[beyerdude]

   
I just caught this on a re-read of recent posts...
 
Beyerdude, are you an organist?   I was a student of Lloyd Del Castillo (in Hollywood, in what seems like another life...) when he was inducted into the ATOS Hall of Fame - which means he was stunningly good and I was stunningly bad.  

  On his three-manual Rogers, he only wanted me to practice with his favorites - songs like Cole Porter's Begin the Beguine, but when I'd get home I'd jam to my sheet music instead - mostly R&B. I would beg to play something he didn't like on his Rogers and he would only rarely oblige me out of curiosity, then it was back to his stuff.  He hated me!  LOL
 
I haven't touched an organ in twenty-seven years - when I had to sell my (unimpressive but fun) two-manual, fifteen pedal Kimball spinet, that had a Leslie speaker (Woohoo!) to make way for our first child, turning what had been my music room into a nursery.  Sigh...  Now, my only keyboard is a 1911 Henry upright piano.  (Don't sell your organ - whatever it is!)
 
Mike

Hi Mike - sorry just got round to seeing this - I was thinking more about a kidney - my talent in music amounts to playing the same 4 chords on a guitar that I learnt 30 years ago....

 

[beyerdude]

   
I want to spend more time with the Metrum stack, but one way to summarize it would be to say that the HD800 has been moved in the direction of taking on the virtues of the LCD-2 (bass energy and smooth, fatigue-free treble) without its weaknesses (poor sound stage, lack of treble air and resolution), all the while retaining the virtues of the HD800 (resolution, sound stage, imaging), shedding its weaknesses (brittle treble, lack of bass energy).  Notice the emphasis on "in the direction of"... The HD800 still doesn't have the bass energy of the LCD-2, but more so than on any other chain I can assemble with my gear, but the treble is almost completely fatigue-free.  I say "almost" because Fleetwood Mac's Rumors - an album that has some very challenging treble content for the HD800 - is now tolerable - for the first time ever with the HD800 (vs. being so excruciating I normally use the LCD-2 or PM-1 - any other headphone - for that album). 
 
I'll also add that, so far, I've not found anything to complain about with the Aurix, sonically, but if I wanted to be nit-picky, I wish the chassis was heavier, because removing the headphone plug from the TRS jack requires two hands - one to pull the plug and the other to hold the Aurix down on the table.  

 
Lastly, before I end up writing the review I didn't want to write, the Aurix by itself does not have as dramatic an impact on "fixing" the HD800's problems as does the Octave MkII, but when the Octave MkII and Aurix are used together, as they were intended, they seem to magnify each other's strengths.  For example, the bass comes in more strongly with the Metrum stack driving the HD800 than when using the CEntrance DACmini CX with the Aurix or when using the Octave MkII with the OPPO HA-1 amp.  There really is some kind of synergy at work between the Metrum siblings.
 
NOS DAC + Zero-feedback Amp = HD800 Happiness 
 
More later!
 
Mike

Yep - smooth, relaxing, suits many more genres of music. I am very pleasantly surprised about how good the HD650 sound with it also - the bass has tightened up, overall more definition - very positive improvements indeed. 

 

[zilch0md]

I've been using the OPPO PM-1 with the Metrum stack - this morning - for the first time - for about 5 hours now.  It's efficient enough I've concluded I don't hear anywhere near as much loss of dynamics as I do with the LCD-2 (or even the HD800) when toggling between the Aurix 0 dB and 10 dB gain settings and adjusting the volume control to tape-marked positions established by volume matching with a white noise file and SPL meter.  I do hear better dynamics with the OPPO PM-1 at the 10 dB setting, but it's subtle, leading me to believe that the PM-1 is not quite efficient enough to deliver its best at the 0 dB setting - but nearly so.
 

 
10 dB Gain brings the step-up transformer into the signal path.
 
 

 
Marks on tape show the volume-matched positions for 10 dB (at left) and 0 dB (at right), for a measured 80 dB SPL inside the ear pads of the OPPO PM-1 playing a white noise WAV file. (Imagine those marks moved farther clockwise for the HD800 and more so for the LCD-2.)
 
