Reviewer: Srajan Ebaen, Frederic Beudot & John Darko
Financial Interests: click here
Source: 27" iMac with 3.4GHz quad-core Intel Core i7, 16GB 1.333MHz RAM, 2TB hard disc, 256GB SSD drive, ADM Radeon
HD 6970M with 2GB of GDDR5 memory, OSX 10.8.2, PureMusic 1.88a in hybrid memory play with pre-allocated RAM and
AIFF files up to 24/192; Audirvana 1.4.1, April Music Eximus DP1, Esoteric/APL Hifi UX1/NWO-M w. Bakoon BPS-02 battery-
powered Audiophilleo 2, Apple iPod Classic 160GB/AIFF, Cambridge Audio iD100
Preamp/Integrated: ModWright LS-100 with Psvane tubes, Esoteric C-03, Bent Audio Tap-X, TruLife Audio Athena, Bakoon
Amplifier : First Watt SIT1, FirstWatt SIT2, ModWright KWA100SE
Speakers : Aries Cerat Gladius, Boenicke Audio B10, Voxativ Ampeggio
Headphone amp : Bakoon AMP-11R
Headphones : ALO Audio-recabled Audeze LCD2, Sennheiser HD800, Beyerdynamic T1 and T5p, AKG K-702; HifiMan HE500
Cables: Complete loom of Zu Audio Event, KingRex uArt USB cable with Bakoon BPS-02
Stands: Artesania Esoteric double-wide 3-tier with TT glass shelf, Rajasthani solid hardwood console for amps
Powerline conditioning: GigaWatt PF2 on amps,GigaWatt PC-3 SE Evo on front-end components
Sundry accessories: Extensive use of Acoustic System Resonators, noise filters and phase inverters
Room size: 5m x 11.5m W x D, 2.6m ceiling with exposed wooden cross beams every 60cm, plaster over brick walls,
suspended wood floor with Tatami-type throw rugs. The listening space opens into the second storey via a staircase and the
kitchen/dining room are behind the main listening chair. The latter is thus positioned in the middle of this open floor plan without
the usual nearby back wall.
Review Component Retail: €2.185 for the base version, €168/ea. for USB, AES/EBU and extended range output transformers
09 November 2012 18:53. "I intended to email you many times before. But due to our move to Maarsbergen and starting production of the Hex DAC, I failed
just as often. For us the last few months have been a truly crazy mix of moving to the new location and rolling out first Hex units. Our pre-announcement
created massive buzz and preorders. This happened before the production line and measurement facilities were ready. I'd simply never expected this many
early adopters for a brand-new model without a single review.
With this move my own office now occupies the same building as the production plant. Due to our working relationship going back nearly 12 years, we've
decided to cooperate far more closely from now on. This led to the formation of a new entity called All Engineering, a limited liability company which presents
me with the necessary freedom to focus on my job as electronics designer. Daily sales support and technical backup services can be handled by as many
people as are required. Depending on production schedules this could involve from 10 to 15 folks sharing logistics, production and purchasing tasks. I never
anticipated such growth over such a short period of time.
Since the sales figures for the Octave, Hex and various OEM commitments have increased so rapidly, we've embedded a new measurement system in the
production chain to verify our circuit boards at already a very early stage. This means that during build-up to finished product the electronics
passthree different testing cycles which repeat the same measurements on frequency response, jitter, linearity and distortion. I'm really very pleased that the
quality and reliability of our product has now reached such a high level.
I intend to send you a Hex for review but we still have a small gap whereby outgoing orders continue to outpace the rate of incoming parts required for
production. I'll get you a sample in a few weeks." - Met vriendelijke groet, Cees Ruijtenberg
Ruijtenberg's Metrum Acoustics Octave NOS DAC had ceesed its day with quite a bang. In the wake of my Blue Moon award-winning review —recommended
reading for the full background—hifi critics like Martin Colloms had found it just as tasty. Forum feedback from owners added waves. Those soon created a
small giant killer reputation. Predictable if unsuccessful were speculations about the identity of Metrum's industrial R-2R chips. We're told that they aren't from
any of the usual hifi catalogues by AKM, Crystal, Texas Instruments, Wolfson, Sabre & Co but handle data rates up to 15MHz and output sufficient voltage at
sufficiently low impedance to require neither a traditional analog output stage nor I/V conversion. [You might decide that the chips look like TI DAC8580 but
even if they were, without Cees' glue logic you'd not get them to work properly.
