I know I’m a sucker for the Metrum DAC sound, but I had other primary reasons for trying out the Aurix. Impressions or reviews are pretty lacking for this amp, but I noticed it shared some design choices with another amp that I quite liked, the ECP Black Diamond prototype. Both utilize step-up transformers, and both use no feedback. Beyond that, I’m not sure how similar the designs and implementations are. What reviews and impressions I could find didn’t always seem to line up perfectly with each other. The 6Moons review suggested the Aurix was more about digital speed and clarity of sorts, and a couple Head-Fi user impressions suggested it was rather smooth and easy to listen to with the HD800. Ah, well, I figured I’d give it a shot either way to see if I might be able to capture some of that Black Diamond goodness at less than half the price (HiFiHeaven had it for $700 on eBay).

Specifications for the Aurix suggest it performs better with higher impedance loads, with 0.01% THD max for a 600 ohm load and 0.5% THD max for a 32 ohm load. Output impedance is 3 ohms, though I don’t believe the site lists this. In my experience, the Aurix doesn’t work very well with most orthos. Something like the PM-1/2 works well enough on it, though even it will sound a tiny bit less powerful than when run from a more powerful amp. Less sensitive orthos tend to just sound a bit more strained on the Aurix. Even then, I don’t believe I hear any audible degradation of the sound on lower impedance headphones due to the relatively high THD (could be wrong). The HD650 seems to run well from the Aurix and has plenty of headroom to play with. Generally I run the gain at the +10dB setting. It's a bit sweeter sounding than 0dB...just a bit.

Most of my impressions will use the Leckerton UHA-6S Mk.II (w/ ADA4627-1B opamps) for comparison. I know the Leck isn’t necessarily a top-tier amp, but it’s well received, and many on this site are familiar with it.

It’s been a while since I’ve heard the Black Diamond, but there’s definitely one quality it and the Aurix seem to share. I’ve heard many say the BD has a more intimate soundstage and presentation. Tighter-knit, but fleshed out, if you will. The Aurix seems to share that same trait. There’s less of a sense of room or venue space and reverberation compared to other amps. Sometimes things can get a bit crowded sounding, but rarely in a way that necessarily covers up elements or details. You may in very particular scenarios have to listen a bit closer to pull out some things in a complex mix. The lack of relative air and reverberation on the Aurix can make some elements of the music sound like they stop too short or were damped more in a way. But, generally, separation is not bad, and where there may be a lacking sense of air or reverberation, it makes up for it by sounding very focused and well-defined. The Aurix seems to have a decently black background and has no detectable noise or hiss.

This sense of focus and a tight-knit, fleshed out sound seems to give everything a nice sense of texture and palpability. Think "rich" or "lush" without the connotations of warmth or thickness that most might be thinking of with those words. Vocals sound less ethereal, less likely to sound distant, or sound too blended with everything else. They’re more full-bodied and crisper on the Aurix and may have a better sense of harmonics. Vocals just sound more real to me on the Aurix. On tracks with many layered vocals, while there is less of a sense of ambiance behind the combined voices, each voice sounds like it is better defined internally and can often be easier to pick out despite the smaller sounding soundstage.

Many other elements of the music get that sense of being fleshed out and very textured. There is an additional sense of “inner-detail.” Fleshed out, crisp, and quick without being too hard or sharp. However, there’s a downside to this. Sometimes this text uring can come across as a bit rough and a bit too forward or aggressive. This seems to be primarily centered around the upper-mids and lower-treble, depending on where you define those areas in terms of frequency.

I remember, perhaps incorrectly, the BD prototype being a bit smoother and more relaxed in this regard, but perhaps it was also susceptible to this: http://www.changstar.com/index.php/topic,818.msg52256.html#msg52256

The Leck certainly sounds more easy going in this regard. Smoother, but also sometimes not quite as textured or resolving in these areas (though I suppose the Aurix could have a false sense of texture and resolution...not the best guy to answer that). Of course, the Leck has a less intimate, more pushed back presentation in comparison, and that also factors into this. It’s just less forward about it.

On the other hand, with the HD650, the Leck seemed to have a slightly grainier and more lit-up top end. So while the Aurix is more relatively forward and sometimes less pleasing in the mids through low treble, the Leck is more forward and sometimes less pleasing in comparison when you go beyond that point. In general, both seem to be relatively decent at resolving details…I didn’t detect huge differences when it comes to resolution beyond the areas I specifically touched on. The Aurix might sound a bit faster overall, maybe. Though, I suppose the Aurix was a bit less defined sounding in the low bass on certain material. It certainly seems to have a better grip and maybe even more power when running the HD650 vs something like the PM-2 (i.e. it started to bridge the gap with the Leck in terms of what I mention in the next paragraph).

The Aurix has a touch more warmth in the lower mids and upper bass compared to the Leck. The Leck has more power, emphasis, and thickness below the low-mid point. It sounds thicker, a bit more powerful, and has a bit more kick on the lowest registers than the Aurix. If memory serves me correctly, the Black Diamond may have been warmer sounding than the Aurix. I do remember the BD having a softer bottom end, and the Aurix seems to also fall into that camp. They’re probably more similar to each other in this way than either would be compared to the Leck, but the Aurix overall doesn’t sound quite as soft in the low and high registers compared to the prototype BD. Again, this is all based off memory, so take that with a grain of salt.

I’ve heard claims, some from Metrum Acoustics itself, I believe, that the Aurix is supposed to be relatively transparent and is more likely to reflect what you feed it. As such, maybe, just maybe, it’s more sensitive to various power cords, interconnects, and sources than the Leck and some other amps. Maybe not. That’s not something I’ve had time to play around with to say one way or the other. I’m also not the best guy to be judging how transparent or revealing an amp really is anyway, but I hope to experiment a bit more with everything in the chain driving the Aurix. It’s an area I need more exposure to. If anyone else here has heard this amp and has thoughts, I'd love to hear them to get a better reference point on how this amp might compare to others I have not heard ('cause I haven't heard a ton of amps).

Anyway, overall I feel fairly positive about the Aurix. It’s not quite as easy-going as I remember the Black Diamond prototype being, but my memory could be poor, I don’t have the same source equipment this time around, and the headphones are different too. It’s more of a guessing game at this point, trying to compare the Aurix to the BD. It’s probably more similar to the BD than the Leck overall, though. What draws me in is how textured, focused, and fleshed-out the sound can be at times. That can be very engaging and addicting. What makes me unsure I’ll keep it forever is that this same element can also sometimes be too much, and the intimate pre sentation is more likely to set me on edge (good or bad). But, like I said, I still have some experiments to do with it to see if maybe any “issues” I have with it are more due to what I’m feeding it. If I notice any changes, I'll be sure to post them. One aspect I’m curious of is how well it truly works with the HD800 if some of you folks were to try that combo, because it seems the few people that do have an Aurix use it with that HP. Maybe I can put it on a loaner tour…

One other thing to note is that this amp needs to be warmed up to sound its best, by at least 30 mins if not a full 24 hours. I do believe it opens up with burn-in, so I ran about 100 hours on it.