Both the HD800 and the LCD-2 rev.1 are too inefficient to use the 0 dB gain setting without compromising dynamics, as heard with really dynamic recordings like Beck's Sea Change or Michael Hedges' Aerial Boundaries. The OPPO PM-1 (PM-2), on the other hand, are efficient enough that I can only hear a slight difference in dynamics and no discernible difference in bass control or speed when toggling between 0 dB and 10 dB. This would be the same for the PM-3, also, since it's even more efficient than the PM-1.  The DAC alone might be able to provide enough power for the PM-3 (through the Aurix at 0 dB.)
 
Interestingly, I'm hearing a little more bass energy with the step-up transformer in the signal path than without. This again, is with the Aurix driven by the Octave MkII, where a synergy of some sort yields more bass in the high impedance HD800 than with the low impedance OPPO PM-1. So, although the bass energy is not boosted as much with the OPPO PM-1 as with the HD800, at the 10 dB gain setting, there's a detectable increase in bass energy in the PM-1 with the 10 dB gain setting vs. the 0 dB setting.
 
Still, there's something else happening when the step-up transformer is engaged (10 dB) - more of the euphonic tonal qualities that are so lacking in the HD800, but less needed by the PM-1, and even less so by the LCD-2 - for my tastes. Without the step-up transformer, the PM-1 is able to hear the DAC with little more than the attenuation provided by the volume control and some impedance matching, but if you want an even less "sterile" sound - of which the Octave MkII can hardly be accused, using the step-up transformer of the Aurix will deliver it - I am absolutely certain of this - tube-like goodness resides in the step-up transformer.  I couldn't determine this using my less efficient headphones because they "need" the extra power of the transformer, so 0 dB really isn't an option for them - if you want to maximize their performance overall.
 
In an attempt to quantify this "euphonic" contribution made by the Aurix transformer at 10 dB of gain, I'll say that I'm still convinced the Octave MkII makes a much greater contribution to euphonics, when used with other amps, than does the Aurix when used with other DACs, but the best increase in bass energy seems to come from pairing the Octave MkII with the Aurix while using the transformer, and they are more effective in this regard with high impedance loads than with low impedance.
 
I hope I'm right about all of this stuff.  When I start making really specific "observations" like this I get nervous, because I do feel a burden to be accurate for the sake of others who might act on what I write. Still, I'm saying it as I hear it, so hopefully my findings can be found reliable.
 

 
With that disclaimer, I'll stick my neck out a little farther by adding that the treble energy is rolled off a bit with the transformer in the signal path - great for HD800, OK with the PM-1, but not really desirable with the LCD-2 rev.1's already shelved highs.  It's very slight, however.
 
Mike

 

[knowhatimean]

Quote:

  I've been using the OPPO PM-1 with the Metrum stack - this morning - for the first time - for about 5 hours now.  It's efficient enough I've concluded I don't hear anywhere near as much loss of dynamics as I do with the LCD-2 (or even the HD800) when toggling between the Aurix 0 dB and 10 dB gain settings and adjusting the volume control to tape-marked positions established by volume matching with a white noise file and SPL meter.  I do hear better dynamics with the OPPO PM-1 at the 10 dB setting, but it's subtle, leading me to believe that the PM-1 is not quite efficient enough to deliver its best at the 0 dB setting - but nearly so.
 

 
10 dB Gain brings the step-up transformer into the signal path.
 
 

 
Marks on tape show the volume-matched positions for 10 dB (at left) and 0 dB (at right), for a measured 80 dB SPL inside the ear pads of the OPPO PM-1 playing a white noise WAV file. (Imagine those marks moved farther clockwise for the HD800 and more so for the LCD-2.)
 
Both the HD800 and the LCD-2 rev.1 are too inefficient to use the 0 dB gain setting without compromising dynamics, as heard with really dynamic recordings like Beck's Sea Change or Michael Hedges' Aerial Boundaries. The OPPO PM-1 (PM-2), on the other hand, are efficient enough that I can only hear a slight difference in dynamics and no discernible difference in bass control or speed when toggling between 0 dB and 10 dB. This would be the same for the PM-3, also, since it's even more efficient than the PM-1.  The DAC alone might be able to provide enough power for the PM-3 (through the Aurix at 0 dB.)
 
Interestingly, I'm hearing a little more bass energy with the step-up transformer in the signal path than without. This again, is with the Aurix driven by the Octave MkII, where a synergy of some sort yields more bass in the high impedance HD800 than with the low impedance OPPO PM-1. So, although the bass energy is not boosted as much with the OPPO PM-1 as with the HD800, at the 10 dB gain setting, there's a detectable increase in bass energy in the PM-1 with the 10 dB gain setting vs. the 0 dB setting.
 
