Review on Metrum Acoustics Amethyst DAC and Ambre

[Metrum Acoustics]

This is a review posted by our customer

Just another client review on the AMBRE and AMETHYST by Metrum Acoustics. This article has been translated from french to english and the original text can be found at http://patatorz.com/…/metrum-acoustics-ambre-amethyst-un-e…/ and was written by Mr. Ludovic Audoin AKA Le Son de chez Patatorz

Metrum Acoustics : Amber & Amethyst, a wonderful set

Following the various tests of the Metrum Acoustics Ambre that I was able to obtain, and having the idea to put again a system around my Sennheiser HD800S headphones, I combined the Ambre with the small headphone amp / dac of Metrum Acoustics: the Amethyst.

This headphone / dac amplifier is designed on the basis of 2 Transient R2R conversion modules (one per channel). Note that these are the latest versions of these proprietary modules (Dac TWO). These modules are associated with an FPGA which allows to regularize the input signal. This DAC is part of the lineage of NOS DAC (NonOver Sampling) (a small article that explains the difference between DAC NOS, Delta-Sigma and DSD). The DAC therefore accepts only PCM-only signals, up to 384kHz in 24bits on the USB, 24bits / 192kHz on the SPDIF RCA input and 24bits / 96kHz on the Toslink.

The headphone amplification section is there to be able to control headsets up to 16 Ohms. It relies on a 30VA power supply similar in design to that of Ambre. Background noise is given for 145db at 2V RMS. This headphone / dac amp does not present an output stage like the TotalDac Twelve MK2 or TotalDac Direct. When using the DAC part, the headphone amplification section is not active and all the power is associated with the conversion part.

The Amethyst, like the higher range dac such as Adagio or Pavane can benefit from a complementary module for the management of the MQA (only streaming on Tidal today). If the module is implanted, only the MQA signals will be processed: all the other signals outside MQA will be directly redirected to the DAC without passing through the MQA module.

In terms of inputs and outputs, the Amethyst has:

an analog output on RCA connectors (2V RMS)
two SPDIF digital inputs on RCA connectors
a digital optical input Toslink
a USB input on the HiFace Two module base

Note that in my case, the USB input has been replaced by an i2s input in order to benefit from this standard / connectivity between Ambre and Amethyst. This connectivity is provided by an ethernet cable with RJ45 connections.

Amethyst is available in black or silver facade. The dimensions and the case are exactly the same as those of Amber, which makes it in aesthetic terms a homogeneous whole. The front panel has 6 LEDs (Coax 1 & 2, Optical, USB and therefore i2S in my case) for the inputs, a "Standby" LED and an "Error" LED. Switching from one source to another is done by pressing the ON / OFF button so that if you want to switch from the USB input to the Coax1 input you will necessarily go through a "Standby" mode: not great when we have several sources. The volume knob, meanwhile, by design only requires that we press on it to see it out and operate easily.

The last guest on the front is the 6.35mm jack that will welcome your headphones. No jack 3.5 mm, which reflects the willingness of Metrum Acoustics to position this headphone / DAC amp on the hifi end of audio equipment.

Sennheiser HD800S headphones with Siltech Duchesse Crown cable
Source: Metrum Acoustics Amber with RoPiee distribution, Picoreplayer, dietpi.
Ethernet cables Pachanko lan-i2s (50cm) and SOtM dCBL-CAT6 HG (20 cm)
SPDIF Coincident Speaker Statement ST-4 Cable with Black Cat Adapters
Coincident Speaker ST-10 power cables on Tomanek power strip
Roon / LMS / UPnP server dedicated to DIY passive PC. Wifi connection another streamer and server.

My experience with dac R2R ladders has never really been a success and this despite the fact that I owned a TotalDac D1 Dual for a few months. The few DACs of this type who came to my home or that I could listen in good conditions (of course the TotalDac, Rockna Wavedream, MSB Analog, Aqua Formula, ..) have always seduced me by their stamps and their heat but also always disappointed by their side "lack of rhythm", attacks, a side plan-plan that does not suit my tastes. In this sense listening to this DAC R2R ladder announced with a lot of a priori.

The listening began after 3 days of break-in of this new product. Restitution stabilized after a few hundred hours. The listening was done first with the SPDIF Coincident Statement cable and the RoPieee distribution delivered with Ambre. These plays were articulated around the following titles:

• Avishai Cohen Triveni : Dark Nights Darker Days
• Christine and the Queens : Paradis Perdus
• Rosemary Standley : la nuit je mens (Alain Bashung)
• Patricia Barber (Titre DSD converti en PCM 24b/176kHz) : Autumn Leaves
• Alisa Weilerstein : Sonata for Solo Cello, Op.8 (Merci à Nicoben pour la découverte)
• Sophie Hunger : Le vent nous portera
• Michel Jonasz : C’est ça le blues

Without making the suspense last, this R2R Ladder-based headphone / dac amplifier has nothing to do with what I've heard in the past (TotalDac, Rockna, Aqua, MSB, ...). The content character of the latter in terms of attacks and finally with a feeling that all titles played the same, is not found at all on this tiny dac. There is a sense of playful music in the renditions which respects the interpretation of the different actors.

