Perfect Sound Forever, All Else is Gaslight

These phrases greeted the introduction of domestic digital music to consumers in 1982.

I immediately went out and bought a Philips CD104 player.

I played the sampler disc and WOW. No crackles, no clicks, no pops. An even frequency response with great tight fast bass. Superb measurements. This is the sound of the recording studio.

No wow, no flutter and…….no music.

OK, it could be a badly recorded disc.

But no, the music was absent from nearly all of the discs. The sound quality was great but the music…..missing in action.

Time marched on and engineers who understood that digital presented different problems to analogue also needed different solutions. Some issues were solved quickly and others took much, much longer, even decades. Analogue companies took great delight in advertising this problem, like the infamous Linn campaign…is this a lemon, with an image of a lemon? Linn was half right, something was amiss as this was not an exact copy of the recorded music, the soul and the heart of the music were missing.

After many years of development, there seemed to be a truce where digital was described as being different to analogue, therefore it was not wrong, just different.

Then along came newer engineers who approached the problem differently. Even Linn had Gilhad Tiefenbrun who came in and designed a complete range of streamers that got rid of many problems and even used switched-mode power supplies. And later on, newer names appeared such as Rob Watts and Bruno Putzeys who made great inroads into the problems with digital. Also, others like Guido Tent designed essential parts of the digital circuitry (crystal clocks) to eliminate other problems. These people brought new and better solutions for dealing with digital replay (and recording). And eventually, the normally conservative (small c) audio community started to accept that digital could produce much better sound than the bad, early players. It was not perfect and guess what, some discs did not last forever.

But the rumours abounded. You could pass a digital signal through a coat hanger and get a sound out of the end (awful sound?). Proof that digital signals were extremely robust. Digital Audio is digital therefore it MUST work. Your computer sends digital picture data to a printer and out the image pops; it is digital and it works. But could they be different forms of digital asked the newer digital engineers? They did not just shout it is digital, measures perfectly and is therefore perfect. They actually listened, investigated and solved problems and made real progress.

Another fable said: look, if a CD is 16/44.1 there is a limit to the sound quality you can get (true), therefore the perfect CD can never be improved. End of discussion. But no, progress was made and people understood jitter, digital noise and other problems and their solutions. And here is the latest solution to those ills in one package, the GRIMM MU1 digital music source.

The Grimm MU1 digital music source is one of those products that have come along and challenged all those fables and (giving the game away) improve the sound quality of bog-standard CD, in a big way. I can’t resist the temptation to use the phrase, so will not, it makes the sound more analogue and human. No not like a high-quality turntable, but with the best audio from a turntable mixed with the best from digital. The sound has great 3D, natural-sounding music with great flow mixed in with tight, fast bass that sounds as though it has been played by a human.

Enough of the generalities, how has GRIMM achieved this with the MU1?


The GRIMM MU1 has been designed by a team of excellent audio engineers who got together after recognising kindred spirits and originally consisted of Eelco Grimm, Bruno Putzeys, Guido Tent and Peter v Willenswaard. Bruno had left the company and the others brought their expertise to build a new type of digital front end. The design is based on what they heard via listening tests and resulted in some unusual solutions that challenged commonly held beliefs. The GRIMM MU1 uses a switch-mode power supply, which is very low in electrical and radio frequency noise. The original bugbear of switching noise is very low because of careful and thorough design. Forget wall warts, they are cheap and nasty things, the one in the MU1 is one of the best.



Many audio companies now use switched-mode power supplies because they are very low in noise, efficient and low in weight. With careful design, high audio quality can be achieved when the engineers know about digital circuits and their impacts on audio.

For the digital audio circuits, GRIMM found the digital signal is very sensitive to tiny changes in the timing of the signal, jitter. So much so that they say it is essential for the clock in the DAC to be locked to the clock in the MU1. They believe that the clock used in the GRIMM MU1 is far more stable than most of the clocks used in a lot of DACs. The easiest way to achieve this was to link the GRIMM MU1 and the DAC via a cable and send the clock signal from the GRIMM MU1 to the DAC. This is not possible with USB so ruled out that very popular connection. I2S could have been used but there is no clear standard so is not used. That leaves the balanced AES/EBU and unbalanced S/PDIF connections. These connections carry a clock signal to the DAC and can lock the two clocks together. GRIMM, therefore, recommends using AES/EBU or S/PDIF as the best connection. As Guido Tent was involved with the GRIMM MU1 the stability of the clock in the MU1 will certainly be one of the best out there. It is already used in studio applications.

