In today’s marketplace, Metrum Acoustics is the most prominent of Dutch outfit All Engineering’s brands. They have experience in the field of audio dating back to 1989 and while then it was electrostatic technology that spread their brand name, they are still pushing forward with innovation. The only difference is now they have a focus on electronics, even more specifically their non-oversampling digital circuits, which it is known I am a huge fan of. While it is certainly DACs that I would always associate Metrum with, they also carry some amplification to provide an analog compatriot to their digital offerings. It is actually one of their amps I will be reviewing today although it is hardly a brand-new release. The Aurix is a headphone amp that was made to be used with the now discontinued Octave MKII DAC. It hit the stores back in 2014 but outside a very in depth article from 6moons, it slipped under the radar a bit.
I think with the headphone market being much younger than your traditional 2 channel systems, the more basic approach from Metrum may have held them back a bit. Their website is dated and while English is not their native tongue, typos on their website were noticeable. On top of that, it is just a very boring looking product. It is your typical conventional looking amp with no flare. Being single ended top to bottom also discriminates against the majority of high-end headphone users that look for one of the excessive amounts of balanced connectors, my preference is dual 3 PIN XLR, I know Sennheiser just implemented the 4.4mm jack. All of this is very much external and I am sure your mother always told you, it’s whats on the inside that counts, that is very much the case with this product. It is tagged with an RRP of €995 but Aurix is currently on offer for €595, a pretty hefty discount if you ask me. This discount is very recent and actually a further €200 reduced to what it already was. Perhaps this is its new fixed price?
Taking a Look Under the Hood
Metrum has gone into headphone amplification with a fresh and unique mindset. It is a very simplistic approach where they use a step-up transformer as the source for gain, which I shouldn’t have to tell you is very much against the norm, in fact very far from it. To support the transformer they have two FET transistors, one either side. One is an impedance converter for the transformer, a role it is suited for having a high bandwidth and the second one is used to actually drive the headphones. That is the complete signal path, sitting in a valley of heat shrinks to give an outlet to the heat Class A circuitry produces. Everything else you will see inside the amp is to set the environment and to create the most seamless operation. The only clicks I get are when selecting the input switch and that is followed by a more brief delay of 5 seconds before we hear melodies make their way to your ears. Apparently, 60% of the circuit board is dedicated to the protection, while a good thing it is something I expect in opposed to wanting to scream and shout about.
As I know people like to look at some different numbers I asked head designer Cees Ruijtenberg a little more about the output.
“Output impedance is around 3 Ohms. Max Voltage is 6 volts RMS in high gain.
32 Ohms will give a maximum of 1.1 WPC with 6 Volts RMS but it is not logical in case of high-efficiency cans. In such cases, the low gain setting is max 2 Volt RMS using a DAC with redbook standard. So in case of 2 Volts, your max power is 0.125 Watt but will create ear bleeding levels.”
I have predominately used Aurix with my flagship headphones which tend to be a little harder to drive. I am talking Sennheiser HD800, Mr Speakers Ether Flow and even the slightly lower impedance Focal Elear. These all preferred the more powerful high gain mode that adds 10dB to the mix. Cees is right, you don’t need the behemoth amounts of voltage or watts to get headphones loud in almost all cases, but taking control over the driver and bringing the best out of it is a little more of a challenge. The bottom line is that we can establish this amp can offer some decent power if necessary! The Ether was handled much better than the ZMF Blackwood of the two I tried. I still found the low gain mode exceptionally handy, especially with my efficient headphones such as the Ultrasone Ed10 and Beyerdynamic T5p that I still like to use from time to time, especially the latter when my family are being noisy. Even IEMs are an option should you deem it necessary. I plugged Campfire’s Andromeda into them and got the same sort of hiss as something like the Cayin i5 DAP so that is pretty good going.
While I hate it when it happens, I am surprised Metrum didn’t make this an all in one unit, with digital inputs ending up in a quarter inch headphone jack. It is certainly the ‘in’ thing to do at the moment, maybe this was released just before that trend. The more likely reason was that this was made to compliment one of their existing DACs, not replace it. While being optimised for the single ended Octave MKII, Metrum should be aware that many users would already have a DAC and I think it is a shame that at this price it lacks balanced operation. On top of the power and gain switches, we have 3 pairs of RCAs on the back, two as inputs and one as an output. The output means you could have this passing through into a stereo amp should you wish. The front panel, the only part silver on a black body (a black faceplate is an option), hosts a small but rather protruding volume pot flanked by an input switcher and single quarter inch jack. No sharing your music with this….
It is funny because shortly after writing the above paragraph Metrum announced the Amethyst, a new entry level all in one unit that is indeed both a DAC and headphone amp. It looks like they subconsciously read what I had written. Amethyst will retail for €1,295.
While it doesn’t have any flaws in its aesthetic is has no talking points. It lacks the perfect finish of my Questyle’s, the wooden case of our Ear 909 or even the buttery knob feel of Simaudio’s 430HA. It is functional with everything labelled correctly and I can appreciate where Metrums priorities lie. More problematic for me though, was the actual build quality. My unit for no apparent reason never rests on all four feet. The back left piece of rubber is always slightly elevated, which both bugs my OCD and can’t be optimal for sonics. While not actually an issue I also find the chassis to be on thinner side, prompting a rattle when tapped.
When it comes to a product like Aurix, I think its design really does put pressure on how it sounds. It needs to be landing a knockout punch because I don’t think it is going to have the appeal elsewhere. Maybe you like this more basic looks and if you are running it with a Metrum DAC the aesthetics maybe compliment each other at the very least.
More on the next page….