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Conductor/Aurix. With the Dutch connected to the Australian's fixed out, A/Bs just mandated a reseated ¼" plug. With Aurix I had to wait a few seconds before its output relays opened the gates. Again active action and passive purity juxtaposed. Fistfuls of left-handed piano chords, upright bass exploits from Garcia-Fons, the three-stringed Moroccan gimbri bass of the Hadouk Trio's popping and pounding Loy Ehrlich, Anna Lechner's elegiac cello and the Hans Zimmer-style albeit African drums on Jamshied Sharifi's quasi soundtracks all had greater wallop with the Conductor. This bottom-up reading was more massive and locomotive. By contrast Aurix wiped out what seemed minor fuzz or blur. Tremolos showed more on-string action. Chinese erhu exhibited more of its peculiar harmonic frisson. Latin Salsa brass had more bite, cymbal workouts more sparkle.

The rise of struck triangles, Andy Narell's hollow steel drums, the clacks of wood blocks, the zing of xylophones, the rapid arpeggios of Rafael Cortés' guitar on Cagiñí and the coruscated cymbalom clatter on Angelo Debarre's Jazz Manouche all showed more quicksilvery reflexes. This leaner cleaner fashion benefited separation whenever the going got convoluted. Since Burson's voicing has always favored the meatier chunkier aspects like a Zu speaker where the price to pay might be minor opacity, I thought the combination of Conductor DAC + Aurix headphone 'converter' most successful. Because the powerful Conductor is a drive-anything machine, I went straight to the HifiMan HE-6 to challenge the Dutch.

Using the subdued opener of a Bratsch cut to come in well below dynamically compressed fare which essentially redlines constantly just below clipping, my ears' loudness meter wanted 2 o'clock on the Conductor. In no-gain mode this meant that the Alps pot of the Aurix was fully bypassed. For my needs the extra 10dB headroom of the transformers remained untapped. I reckon that for most with bog-standard 2Vrms sources, Aurix would be sufficiently loud even into Fang Bian's most inefficient planar. From my collection of cans this meant that everything else was a go too. Hence I thought that Cees' math on gain and application-specific voltage swing had called our headfi needs just right. I cannot of course know what the indestructible i.e. immortal hearing of adolescent ravers would say about that. They simply wouldn't own HE-6 but Beats.

HifiMan HE-6 with stock cable.

It's sobering to think—and perhaps a worthy cost-effective DIY project to pursue—that a simple buffered volume control could compete so well against very serious active circuits which are executed fully discrete to avoid op amps and IC regulators. Particularly if you had an innately lush warmish slightly dark 'phone like an original Audeze or the Alpha Dog version, the <€1'000 Aurix could be nearly ideal. To get what it does plus the elements of active drive (and versus its passive purity not active's mild filter effects) should require a Bakoon. That would up the game to ~€2'000 for their new HPA-01 and thus play in the twice-as-much league. Obviously here source quality is the primary sonic determinant. You can't expect flavor transformations from a passive.

What you can expect is a close-up look at the often far more subtle differences between software players, in my case PureMusic 1.89g R3 vs. Audirvana 1.5.12. The same holds for flavor layers between decks which otherwise perform on the level like a Vega, Hex, Clones Audio Sheva or Wyred4Sound DAC2se. The greater complexity of speaker-based systems with their added cables, crossovers and room interactions obscures or minimizes these differences. With good headphones and as simple a circuit as the Aurix, these difference become more pronounced. It might not make them easier to describe but it certainly makes them easier and more important to hear - and thus either to pursue or pass on.

Doing a quick tour with Alden Zhao's CMA800R Questyle revisited an earlier remark. Despite its responsive litheness and quickness, the treble of the Aurix doesn't get thin, pinched or strident. The Chinese deck played it sharper, spicier, more forward and on edge. Somehow its active drive, current gain and hyper bandwidth combine into a top end that's very lit-up and in charge. This also makes the multiplicity of mass detail more intense. The Aurix handles these aspects more limpid if you will. Clarity without showiness or extra brilliance. My existing take on Hex and Vega aromas and their narrower parallels between PureMusic and Audirvana tracked clearly. From these options I'd go for Vega + Audirvana to increase textural wetness, color intensity and minor sweetness. This would counter steer a bit. The Hex + PureMusic front end into the Aurix acted more alike. In either case and to reinvoke the toons, it never behaved like Cacophonix. It evoked what the Germans call this slight Albert Uderzo character. Troubadix. This chap doesn't blow a horn or pound the drums. He plucks a lyra to be light, quick, clear and harmonious. But he's not a strongman like the Gauls' chief characters. This means that the bass foundation is lighter, the stage less anchored in infrasonics and tonal black values aren't as inky and deeply saturated as proper active circuits can be.

On raw SPL Aurix got it up into all of my loads. On max performance relative to prior sightings with competing amps, I'd eliminate the HE-6 and AKG's K-702 from my bunch. Those sound grippier, more robust and involving over the Conductor or L1. Sennheiser's HD800 and beyerdynamic's T1, HifiMan's HE-500 and my Audeze LCD-2 as well as MrSpeakers' rebuilt Fostex planars were my top picks for the small Dutch amp. Considering how most headphone amps of recent acquaintance were rather costlier, I thought going Dutch was surprisingly effective and into the right loads just as valid. Like the Octave MkII DAC it's been styled to match, Aurix probably isn't Ruijtenberg's ultimate statement on the subject. He'd probably spend a chunk more on his headfi Hex. But like the non-oversampling Octave with on-chip I/V conversion and no conventional output stage but a very solid power supply, Aurix demonstrates how proper engineering guided by clearly good ears can cut right through the crap and deliver advanced sonics with minimal fuss: purist circuitry without any of the hair-shirt wonkiness which can sometimes accompany the minimalist approach. Here it simply means starting with the best source you can muster, then 'direct-coupling' to it this properly buffered volume control which terminates in a ¼" jack and adds an optional 10dB of passive voltage gain (which you're rather unlikely to need particularly off a 4V or higher modern DAC).
Metrum Acoustics comments:
It seems your findings exactly parallel our statement on the absence of coloration and the increased ability to hear the properties of several components in the signal chain. As a matter of fact this gave us more ideas for using this technique to avoid masking interesting musical details. It could do a good job in the output sections of converters and preamps. It also brings me to new techniques we are investigating presently as we're convinced that information buried in the noise floor remains relevant. I've attached a lab experiment. It shows a 1kHz stimulus of -135dB (related to 2Vrms) coming from a prototype DAC. On the left side you can see the 50Hz hum which is already very low and probably picked up from my soldering iron. In the middle you see this stimulus and the 2nd harmonic around -145dB at 2kHz. Assuming that we can hear such small details in the noise we have to assure that they won't be masked by the electronics to lead to this type approach. This low noise floor of about -153dB helps a lot but has forced us to go deeper and deeper. Our transformer solution is one of the ways to recover such very weak information.
Cees Ruijtenberg

Metrum Acoustics website