With the latest Hex model, Cees' proven multi-parallel scheme for increased signal voltage and lower noise has gone to16 chips. In that it perfectly mirrors
Scott Barry's £6.970 Computer Audio Design 1543 DAC which relies on vintage Philips TDA1543 silicon instead. The fully dual-differential Hex runs eight of
its mystery DACs per channel. Over the minimalist Octave that ran four it then adds Lundahl mu-metal core LL1527XL output transformers, costlier parts and
more extensive socketry. The latter breaks down as BNC, coax and twin optical inputs, RCA and XLR outputs and optional Cypress Semiconductor
asynchronous USB and AES/EBU digital modules.
Cees' 6-layer boards enjoy full galvanic isolation and his 45VA power supply runs three toroids and 18 voltage regulators to separate the conversion circuitry,
control logic and USB. Even though the Hex remains a non-oversampling converter, it handles full 24/192 signal on all inputs expect Toslink (24/96). Output
voltage is a standard 2Vrms for RCA and twice that for XLR. Slew rate is 35VµS and jitter reportedly remains below 35ps. The upper response limit is 20kHz
for 44.1kHz, 65kHz for 192kHz signal. Noise is down a full 130dB relative to a 2Vrms output. Output impedance is 40Ω on RCA, twice that on XLR.
Dimensions are a 320mm footprint with 85mm height. Weight is 5.5kg.
Perhaps like gun-slinging comic-book namesake Jonah this Hex plays it basic on cosmetics. That focuses it on fast drawing performance over sex appeal
which can get old quickly once in the rack. Our Dutch designer's professional roots, bless his heart, still hadn't been usurped by high-end audio's relentless
fascination with excess.
With reduced wallet cramps, the Metrum Hex joins the ranks of posh NOS converters from 47lab, Zanden, Abbingdon Music Research, CAD, Audio Note
UK, Vertex AQ and Concert Fidelity. Here it goes deliberately retro against machines like AURALiC's Vega which upsamples all incoming data to 1.5MHz/32-
bit. Modern Sigma-Delta converters can exploit so-called apodizing filters to eliminate the pre-ringing otherwise endemic to their approach. NOS DACs don't
suffer that behavior in the first place. If they omit digital filters, they do however retaliate with aliasing noise above half the sampling frequency (22.05kHz for
To paraphrase Russell Crowe's master and commander, there's much debate over which of the two is the lesser weevil, ringing or ultrasonic distortion. Here
one mustn't forget recorded pre-ringing from anti-aliasing filters employed during mastering—which NOS DACs of course can't remove though they don't add
to it either—nor this approach's slight treble roll-off. In the end we'll leave the theoretical pros and cons to the engineers both armchair and real and get on
with shamelessly subjective listening impressions.
But first a few final spells on how to work this hex: "For USB we use a modified OEM M2Tech hiFace 1 for a few reasons. In the past we had several
complains of matching an XMOS device to either Mac or PC. From our point of view it thus was too early to implement such a module in our machine. On
several occasions we asked people to return their USB interface and Octave DAC only to find that both were running satisfactorily on our own Mac and
Windows systems. I am certain that the XMOS device wasn't to blame but rather setup problems on specific computers since I couldn't replicate these issues
to establish true cause from the distance. That said, complaints about the original hiFace on either Windows or Mac machines after installing the proper
hiFace driver have been exactly nil.
But using this OEM module as a quasi hiFace wasn't our goal. Marco Manunta relies on USB power. This can readily cause all kinds of issues by injecting HF
noise into the DAC or forming ground loops which can pick up airborne frequencies from domestic equipment. So we disconnect USB power and feed the
OEM module with our 15VA linear power supply which also has complete galvanic isolation from other parts of the Hex. As the data output from the OEM
module is useless to the actual data format of our DAC, we add our glue-logic circuit for data 'translation' and buffering which fits below the USB module on
the distribution board
Before settling on this particular OEM module over competitors we also verified its digital transparency by feeding it well-known bit patterns from our analyzer.
By measuring this pattern once it exited the OEM module we could ascertain that it indeed operated bit perfect. This became another reason to use it. The
USB module is optional so people can use their own USB bridge if preferred. From a marketing perspective there's another reason to make it optional. We
see two types of customers who might purchase our Hex DAC.
"1/ Music-loving hobbyists. They like to set up a computer as music server and spend much time tweaking it. They need a USB input to run their system. We
think this audience makes up about 5%-10% of our total market.
2/ Music lovers. They spend money but aren't inter