In this configuration, I do not feel any limitation in the bandwidth. The sound stage is perfectly transcribed in width and depth, notably on the Jonasz, and the Patricia Barber. The sound image and the quality of the silences make that the recovery of Noir Désir by Sophie Hunger, "the wind will carry us", make it possible to follow perfectly the different game of cymbals and percussions. The dynamic is not behind (around 2.30min on the Wind will carry us or the Patricia Barber with double bass shots 2.02min and 2.19min) and contributes strongly to the jubilant side of these plays. The stamps are "true" and there is no color in the restitution that is transparent across the spectrum. The superb recording Deutsche Grammophon by Alisa Weilerstein is the perfect example (sound recording): rich harmonics, timbres, incarnation, silences, etc .. The Sennheiser is not the most complicated headphones to "drive" and his open side in terms of sound stage is perfectly served by this association amp / dac / streamer.

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[Metrum Acoustics]

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One might think that the restitution can be a little "dry", lacking material, density or even subtlety in the bass. A passage through Christine & the Queens' "Lost Paradise" and Avishei Cohen Triveni's "Dark Nights, Darkest Days" shows just the opposite. The bass are full of subtleties and nuances on both titles and this despite a rather high compression on the "Paradise Lost". The "Dark Nights, Darkest Days" perfectly measures the ability of this system to restore without distortion and difficulty for amplification the bandwidth of this title (Trumpet, bass drum, cymbals).

Comparisons between SPDIF and i2S

While maintaining the same configuration, it is time to move on the restitution on the i2s. I start with the cable Pachanko (Made in Reunion !!!). I was able a few months ago to try an i2s link between a Rockna Wavedream and a Wavedream Net through HDMI cabling. In this configuration, the contribution of the i2s was undeniable on almost all levels: scene, aeration, dynamics. In the case of the Amber / Amethyst configuration, the i2s link is superior without any possible dispute to the SPDIF which nevertheless did not seem to be in difficulty. This results in increased dynamics, better control of pace and attacks and I would say even a background noise still repelled from where, certainly, the best micro dynamics.

The replacement of Pachanko by a SoTM CAT6 HG also contributed to a significant improvement: more material, more density, more emotions especially in the medium. The question that remains unanswered is whether this improvement is related to the intrinsic quality of the SoTM cable or the fact that it is only in 20cm versus the 50cm Pachanko: the length of the i2S link remains an important question regarding the performance. I would have had to test with a SoTM Cat6 HG 50cm that I do not have on hand.

Influence of Ambre distributions

The last step was to compare the influence of different distributions as I was engaged in the test of Ambre. As a reminder, Metrum Acoustics authorizes the opening of the case to install a distribution other than the original on RoPieee and can benefit from servers such as LMS, MPD, UPnP etc ... This opening does not remove the warranty. Metrum Acoustics works to offer optimized distributions by their care. It takes a bit of work (the blue front LED blinks when it's not a RoPieee distribution installed because of Roon's certifications) and should be offered quickly to meet the most cautious and / or refractory users, to install a distribution.

To come back to the distributions, picoreplayer (v4) and RoPiee (v32) have the particularity to load in RAM and thus to limit the addresses between the micro SD card and the Raspberry Pi. I could therefore compare:

UPnP with Dietpi (minimserver on dedicated PC)
Roon bridge on Dietpi (Roon server on dedicated PC)
Squeezelite on Picoreplayer (LMS server on dedicated PC)
Roon in Squeezelite with Picoreplayer (Roon server on dedicated PC)
Roon with RoPieee (Roon server on dedicated PC)

In terms of preference, I find that UPnP and Roon on Dietpi are behind: less dynamic (especially micro dynamic), less fluid. It's hard to make a real distinction between LMS on PicorePlayer or Roon via Squeezelite / Picoreplayer and RoPieee. Being loaded in RAM and using a Kernel RT should help improve the performance of Amber in these configurations. It must be recognized that Roon is slightly more "round" and "warm" with RoPieee and the use of Picoreplayer / Squeezelite in Roon brings my density, material with a bit less roundness.

In short, all this is only a story of taste because, in the absolute, the gaps are tenuous and whatever the configuration restitution is incredibly intoxicating.

CONCLUSIONS

During these tests, we must admit that there are some points that are more surprising than annoying, such as the volume knob or the selection of sources or even the fact that if we do not replace the USB of the Amethyst by i2s the only common connectivity is the SPDIF RCA.

If now we focus on sound reproduction, this combination Ambre / Amethyst is a success. This success becomes total when the i2S link can be used instead of the SPDIF. The ethernet cable providing the link is not foreign to the performance. This association made me completely a priori on DAC R2R Ladders, Metrum Acoustics is definitely in another logic of restitution in comparison to TotalDac, Rockna and others. During these two months of testing I am reconciled with listening to headphones, even if it remains for me a second system that allows you to relax at times when the main system must remain off. RT kernel distributions bring a plus to overall rendering, particularly in terms of fluidity and dynamics.

This Amethyst drives my Sennheiser masterfully, with authority and subtlety offering great tonal and harmonic richness across the spectrum. What more?

Of course, it would have been possible to test this set with other helmets to validate the quality of the Amethyst. Certainly, an article to evolve as meetings and helmets that could pass at home. Meanwhile, Metrum Acoustics is kind enough to lend me a higher DAC range "Pavane". A good way to validate the design of these dac R2R in comparison with my reference system with, in addition, the ability to test the Amber I2S and AES in front of a dCS Network Bride in AES