Still, there's something else happening when the step-up transformer is engaged (10 dB) - more of the euphonic tonal qualities that are so lacking in the HD800, but less needed by the PM-1, and even less so by the LCD-2 - for my tastes. Without the step-up transformer, the PM-1 is able to hear the DAC with little more than the attenuation provided by the volume control and some impedance matching, but if you want an even less "sterile" sound - of which the Octave MkII can hardly be accused, using the step-up transformer of the Aurix will deliver it - I am absolutely certain of this - tube-like goodness resides in the step-up transformer.  I couldn't determine this using my less efficient headphones because they "need" the extra power of the transformer, so 0 dB really isn't an option for them - if you want to maximize their performance overall.
 
In an attempt to quantify this "euphonic" contribution made by the Aurix transformer at 10 dB of gain, I'll say that I'm still convinced the Octave MkII makes a much greater contribution to euphonics, when used with other amps, than does the Aurix when used with other DACs, but the best increase in bass energy seems to come from pairing the Octave MkII with the Aurix while using the transformer, and they are more effective in this regard with high impedance loads than with low impedance.
 
I hope I'm right about all of this stuff.  When I start making really specific "observations" like this I get nervous, because I do feel a burden to be accurate for the sake of others who might act on what I write. Still, I'm saying it as I hear it, so hopefully my findings can be found reliable.
 

 
With that disclaimer, I'll stick my neck out a little farther by adding that the treble energy is rolled off a bit with the transformer in the signal path - great for HD800, OK with the PM-1, but not really desirable with the LCD-2 rev.1's already shelved highs.  It's very slight, however.
 
Mike

Mike, I'm not so sure that the "treble energy" is being rolled off a bit so much as the HD800 & PM-1 both have treble
peaks(I knew the HD800 did & didn't realize the PM-1 had 1 also) & the transformer appears to have a frequency "taper" so that it's not stepping up the entire FR equally .
 
I'm always talking about how headphones are "voiced" to accentuate different areas of the frequency spectrum, while all headphones are made to display the widest possible FR if they were "voiced" to not play "favorites" to various parts of the "entire spectrum" they would end up being "very"hard to sell.  Like everything else under the sun, if it doesn't grab your attention your first impression is "it's probably just not up to snuff !!! ". The HD800 errs on the side
having the ability to hear a "Gnat" flying from the extreme right side of an Orchestral sound stage to the extreme left side. To accomplish this technical fete of  brilliance, the ear has to be drawn away from other elements of aural dimensionality such as depth (& with that goes the sense of "scale") (I've never really thought about this,though...
just wanted to see if you were paying attention.. don't worry there's no test)
 
I think I started realizing the HD800 traits in comparison to my HE-6(which my respect for continually grows). I feel like I'm commiting sacrilege every time I don't come out & say the HD800 isn't the greatest thing since sliced bread. As much as we think of the HD800, we probably shouldn't use them a "Control Reference" if we plan on using other headphones
 
(Yes, I know I'm a "huge bag of wind"...but it keeps me occupied)
 
Steve

 

[beyerdude]

  I've been using the OPPO PM-1 with the Metrum stack - this morning - for the first time - for about 5 hours now.  It's efficient enough I've concluded I don't hear anywhere near as much loss of dynamics as I do with the LCD-2 (or even the HD800) when toggling between the Aurix 0 dB and 10 dB gain settings and adjusting the volume control to tape-marked positions established by volume matching with a white noise file and SPL meter.  I do hear better dynamics with the OPPO PM-1 at the 10 dB setting, but it's subtle, leading me to believe that the PM-1 is not quite efficient enough to deliver its best at the 0 dB setting - but nearly so.
 

 
10 dB Gain brings the step-up transformer into the signal path.
 
 

 
Marks on tape show the volume-matched positions for 10 dB (at left) and 0 dB (at right), for a measured 80 dB SPL inside the ear pads of the OPPO PM-1 playing a white noise WAV file. (Imagine those marks moved farther clockwise for the HD800 and more so for the LCD-2.)
 
