Metrum Acoustics Aurix

Frustrating lack of impressions/reviews for this, I guess they are pretty uncommon?  I'd love to know more.

I may have to take one for the team and buy it, just to hear how a Metrum stack shapes up 

My Aurix is here and burning in. Will post impressions soon.

It's been 4mn already!

clemmaster said:

  It's been 4mn already!

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Well - all I'm going to say for now is it is very transparent, very clean, and the LCD-X sounds much better than it has been out of the Hugo.  Far more resolving than the Violectric V200 and far less coloured (out of the Octave Mk1).  Liking what I'm hearing a lot.
 
PS Always a good sign when you don't want to take your headphones off.  Itunes on random - a track from John Tavener's the Myrrh Bearer came up - goosebumps. Great acoustic, great dynamics.

That is promising
Keep it coming, please!

Still burning in, but I certainly already feel that I had never heard the Octave at its true potential until I bought this amp.  Detail, amazing acoustic, no digital glare.  

What about dynamics?
6moons review seems to imply it is quite laid back.

Dynamic range is excellent. It is laid back only in the sense that the detail is not "in your face", but presented in a flowing, musical fashion.

I'm loving this combination with LCD-X, which I found too strident out of my Hugo.  There is something so effortless about the presentation, it has that distinctive Metrum tone but is not "dark" or "thick" - the Aurix keeps everything clean and tightly focussed.  The detail is there, but it is definitely a sound to relax into and get lost in, rather than to be pummelled into submission.

Are you using it with the Octave mkII?

No Sir, the Mark 1.  

3rdmortal said:

  I`ve listened to Metrum Octave + Aurix recently with my 990 Pro. And it was gorgeous! Even if 990 Pro is not a top notch. I know ... The sound was very smooth, dynamic and emotional. Aurix compared to other less expensive amps represents middle frequencies in the best way possible. The sound is not thin but thick and very sweet. No sibilants at all. Everything is so clear and each note is so precise. I liked it more than lehmann black cube, spl auditor, meier concerto, v200 and so on. Metrum is a really unique company indeed.      

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pjotr27 said:

A few weeks ago i buy this amp. First right out of the box , not convinced. But after playing a lots of hours, sound is wonderful. Together with my Ath-w1000x grandioso its a very highend combi and i never heard better sound through phones. If you had the opportunity to listen to a well burned Aurix, do it. It will surprise you!

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tokengesture said:

 

 
Well - all I'm going to say for now is it is very transparent, very clean, and the LCD-X sounds much better than it has been out of the Hugo.  Far more resolving than the Violectric V200 and far less coloured (out of the Octave Mk1).  Liking what I'm hearing a lot.
 
PS Always a good sign when you don't want to take your headphones off.  Itunes on random - a track from John Tavener's the Myrrh Bearer came up - goosebumps. Great acoustic, great dynamics.

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tokengesture said:

  Still burning in, but I certainly already feel that I had never heard the Octave at its true potential until I bought this amp.  Detail, amazing acoustic, no digital glare.  

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tokengesture said:

  I'm loving this combination with LCD-X, which I found too strident out of my Hugo.  There is something so effortless about the presentation, it has that distinctive Metrum tone but is not "dark" or "thick" - the Aurix keeps everything clean and tightly focussed.  The detail is there, but it is definitely a sound to relax into and get lost in, rather than to be pummelled into submission.

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Your testimonies are all very compelling!
 
I've only had the Metrum Octave MkII for a few days but I'm really enjoying the NOS sound - there is a lifelike palpability to the instruments and voices that I've never heard with any OS DAC - a conspicuous absence of sterility, of which I was previously unaware with all of the ESS9023, ESS9018, and CEntrance DACs I've owned. They sound plastic now that I've spent many hours with the Octave MkII.
 
In emails exchanged with Cees Ruijtenberg, who by the way, has not even once mentioned that he sells a headphone amp, he has told me that the remaining brittleness I hear in my HD800 can be helped by (replacing my OPPO HA-1 with) a zero-feedback or low-feedback amp. 
 
I've recently uncovered a lot of great information about the role of applying negative feedback in amplifier design - especially as needed with multiple gain stages, but an article by Nelson Pass has convinced me that there's a problem of diminishing returns where the more dB of negative feedback that's applied, the more complex becomes the remaining distortion, even though you've managed to suppress it greatly.  And worse, the harmonics suffered naturally in the absence of applying negative feedback (best tolerated with a single gain stage), can actually be desirable, making the music sound much more realistic than it would with those harmonics suppressed.  It might even have measurably bad distortion, but from the perspective of just listening to the music, it can be preferable to suffering the complexity of distortions that occur (albeit at low levels) when lots of negative feedback is applied - a complexity that ruins the naturalness of the sound.
 
Cees Ruijtenberg is all about taking a minimalist approach - not processing the signal. The Aurix uses only two transformers for gain - no transistors or tubes in the signal path!
 
Quoting the 6moons review of the Aurix, did anybody notice this?:
 

 The FirstWatt M2 and F6 power amps use small transformers for passive gain.

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Cees Ruijtenberg apparently thinks much like Nelson Pass when it comes to amplifier design. 
 
