Reviewer:
Srajan Ebaen
Financial interests: click here
Sources: 27" iMac with 5K Retina display, 4GHz quad-core engine with 4.4GHz turbo boost, 3TB Fusion Drive, 16GB SDRAM, OSX Yosemite, PureMusic 3.01, Tidal & Qobuz lossless streaming, COS Engineering D1 & H1, AURALiC Vega, Aqua Hifi Formula, Fore Audio DAISy 1, Apple iPod Classic 160GB (AIFF), Astell& Kern AK100 modified by Red Wine Audio, Cambridge Audio iD100, Pro-Ject Dock Box S Digital, Pure i20, Questyle QP1R
Preamplifier: Nagra Jazz, Esoteric C-03, Vinnie Rossi LIO (AVC module), COS Engineering D1, Wyred4Sound STP-SE Stage 2
Power & integrated amplifiers: Pass Labs XA30.8; FirstWatt SIT1, F5, F6, F7; Crayon Audio CFA-1.2; Goldmund Job 225; Aura Note Premier; Wyred4Sound mINT; Linnenberg Allegro monos; Nord Acoustics One SE UP NC500MB
Loudspeakers: Albedo Audio Aptica; EnigmAcoustics Mythology 1; soundkaos Wave 40; Boenicke Audio W5se; Zu Audio Druid V & Submission; German Physiks HRS-120; Eversound Essence; Albedo Audio Amira [on review]; Ecobox Daydream [on review]
Headphones: Final Sonorous X, HifiMan HE-1000 & Susvara, Sennheiser HD800, Audeze LCD-XC, Meze 99 Neo
Cables: Complete loom of Zu Event; KingRex uArt, Zu and LightHarmonic LightSpeed double-header USB cables; Tombo Trøn S/PDIF; van den Hul AES/EBU; AudioQuest Diamond glass-fibre Toslink; Black Cat Cable redlevel Lupo
Power delivery: Vibex Granada/Alhambra on all components, 5m cords to amp/s + sub
Equipment rack: Artesania Audio Exoteryc double-wide 3-tier with optional glass shelves, Exoteryc Krion and glass amp stands [on loan]
Sundry accessories: Acoustic System resonators
Room: Rectangular 5.5 x 15m open floor plan with two-storey gabled ceiling, wood-sleeved steel trusses and stone-over-concrete flooring
Review component retail: €1'295 [incl. 21% VAT]


Metrumome. True or false? With perfect timing like a metronome, Holland's industrial refinery plant of non-oversampling R2R DACs with proprietary silicon keeps knocking out new models. Aside from 'industrial', all true. Cees Ruijtenberg's engineering house is in the process of growing semi-precious stones. First up is Amethyst, to be followed shortly by Onyx and Jade*. For Cees, presenting intel on Amethyst would be "a difficult exercise. I am a no-nonsense guy more focused on getting real results than playing marketing tricks. After all, this couldn't be a terribly exciting tech project when it follows up our older Musette. However, we found that using the DAC Two module meant we had to improve the layout of the Musette board. As you know, our DAC Two with its two R2R ladders runs a very fast FPGA at 400MHz. The ladders themselves can create a 10MHz sine wave in parallel mode but on the board will be limited to the serial formats I²S or RJ24. Interesting is how a single DAC Two per channel compares to the big brothers Pavane and Adagio.

"That's because doubling up converters won't double sound quality. It produces smaller gains. So we think that Amethyst offers a very high price/performance ratio. The next advantage is the use of a quite heavy power supply (30VA + 44'000µF) to add a headphone amp which must drive 16Ω. Without headphones, this extra power is available to the DAC. To create more headroom, both the DACs and headphone amp run on twice the voltage than the Musette did. This also boosted the converters to top specs like the Adagio; and improved their linearity. As a result, you can drive 'phones with a max voltage of 4 volts. This would be quite dangerous to your ears unless the loads were seriously inefficient."


* "The fully balanced Onyx will replace the Menuet with 4 x DAC Two modules plus remote. The Jade will become the poor man's Adagio. Like the Onyx, it will use a quad of DAC Two modules in balanced mode, then borrow the volume tech and 4-knob remote from the Adagio. From a user perspective, it will be completely equal except for the -10dB setting on the rear panel. Form factors will be more or less equal to Amethyst."


Assuming that Amethyst volume control would be conventional not Cees' trick variable reference voltage for the resistor ladders, "correct. In the Adagio, the DACs run with three times higher reference voltage (+10dB). I could have done the same again but with very sensitive headphones, there'd be the risk of some noise. To avoid this, we opted for the classic approach." By design, headphone or amplifier drive omits a traditional output stage. Metrum's in-house designed converters output sufficient voltage to decommission an extra voltage gain stage.


As an entry-level model, Amethyst's case work makes do without the range toppers' glass lid and massive sides. Still, a freshly contoured fascia with deeply inset volume controller adds visual pizzazz and black or silver finishing remain a buyer's choice. "For headphones, there is an impedance down-conversion buffer between the 100Ω Transient modules and the 6.3mm port to arrive at an output impedance of 3Ω."

Amethyst motherboard. "On the right of the two Transient modules you will find an insertion point for future options optimized for even higher data rates."