Both the HD800 and the LCD-2 rev.1 are too inefficient to use the 0 dB gain setting without compromising dynamics, as heard with really dynamic recordings like Beck's Sea Change or Michael Hedges' Aerial Boundaries. The OPPO PM-1 (PM-2), on the other hand, are efficient enough that I can only hear a slight difference in dynamics and no discernible difference in bass control or speed when toggling between 0 dB and 10 dB. This would be the same for the PM-3, also, since it's even more efficient than the PM-1.  The DAC alone might be able to provide enough power for the PM-3 (through the Aurix at 0 dB.)
 
Interestingly, I'm hearing a little more bass energy with the step-up transformer in the signal path than without. This again, is with the Aurix driven by the Octave MkII, where a synergy of some sort yields more bass in the high impedance HD800 than with the low impedance OPPO PM-1. So, although the bass energy is not boosted as much with the OPPO PM-1 as with the HD800, at the 10 dB gain setting, there's a detectable increase in bass energy in the PM-1 with the 10 dB gain setting vs. the 0 dB setting.
 
Still, there's something else happening when the step-up transformer is engaged (10 dB) - more of the euphonic tonal qualities that are so lacking in the HD800, but less needed by the PM-1, and even less so by the LCD-2 - for my tastes. Without the step-up transformer, the PM-1 is able to hear the DAC with little more than the attenuation provided by the volume control and some impedance matching, but if you want an even less "sterile" sound - of which the Octave MkII can hardly be accused, using the step-up transformer of the Aurix will deliver it - I am absolutely certain of this - tube-like goodness resides in the step-up transformer.  I couldn't determine this using my less efficient headphones because they "need" the extra power of the transformer, so 0 dB really isn't an option for them - if you want to maximize their performance overall.
 
In an attempt to quantify this "euphonic" contribution made by the Aurix transformer at 10 dB of gain, I'll say that I'm still convinced the Octave MkII makes a much greater contribution to euphonics, when used with other amps, than does the Aurix when used with other DACs, but the best increase in bass energy seems to come from pairing the Octave MkII with the Aurix while using the transformer, and they are more effective in this regard with high impedance loads than with low impedance.
 
I hope I'm right about all of this stuff.  When I start making really specific "observations" like this I get nervous, because I do feel a burden to be accurate for the sake of others who might act on what I write. Still, I'm saying it as I hear it, so hopefully my findings can be found reliable.
 

 
With that disclaimer, I'll stick my neck out a little farther by adding that the treble energy is rolled off a bit with the transformer in the signal path - great for HD800, OK with the PM-1, but not really desirable with the LCD-2 rev.1's already shelved highs.  It's very slight, however.
 
Mike

The HD800 do sound more euphonic with the 10db gain switched on, I spent some time a-b ing between the two and there is a greater sense of dynamics in the music, more energy, more emotion/scale - the HD800 sound very similar through the Aurix at 10db to the WA6SE with a good set of tubes - so again I would absolutely agree it does to some degree achieve a tubelike sound (The WA6SE is one of the least tube like amps I have heard which for me is ideal for the HD800 but not for some other headphones like the DT880 600ohm) - The HD800 with a good OTL amp sounded syrupy and over euphonic - it was a solution too far to solve the shortcomings of the HD800 - initially very pleasing but the thicker meatier bass and less detailed/rolled off treble in the end destroyed all that I like about the HD800. 
 
I am not so sure about the treble roll off with the 10db gain enabled - it is not simply a matter of pure decibel gain - there is something else being added to the music (ahhhh so vague) - but maybe it  is simply a case of the additional voltage more suiting the HD800. I might revisit the gain switch and confirm this - as you said if there were any roll off then it would be very slight.

 

[zilch0md]

Hey Steve,
 
I always want to say, "I know what you mean," when I start my replies to your posts - it's subliminal!  

 
Quote:

  Mike, I'm not so sure that the "treble energy" is being rolled off a bit so much as the HD800 & PM-1 both have treble
peaks(I knew the HD800 did & didn't realize the PM-1 had 1 also) & the transformer appears to have a frequency "taper" so that it's not stepping up the entire FR equally .
 