No local or global feedback is applied in the Aurix.  I'm convinced (by the writings of Cees Ruijtenberg and Nelson Pass, primarily) that the HD800's unparalleled resolution makes it less tolerant than most headphones of the complexity of distortions that can be heard in low level signals with amps that employ negative feedback. And it's those low level signals that contain a wealth of "data" our brains can process to discern the original timbre of instruments, the trailing edges of their decays, the natural echos and micro-details that define the recording space, etc.
 
Here's the Nelson Pass article I found on the use of negative feedback:
 
https://passlabs.com/articles/audio-distortion-and-feedback
 
And here are some key excerpts:
 

At one extreme, the position is that “feedback makes amplifiers perfect”. At the other extreme, “feedback is a menacing succubus that sucks the life out of the music, leaving a dried husk, devoid of soul”.

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We use negative feedback in audio amplifiers to stabilize the gain, increase the bandwidth, lower the output impedance and lower the non-linear distortion. It is the aspect of reducing the distortion which tends to generate the most controversy – negative feedback is very successful in lowering distortion to very tiny numbers as measured by distortion analyzers.

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But when two tones are passed through a non-linear device, the amplitude of each of the tones is altered, or modulated by the other tone. The result is a series of “sidebands”, additional tones occurring at the sum and difference of the original frequencies. These additional tones are not generally musically related.

Worse, real music consists of very many tones passing through the nonlinear gain device, and each of these interacts with each of the others. The result will be very complex, and very unmusical.

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Negative feedback is good at reducing all forms of distortion, linear and nonlinear. As a concept, it's pretty straight-forward: You create one of more gain stages in series in order to get enough gain to equal the final gain figure you want plus the amount of feedback you think you want to use.

As the feedback figure exceeds 20 dB or so, you find that all the measurements will improve by the amount of additional feedback. If the open loop distortion of the amplifier is 5%, then 60 dB of feedback should make it about .005%. It's relatively easy to construct additional stages or to milk existing stages for more open loop gain, so why not 80 dB for .0005%?

Sounds like something for nothing, doesn't it?

Not quite. I think it's a bit more like a credit card – convenient if used wisely, but carrying interest payments and penalties when it's not.

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We have seen that nonlinear distortion becomes larger and more complex depending on the nonlinear characteristic of the stages, the number of cascaded stages, and the number of spectral elements in the music.

Negative feedback can reduce the total quantity of distortion, but it adds new components on its own, and tempts the designer to use more cascaded gain stages in search of better numbers, accompanied by greater feedback frequency stability issues.

The resulting complexity creates distortion which is unlike the simple harmonics associated with musical instruments, and we see that these complex waves can gather to create the occasional tsunami of distortion, peaking at values far above those imagined by the distortion specifications.
If you want the peak distortion of the circuit of figure 13 to remain below .1% with a complex signal, then you need to reduce it by a factor of about 3000. 70 dB of feedback would do it, but that does seems like a lot.

By contrast, it appears that if you can make a single stage operate at .01% 2nd harmonic with a single tone without feedback, you could also achieve the .1% peak in the complex IM test.

I like to think the latter would sound better.

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I'm so very tempted to try the Aurix... 
 
Mike
 

More food for thought....
 
Consider the following excerpt from a thesis on the subject of negative feedback use in amplifier design:
 
http://www.dancheever.com/main/cheever_thesis_final.pdf

Quote:

1. Introduction

In September on 1995, Stereophile, an established highly respected hi-fi magazine, ran a review of the Cary 300SEI, the first mainstream review of a single ended amplifier. In this design, a single output device is tasked with producing both polarities of the signal swing and had zero negative feedback.

Robert Hartley, one of the senior reviewers, states:

"The 300SEI communicated music in a way I’d never experienced before. There was an immediacy and palpability to the sound that was breathtaking- a musical immediacy the riveted my attention to the music. It reproduced massed violins with beauty unmatched by any electronics I’ve had in my system. It excelled in the most important areas: Harmonic rightness, total lack of grain, astonishing transparency, lifelike sound staging, and a palpability that made the instruments and voices exist in the room."

The article then follows with lab bench test results. They were easily the poorest result in every specification; output power, frequency response, output impedance, total harmonic distortion, intermodulation distortion, and cross-talk.

"This amplifier measured so poorly as to be a joke...contrary to what we consider good technical performance. I’m convinced the 300SEI doesn’t harm the signal in ways push-pull amplifiers do, and that what the 300SEI does right is beyond the ability of today’s traditional measurements to quantify. I have become convinced single ended tube amplifiers sound fabulous in spite of their
distortion, not because of it."

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Anyone not familiar with Robert Harley [not "Hartley", as quoted in the Cheever's thesis] should know that he commands a lot of respect in the HiFi community. 

Interesting. I'm not at all technical - I follow my ears, which is tricky when there aren't many meets to get to listen to stuff.  The Metrum combo certainly seems very transparent and life like - it gets out of the way and leaves you listening to the music which is what I'm after in my desktop system.  It also highlights the differences between headphones.
 
The Aurix is well worth an audition if you can, especially if paired with the Octave.
 
PS just plugged in my Earsonics S-EM6 IEMs in them for the first time.  Amazing sound, no noise, stunning.