Listening tests also showed the sound quality improved if the original signal was upsampled. GRIMM recommends upsampling 16/44.1 digital to 24/176 (4x) and for that digital signal to be sent via the AES/EBU cable to the DAC. If the input signal is 16/48 then that signal is upsampled to 24/192, which is the limit of what the AES/EBU cable can use. But what happens to higher-resolution signals or DSD music? That is converted to 192kHz or 176kHz to travel along the AES/EBU cable. But don’t you lose sound quality by downsampling to lower-resolution audio? Eelco Grimm says yes but it is a small loss compared to the major gain of getting the GRIMM MU1 and DAC clocks locked together.


GRIMM MU1 Playing DXD​

Wanting to control all of the audio processing and ensure it is done properly, the upsampling or conversion is done in the GRIMM MU1 using an FPGA chip that GRIMM has programmed. FPGAs are well suited to do many calculations with great precision. GRIMM are aware of other upsampling software players but argues that the GRIMM MU1 is far more precise.


So the main (and important) part of the MU1 is not just the hardware but the software encoded into the i-3 computer and the FPGA. This software represents nearly 8 years of effort from some of the leading digital engineers in audio.

OK, but does it do the job? What does the GRIMM MU1 do?

It takes a digital music signal, processes it and feeds out the cleaned-up digital signal to a DAC, getting rid of nearly all the digital problems in between.

To use the MU1 you must have Roon to control and play your music. I have to admit I like Roon as a music system as does Mr Underhill who reviewed the Roon system here: At the moment there is no alternative to Roon, although GRIMM has said they are working on a UPnP renderer interface. Using Roon, the MU1 is a digital player of your local files. It can also be a streamer and play Qobuz and Tidal music services, and the MU1 has a lossless digital volume control and thus can be a digital preamplifier. It is a digital upsampler and has a built-in Roon Core on the internal i-3 computer. As an option, you can add internal music storage.

The GRIMM MU1 is a buff black box with a large copper-coloured disc that provides an unusual interface between the user and the GRIMM MU1. There is an APP that controls the GRIMM MU1 and I have to admit I mainly used the APP. When I used the copper disc, I had to have the manual nearby, especially when doing something more complex than changing volume, input, or muting.


The GRIMM MU1 has AES/EBU, S/PDIF and optical digital inputs. It supports all audio digital formats. It has two AES/EBU and one S/PDIF output. There is an input for Ethernet using an RJ45 socket. The APP is a web-based control interface.

And how was the sound quality? To test how it sounded I fed the Grimm MU1 via a Cat 6 cable using a 100 Mb/sec network connection. The AES output signal was fed into a Mola Mola Tambaqui DAC by an Audioquest Diamond cable. The balanced output from the Tambaqui went into my Luxman 900 pre and power amplifier or the ARC Ref 6SE and ARC 75SE. The sound came into the room via Avalon PM1 speakers. The amplifier and speaker cables were from Cut Loose Audio. The system has Quiescent Couplers and mains cables with Ultimate mains cables from Puritan powering the amplifiers. I also had a Jays Audio CD2 Mk III transport feeding an AES signal to the DAC via a Gothic Audio silver cable.

On goes my usual tracks to test all aspects of the audio and… The first track was the Game of Thrones medley by 2 Cellos, the duo -- Luka Šulić and Stjepan Hauser -- play a Game of Thrones medley with the London Symphony Orchestra. This cover is subtler than others and starts with a gentle introduction and as the track proceeds the music becomes more intense and the LSO add a lot more drama to the music. The MU1 managed to keep the sheer intensity of this track without it sounding uncomfortable or having any digital edge. It was easier to listen into the music and hear the technique of these classically trained musicians. A great start.