I'm always talking about how headphones are "voiced" to accentuate different areas of the frequency spectrum, while all headphones are made to display the widest possible FR if they were "voiced" to not play "favorites" to various parts of the "entire spectrum" they would end up being "very"hard to sell.  Like everything else under the sun, if it doesn't grab your attention your first impression is "it's probably just not up to snuff !!! ". The HD800 errs on the side
having the ability to hear a "Gnat" flying from the extreme right side of an Orchestral sound stage to the extreme left side. To accomplish this technical fete of  brilliance, the ear has to be drawn away from other elements of aural dimensionality such as depth (& with that goes the sense of "scale") (I've never really thought about this,though...
just wanted to see if you were paying attention.. don't worry there's no test)
 
I think I started realizing the HD800 traits in comparison to my HE-6(which my respect for continually grows). I feel like I'm commiting sacrilege every time I don't come out & say the HD800 isn't the greatest thing since sliced bread. As much as we think of the HD800, we probably shouldn't use them a "Control Reference" if we plan on using other headphones
 
(Yes, I know I'm a "huge bag of wind"...but it keeps me occupied)
 
Steve

 
Going back and A/B-ing for treble differences again, using the PM-1, I have to repeat from my prior post:  "It's very slight, however."  
 
The OPPO PM-1 - which again is more efficient than the LCD-2 and HD800, with all three of them having, as you say, different "voicing," but due to its efficiency, is not suffering for lack of power at 0 dB as much as the other two headphones, thus making it a better candidate for comparing the two gain settings of the Aurix. 
 
Listening to cymbals, just now, in a 44/16 track of West Side Story, from the Buddy Rich/Maynard Fergusen album Two Big Bands Play Selections From West Side Story & Other Delights, and several 44/16 tracks from Diana Krall's The Very Best of..., toggling between 0 dB and 10 dB, I'm less convinced that I'm hearing an audible difference in the treble energy, but it's definitely not a difference in transparency - which amazes me.  I almost "want" to hear less transparency with the transformer in the signal path, just because it would make sense to have less transparency, but if I couldn't hear a difference with the HD800, I guess it's silly to think I could hear it with the PM-1.
 
Really, I'm splitting hairs to discuss the treble differences between 0 dB and 10 dB, compared to swapping in just about any other component - DAC, amp, or headphone can make a much more significant difference in treble response.  It's trivial.
 
And yes, I agree the HD800 is not the perfect headphone. Even on the Metrum stack, for my tastes, I'd still like a little more bass, but man, it's doing a lot of stuff just right - that my other headphones can't touch.  (I've yet to hear the HE-6 - and a whole lot of other headphones, of course.)
 
Mike

 

[zilch0md]

 
The HD800 do sound more euphonic with the 10db gain switched on, I spent some time a-b ing between the two and there is a greater sense of dynamics in the music, more energy, more emotion/scale - the HD800 sound very similar through the Aurix at 10db to the WA6SE with a good set of tubes - so again I would absolutely agree it does to some degree achieve a tubelike sound (The WA6SE is one of the least tube like amps I have heard which for me is ideal for the HD800 but not for some other headphones like the DT880 600ohm) - The HD800 with a good OTL amp sounded syrupy and over euphonic - it was a solution too far to solve the shortcomings of the HD800 - initially very pleasing but the thicker meatier bass and less detailed/rolled off treble in the end destroyed all that I like about the HD800. 
 
I am not so sure about the treble roll off with the 10db gain enabled - it is not simply a matter of pure decibel gain - there is something else being added to the music (ahhhh so vague) - but maybe it  is simply a case of the additional voltage more suiting the HD800. I might revisit the gain switch and confirm this - as you said if there were any roll off then it would be very slight.

 
Hey beyerdude,
 
Every time somebody mentions "something else [is] being added to the music" and that it's hard to describe, I'm reassured that we are all onto something that's really happening with the Aurix, despite being difficult to define, and it's very appealing, to be sure.  
 

 
 
I think it's the zero-feedback magic...

 

[knowhatimean]

Mike,
 
I know you're really not that interested in moving up to the Metrum Hex, but using just my Burson Soloist (which I've been describing as sounding "ever so slightly tipped to the cool side of neutral), I'm a little shocked at this moment. (While you like to speak of "tube goodness", i tend to speak about  "Hex goodness"
 
I'm listening to some large scale Choral pieces from one of my Anthology of the RCO live, Vol.5 discs ( on HDD) through the HD800 that is displaying "very" respectable "Hall ambiance without "shortchanging" the frequencies I normally expect it to. This is pretty unexpected to me for a few reasons..

The first being I really don't care for Choral that much, but this is pretty captivating (I think I may be listening for "Audiophile" purposes; the Hall sound is lush; I'm sure the Concertegebouw acoustic isn't famous for no reason.(I much
prefer the live Symphonic performances in these volumes (I may be up all night; I'll sleep tomorrow) Again, this was
the HD800 I'm talking about through the Soloist. (You had the Soloist correct ?)
 
