5mm socket for an IR remote sensor (footnote 4).
Out of the box and into my life
The Grimm MU2 is easy to set up considering its sophistication. It comes with a small manual, but I simply put it on a shelf, plugged it in, and connected it to my local network with an Ethernet cable and to my Benchmark AHB2 amplifiers with a pair of XLR cables. Since I had not accessed my NAS (where all the music resides) in months, I also plugged in a portable USB drive with about 2TB of audio files, just to get started.
Did I mention that the MU2 can serve as a Roon server?
After power-up, I went to my iPad, opened up Roon Remote—new users will need to download it—and accessed the MU2’s Roon Core, already installed. Setting it up took me only a minute or two, since I’ve done it many times, but the simple steps illustrated in the Quick Start Manual should get anyone through in less than 10 minutes. You will need a Roon account, and you’ll want to give Roon access to your Tidal and/or Qobuz accounts, if you have them, then point Roon toward your locally networked music files. You must designate the MU2 itself as its own output device. The only novel step is installing the Grimm Audio Extension, if the MU2 screen tells you it needs to be activated. This makes it possible to display track information on the MU2, and it gives the MU2’s large control disc access to Roon.
The MU2 includes all of Roon—the whole feature set— and Roon Remote works perfectly, but Roon has no provision to access analog inputs or to switch between the line or headphone outputs. To accomplish these things, you can use the control disc—or you can use the Grimm UI (GRUI) web interface, which supports selecting inputs (analog, digital, and network) and outputs (line and headphone) and, via submenus, configuring system-startup settings, level offsets for the analog inputs, IR programming, and advanced system operations. The important display of active content info, control of volume, mute, and pause are accessible via the Roon Remote, GRUI, and directly on the MU2 (via its front panel display and control disc).
At first, I worried about that do-everything flying saucer, trained as I am on more traditional single-function knobs, but using it quickly became intuitive, and it was always easy to locate, even in the near dark. Tapping, pressing, and turning the disc was like interacting with one of Felonius Gru, Sr.’s friendly, bouncy minions.
At last!
I could not wait to hear some music, so instead of exploring options or waiting for Roon in the MU2 to process my main library, I directed it to the 2TB portable drive and selected a favorite: Ligeti’s Six Bagatelles for Wind Quintet in a 24/96 remaster from Harmonia Mundi. From the first note—as the five instruments tootled and crooned—they (the instruments) appeared comfortably arrayed across the front of my room, just a short distance behind the speakers. Since this recording incorporates only minimal ambient information, there was a definite illusion of the presence of the instruments in my room. Each was clearly delineated, and the overall balance was neutral, favoring nothing but revealing the full, inherent color and body of the instruments. Depth is not a factor in this recording, but width was appropriate. What a wonderful welcome home; thank you, MU2.
My experience was strikingly different with an interesting arrangement for violin and piano of a suite from Prokofiev’s Romeo and Juliet. Here, with just these two instruments (Lana Trotovsek, Maria Canyigueral. 16/44.1 FLAC download, SOMM SOMMCD 0671), the soundstage is huge. At the start, we hear the violin on the left and fairly close and the piano somewhat farther back on the right. Both are immersed in a space much larger than my listening room, with a warm acoustic ambience that does not obscure them at all. They have good presence and body and a pleasing, natural tonal balance. Apparently, the MU2 does not obscure subtleties of instrument placement or acoustics.
Footnote 1: The work does include substantial in-wall rewiring for AC, Ethernet, and extensive CAT6-based audio connections.
Footnote 2: I remain curious about the MU1’s ability to support multichannel using the dedicated LS1 output or S/PDIF RCA and the two AES3 outputs but these went away with the digital outputs.
Footnote 3: Since there are no digital outputs on the MU2, there are no longer options for up/downsampling or DSD-to-PCM conversion.
Footnote 4: The MU2 does not come with a remote control, but for those who want to use one this sensor allows the user to connect and program a wide range of RCs. I saw no need to attempt this as smartphone/tablet control is better.
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Grimm Audio BV
Veldhoven
The Netherlands
(+31) 40 213 1562
grimmaudio.com
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