As a complete contrast, I play Birmingham Sunday by Rhiannon Giddens from Freedom Highway. Birmingham Sunday is a song written by Richard Farina and initially performed by both Fariña and his sister-in-law Joan Baez. The subject matter is the bombing of the 16th Street Baptist Church on September 15, 1963, by members of the Ku Klux Klan that killed four girls and injured 22 others. Giddens sings it with great emotion and anger which the MU1 allows to come through. Her voice is very powerful and is in contrast to the melody that comes from a Scottish ballad, I once loved a Lass. This is a moving song and that comes through, clearly.

On to Did Trouble Me from Praise & Blame by Tom Jones, released on 26 July 2010. This was his 38th album and his first release with Island Records and was recorded in 2009 at the Real World Studios in Wiltshire. It was produced by Ethan Johns and made up of little-known devotional and gospel covers. It is in complete contrast to his usual schmaltzy recordings and features T. Bone Burnett with a cut-down production and a few added extras, but no full orchestra. This track was written by Susan Werner a US folk singer. The track features Jones’s powerful voice, centre stage. There he is present in my room with a small and sparse backing group enough to support Tom but not detract from his singing. The MU1 made it difficult not to fall into the music or get distracted by writing notes.

A complete change of mood, Dazed and Confused by Led Zeppelin from their first album. This track was written by Jake Holmes who says it was about an indecisive girl not ending a relationship but folklore says it was about a bad acid trip. The Yardbirds heard the song and made it their centrepiece with Jimmy Page producing one of their recordings. Jimmy reworked the song and it was included on their first album and it became their signature song. The reasons are clearly here to hear, with a gentle start and effects sweeping between channels and building up the intensity with some simple well-timed bass playing from J P Jones. The track continues to build in intensity with Robert Plant singing and then wailing about this indecisive girl with great guitar overlays and really powerful drumming from Bonzo. I normally use this track to test whether an audio item can ROCK. The GRIMM MU1 was unusual in that it portrayed a very detailed and integrated piece of music with real power behind it. There are a lot of digital products that can sound very detailed but are not that powerful. Or the reverse. But here it is both.

OK let’s try some BIG sounding music. 2049 from Hans Zimmer and Beethoven’s 9th finale (the Reference Recording of the Pittsburgh Symphony Orchestra). 2049 starts with electronic deep bass. With the GRIMM MU1 it was easy to hear the changes in bass frequencies and tone and how they change their position on a huge 3D soundstage. The GRIMM MU1 played with real power and depth and lets you know that there was something big, powerful and menacing coming soon. It presented the details, with the drama of the music. For Beethoven, the music starts dramatically and only as Beethoven could with great power. The music shocks and the slightly more forward sound of the recording also comes through. Some people prefer a more distant sound from a more mid-hall sound. This recording is a few rows further forward and it was easy to enjoy the power of a full orchestra or ‘zoom’ in and listen to individual instruments playing. But when the orchestra was going full tilt with the Mendelssohn Choir of Pittsburgh under the baton of Manfred Honeck it was difficult not to get overwhelmed with the sheer power of the music. And no digital nasties were present. WOW again.

When I compared my various digital front ends, I doubted I could tell a difference between music streamed and that played from locally sourced files. The GRIMM MU1 was doing its job and there are now more differences from the origins of the source material than the GRIMM MU1. I am now happy to listen to either my recorded music or that streamed by Qobuz. That is significant progress considering the many extra miles the streamed music has to travel. How about CDs played locally? Hardly that much difference and I was happy with either. Vinyl was closer and my preferences changed for a lot of albums, which again may be due to original recording source differences.

OK summarising, this digital front end is the best I have heard and worked exceptionally well with the Mola Mola Tambaqui. It shows how far digital has come, and the expertise and skills of these engineers. Yes, it is expensive at £12,000. But it is far more than a computer, a sound card and a fancy power supply, it is the distillation of 8 years of work from a team of top-grade engineers. And for me, it is one of the best digital front ends out there.

It is without a doubt, a world-class digital front end. I could not let it go, so I bought it. If you want one of the best, this is it.


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