For some reason I wasn't using the highest gain setting on the Burson. With the volume on the very first click of the attentuator the sound is just about ideal.with just a hint of the 800 resonance, but it's really not out of place on a live
concert recording with a full audience in front of 1 of best Orchestas playing in 1 of the best Halls in the World.
 
I may seriously have to curb my talk about the HD800s shortcomings (Even the applause sounds less like "crackling" with fuller dynamics). I really don't know what to make of this other than I think the Aurix may just push performance over the top for me. (If it were'nt for the fact that I don't live alone , I'd probably be standing & applauding myself; It's not cool to wake people up by applauding at 3 or 4 in the morning, I suppose)
 
Steve
 
(I might have to change my "username" to something subliminal that will mesmerize others to send me $$$$, as there's
little point to wasting opportunities that present themselves; now stare at those $$$$ signs "You're getting very sleepy)

 

[zilch0md]

Steve,
 
I found it at Amazon:  http://www.amazon.com/Anthology-Royal-Concertgebouw-Orchestra-Live/dp/B001JYDLMU/ 
 
Somehow, my tastes have not yet evolved sufficiently to actually enjoy classical music.  I tried getting into Wagner for awhile, because everyone says his compositions are more "accessible" to people like me, but even Wagner is just a chore. I cannot connect to it emotionally.  
 
That's quite the series of box sets - having been released every 10 years. Just from reading the reviews at Amazon, I'm envious of people, such as yourself, who have the capacity to enjoy classical music - I'm missing out on something epic with this 7-set RCO series.
 
The very low count of classical and country music in my CD collection leaves me feeling that I'm missing some genes in my DNA - that I'm somehow handicapped. The rest of my collection is thoroughly eclectic across many genres and yet I'm able to connect to all of it.  
 
But I'm really happy for you - genuinely - that you're so enjoying that music with your Hex > Soloist > HD800. I'm sure I would enjoy that chain as well, but I didn't have the HD800 when I owned the Soloist.  I only had the Audeze LCD-2 and Beyerdynamics T1 (among the flagships), using the DACmini CX as my DAC.  Looking back, I just didn't have the right DAC for the Soloist > T1.  The Soloist > LCD-2 was much more enjoyable, but even there, again using the DACmini CX as my DAC, I found the Soloist to be too laid back for my tastes - 10th row seating instead of front row - but its treble was really nice - smooth yet with great resolution.  Also - if ever there was a solids state amp that wants to be warmed up before use, its the Soloist. I wonder if that's related to its use of discrete components instead of ICs?
 
Mike 

 

[knowhatimean]

Yup, whenever I turn off the Soloist I'll set my Auraliti PK100 to "play complete library" upon turning the amp back on, & just let it play for 45min - 1hr before I even put my headphones on. Having everything connected to a Equitech 1.5Q Balanced Audio Transformer the only thing I  turn off is the Burson (if I'm going out for a while).
 
A few years ago I discovered that "Digital Components" sound much better if left on continuously ,rather than constantly turning them off & on (& its better for the components "health" in the long run). While it may take an hour for an ss amp to sound good , it may take much longer for a DAC to sound completely "Un - Digital" sounding (Although since I've had
the Equitech it is nowhere near as critical to wait the warm up time as it was when I was using a PSAudio PP; which I now use for my Video system)
 
My Hex only gets the best treatment & I'm rewarded with the treatment it affords me !

 

[zilch0md]

OK, revisiting the (trivial) topic of the Aurix' treble response at 0 dB vs. 10 dB gain, I've spent three hours this morning, beating this question to death.
 
Re-checking my volume-match marks, allowing the Aurix to play for an hour before I started, and using the HD800, not the OPPO PM-1, because it's the HD800 that doesn't play so well with my other amps and for which the Aurix was purchased as a challenger to the NuForce HA-200, I've concluded that for my Aurix, at least, with my HD800, and my ears, using my FiiO X5 Coaxial Out > Octave MkII as the source....
 
The 0 dB gain setting is slightly brighter than the 10 dB gain setting.  
 
The best track I've found for demonstrating this is Billie Jean, from Michael Jackson's album Thriller.  
 
I have to backpedal a little bit by reminding myself (and everyone else) that the HD800 is a high impedance load, for which Cees Ruijtenberg is quoted (in the 6moons review of the Aurix) as recommending users select the 10 dB gain setting, where low-impedance loads can get by with the 0 dB setting.
 
The Aurix has a constant 3-Ohm output impedance, whether you've selected 0 dB or 10 dB gain, so it's not about impedance matching as much as it is about sensitivity matching - in the sense that with 0 dB gain, you get 2V rms to the headphones (using the Aurix as a passive pre, but with 10 dB gain, you get 6V rms to the headphones. (Hint: 10 dB = a 3x gain and both the 2V and 6V figures assume the Aurix is getting 2V rms from the DAC).   
 
Thus, even though Cees Ruijtenberg has recommend using 10 dB gain for high impedance loads (an example of 600-Ohms is given in the specs), with the amp having a constant output impedance of 3-Ohms, he must not be concerned about maintaining the proverbial 8:1 ratio of load to output impedance - but rather, he's making the reasonable assumption that most high-impedance loads have less sensitivity and thus, need more power (specifically, more voltage from this amp).  And when he recommends 0 dB gain for low-impedance headphones (an example of 33-Ohms is given in the specs), it's again not about impedance matching, but rather a limitation on what his amp can deliver into a low-impedance load.  He's saying (my words): "Please don't make my Aurix run downhill (with a low-impedance load) on the 10 dB gain setting."
 
UPDATE:  As I mentioned below, I wrote Cees Tenenberg to ask whether it's "safe" to use low-impedance loads with the 10 dB gain setting he recommends for high impedance loads. Paraphrasing, his response indicates that either load can be used with either gain setting, without concern for hurting the amp.  He also confirmed that the output impedance is a constant 3-Ohms.  (It's not among the specs at the Aurix web page.  I had picked that up from the 6moons review.)
 
OPPO's engineers actually built power-limiting "intelligence" into the HA-1 such that the it's power curve is far from linear relative to load. If they didn't govern the amount of power it can deliver into low-impedance headphones, the HA-1 would overheat - like a car engine at nearly full throttle with the transmission in neutral. 
 
The HA-1 puts out 2000 mW into a 32-Ohm load (via its 4-Pin XLR jack), but only 800 mW into a 600-Ohm load.  Clearly, the HA-1 is in low-gear, so to speak, with its engine allowed to deliver full power under the greater load of a 600-Ohm headphone, but it's intentionally governed down to only 2000 mW into the lesser 32-Ohm load.  If those figures don't intuitively make sense at first consideration, have a look at the ratio of 600 / 32.  The resulting quotient is 18.75, meaning that a 600-Ohm headphone presents 18.75 times as great a load to the amp as a 32-ohm headphone.  If the HA-1 had a truly linear output relative to load, it would deliver 18.75 * 800 mW into the lesser 32-Ohm load = 15,000 mW rms per channel! That would require much larger heat sinks for Class A operation. Instead, the HA-1 is only allowed to deliver 2000 mW into the lesser 32-Ohm loads.  The HA-1 is allowed to run free into 600-Ohm loads.
 

 
I've sent an email to Cees asking him if low-impedance headphones can "hurt" the Aurix when set to the 10 dB gain setting and I will follow-up with his response, but in the end, assuming he says t's OK to use either setting with either load, I think the only "valid" way to compare the sonics of 0 dB vs.10 dB from the Aurix is to use a headphone that is efficient enough to be satisfied with the 0 dB setting's 2V rms - independent of the headphone's impedance - a headphone that doesn't actually "need" three times the power offered by the 10 dB setting - 6 V rms.  And I don't think the HD800 fits that requirement as well as the OPPO PM-1, despite the fact that it has a sensitivity spec of Sensitivity: 102 dB / 1V RMS, just like the PM-1.   (To my ears, the HD800 isn't nearly as content with less power.)
 
In the end, I'm hearing a greater difference in the treble energy between 0 dB (brighter) and 10 dB (less bright), using the HD800, than I've been hearing with the OPPO PM-1 when toggling the gain.
 
Mike

 

[knowhatimean]

The HD800 has always appeared pretty "Enigmatic" in terms of it Sensitivity Rating to me. The problem that I run into is they really don"t display the "less aggressive full tonality" until I've raised my volume level slightly higher than I prefer to listen at. This tonality seems to suddenly just "pop" into place. As great as they sound when I reach that very narrow window of volume, I can be certain I will be ear fatigued at some point when I'm done listening (As I am at this moment).
 
It seems to me they really respond much better to a higher gain , slightly lower volume setting. I make the mistake of finding the setting that sounds best & leaving it there, discounting that my hearing will "adjust / compensate" for a lower setting. You'd think I'd know better listening to extremely wide dynamic swings in the music I'm listening to.
 
I don't think using the 10db gain setting is really going to hurt the Aurix. I'm pretty sure that this gain setting is well within the transformers operating range. It would be poor engineering if this operational feature worked otherwise & I think Metrum Acoustics prides itself for their engineering as much as anything else.
 
(Almost forgot to ask, tonally how do the PM-1 compare to the HD800 in terms of the middle & lower registers)

 

[zilch0md]

  The HD800 has always appeared pretty "Enigmatic" in terms of it Sensitivity Rating to me. The problem that I run into is they really don"t display the "less aggressive full tonality" until I've raised my volume level slightly higher than I prefer to listen at. This tonality seems to suddenly just "pop" into place.  As great as they sound when I reach that very narrow window of volume, I can be certain I will be ear fatigued at some point when I'm done listening (As I am at this moment).
 
It seems to me they really respond much better to a higher gain , slightly lower volume setting. I make the mistake of finding the setting that sounds best & leaving it there, discounting that my hearing will "adjust / compensate" for a lower setting. You'd think I'd know better listening to extremely wide dynamic swings in the music I'm listening to.
 

 
This is perhaps the most insightful comment I've read on the HD800 - it makes so much sense!  I've never put this together on my own before, but seriously, this rings very true to me.
 

I don't think using the 10db gain setting is really going to hurt the Aurix. I'm pretty sure that this gain setting is well within the transformers operating range. It would be poor engineering if this operational feature worked otherwise & I think Metrum Acoustics prides itself for their engineering as much as anything else. 
 
(Almost forgot to ask, tonally how do the PM-1 compare to the HD800 in terms of the middle & lower registers)
 

 
More later, I have to run at the moment...  

 
 
Update:  I think you're right.  I'm still awaiting a reply from Cees regarding the use of low-impedance loads with the 10 dB gain he recommends for high-impedance loads.   I also asked him to confirm that the output impedance is a constant 3-Ohms, independent of gain or volume setting.
 
And... The PM-1 seems less affected by the Aurix relative to how it sounds on other amps, vs. the HD800's malleability.  The PM-1 does hear that hard-to-describe emotive force that the Aurix possesses, but its bass energy isn't lifted as much as with the HD800.
 
Mike

 

[zilch0md]

 
[snip]
 
I don't think using the 10db gain setting is really going to hurt the Aurix. I'm pretty sure that this gain setting is well within the transformers operating range. It would be poor engineering if this operational feature worked otherwise & I think Metrum Acoustics prides itself for their engineering as much as anything else.
 
[snip]
 

 
Quote:

  [snip]
 
I think you're right.  I'm still awaiting a reply from Cees regarding the use of low-impedance loads with the 10 dB gain he recommends for high-impedance loads.   I also asked him to confirm that the output impedance is a constant 3-Ohms, independent of gain or volume setting.
 
[snip]

 
See the update to my previous post.  
 
In other words, feel free to use any headphone with either gain setting.
 
Which brings me to mentioning my usual strategy - to use the lowest gain that provides sufficient power to maximize a given headphone's dynamics and bass control - to secure a lower noise floor.  
 
The Aurix is perhaps the first amp I've ever owned, to my awareness, where other traits get influenced by changing the gain while using a headphone that's efficient enough to not need the higher gain setting. I suppose it's because most amps with switchable gain aren't altering the signal path so dramatically. It's remarkable that the Aurix' step-up transformer sounds as "inert" as it does.  
 
Again, to put things in perspective for people who haven't heard the Aurix, switching to any other amp I own has more impact on the sonics than toggling the Aurix between 0 dB and 10 dB. 
 
Mike

 

[knowhatimean]

Mike, just a quick one (& that's tough for me as I can't seem to be economic w/ words)
 
I think that all the 10db switch may be doing is creating a better impedance matching "sweet spot" on the Aurix's transformer for what appears to be what the HD800 wants to see.
 
(Sounded like a well reasoned explanation when I thought it ; I'm not an engineer , so don't place to much stock in this,Cee's the man for this one)
 
Steve