[DaveNote]

I got my O2 headphone amp this week, and have been kicking the tires. It is just what I was looking for. An amp with absolutely no noise, which is a great change from the Schiit Lyr which had a pleasant sound. But I'm now happy to be rid of it because of a hum it had that plagued me from day one. I sent it back to the company and was told that they found no hum and that it might be a ground loop in my system. The O2 is noiseless played in the same room with the same equipment. No ground loop here.

The O2 also seems to be entirely transparent. Unlike the Lyr and several other headphone amps I've had, it has no coloration, but neither is it clinical or dull. The closest sound to it is, not surprisingly, the Grace Designs m902 I had, but which I, perhaps mistakenly, found unexciting. But I do recall, if you cranked up the volume on the m902, you could hear some noise. Not so with the O2. Dead silent all the way to the top.

Knowing how good the specs are, and how quiet this amp is, I'm confident that whatever differences in sound I hear from my headphones are in the headpones, not the amp.  I had a pretty good idea what the differences were in my headphones. But the O2 confirms and amplifies (no pun intended) those differences. I tried the ones I own, connecting the O2 to my Bryston DAC.

The LCD2 is a fairly dark headphone, with a wonderful full bass, but lacking in the high end. The O2 tells me all this, but emphasizes how non-linear the LCD2 is. It does not have an artificial or boomy bass, but the O2 tightens it. The midrange sounds good and rich, but is a little shaded or recessed. The high end, too, is recessed; not missing in action, but in retreat.

The Audio-Technica AH M50 is with the O2 what I took it to be. Bassy and boomy. The O2 brings this character out and to the disadvantage of this headphone. Not really so pleasant as I thought it was using it just with my iPad.

The O2 confirms my initial take on the AKG K550. This is a much more linear and balanced headphone than the other two. I have grown use to the very linear, highly balanced, sound of my Axiom M80 speakers, and the K550 emulates those qualities much more than the LCD2. Its sound does not have the weight and body of the LCD2, but no one frequency range predominates, a quality I crave. The bass does not reach as low as the LCD2, but is more controlled and, I believe, accurate. The high end is bright, but not harsh, and, again, accurate. To my ear, quite a bit better than the LCD2.

Since writing the paragraph above, I have changed my mind and assessment. I have written elsewhere that I use my main speaker-based system as the model against which I judge my other systems, including my headphone systems. That's why I mentioned my Axiom M80 speakers in the paragraph above. However, I based my initial assessment of the K550 and LCD2 on my memory of the M80 rather than side-by-side comparison, which, with apologies to the readers of this thread, was a mistake.

Having now done this side-by-side assessment, I can say that the LCD2 is a nearly dead-on match to the sound signature of my M80 speaker-based system. The LCD2 has a less distinct high end, and, therefore, is not as linear as the M80 system. Otherwise, it is remarkably close. The K550, by comparison is far more biased in the high end than the M80, with a comparatively rececessed bottom end.

I have made other changes in the OP based on this new comparison, as noted, below.

For fun I tried my old Grado SR80, which sounded much better than it ever did before. Much more controlled, with a lot more punch in the bottom end. I also pulled out my even older AKG K141, which AKG tells me is a 600 Ohm headphone. I needed to put the O2 volume nearly to the top. The K141 is better with the O2 than with other amps I've had, but not in the same league with my other cans. Still, no noise whatsoever from the O2 even at outrageous volume settings.

So, here I've found another surprise in terms of price/performance. The $250 K550 competes well with the $995 LCD2, and in some respects, to my ears it outperforms it in the high end. [phrase in italics added August 21]. The O2 confirms my initial take on the AKG K550. This is a much more linear and balanced headphone than the other two. I have grown use to the very linear, highly balanced, sound of my Axiom M80 speakers, the K550 emulates those qualities much more than the LCD2 Its sound does not have the weight and body of the LCD2, but no one frequency range predominates, a quality I crave. The bass does not reach as low as the LCD2, but is more controlled and, I believe, accurate. [phrase struck out August 21]. The high end is bright, but not harsh, and, again, accurate. To my ear, quite a bit better than the LCD2. The O2 at $150 does not have all the bells and whistles of the $1500 m902 I had, but purely as a headphone amp, I'd say it is better. And remarkably, the build quality is comparable to the m902. In fact, the volume control doesn't wiggle around as it did with the m902.

I ordinarily use the O2 in the mornings to listen to music through my iPad with my K550. With all connections in the front, it is not ideal for use with my main system, but has the merit of having a small footprint. I have thought hard about putting a large headphone amp with my main system, but have not found a way to place one conveniently in my system.

NwAvGuy is developing a desktop version of the O2 to be called the ODA, which will be just a little larger. With luck it will be out early next year. It will have rear connections, as well as a quarter inch headphone jack, likely some improvements in specs, and will operate with AC only. Because it probably will cost about $200 or less, and will be the right size, I am highly interested in it, especially given the performance of the O2. Indeed, it's so good, and inexpensive, I bought a second one to use with my main system pending the production of the ODA.

Dave

[JohnR]

Nice review

[eclein]

Excellent, I gotta try one....

[adydula]

Well I finished putting the ODAC in a case and added RCA outs as well as the mini jack in front...works well now I can insert into the 2 ch rig and see how it plays there!!




All the best
Alex

[DaveNote]

Excellent!  My O2 is in black, which matchs all my gear. But I think the silver has an advantage. It is easier to see the black buttons.

Alex, will you be getting an ODA? If so, will you buy or build?

Dave

[adydula]

Hi Dave!

I dont know yet....but I have the O2 amp I have it almost completed and buy another ODAC and will buy a case large enough to allow the batteries, the ODAC, RCA outs and larger headphone jack...all in one box.

I dont know how much longer it will be until the ODA will actually be out.

I might buy one later if it has any real or better performance stats than the existing O2 amp.

I dont think the ODA will be any better than the existing O2 amp....we will have to wait and see....

Alex

[DaveNote]

Hi Dave!

I dont know yet....but I have the O2 amp I have it almost completed and buy another ODAC and will buy a case large enough to allow the batteries, the ODAC, RCA outs and larger headphone jack...all in one box.

I dont know how much longer it will be until the ODA will actually be out.

I might buy one later if it has any real or better performance stats than the existing O2 amp.

I dont think the ODA will be any better than the existing O2 amp....we will have to wait and see....

Alex

NaWavGuy has written that the ODA should have some spec improvements. For a user like me, who wants to use it with a main system, its a 1/4 jack and rear connections would be preferable.

Dave

[fenderf4i]

I really love the O2 amp. I built myself a desktop version to hold me over until the ODA is released.

[DaveNote]

For those interested in this thread, please see the corrections I have made to the original post.

Dave

[JohnR]

Heh, I'm not sure that the cross-outs make anything clearer.. (they confuse me anyway)

But NM, I'm enjoying my O2 when I can. Remarkedly different to the Slee that I have on loan.

[DaveNote]

Heh, I'm not sure that the cross-outs make anything clearer.. (they confuse me anyway)

But NM, I'm enjoying my O2 when I can. Remarkedly different to the Slee that I have on loan.

I'm sorry John about the confusion. Bottom line, the O2 is great. The K550 is good, but not great: linear and accurate, but lacks body. Sounds very good on the iPad using the O2, but not nearly as good as my LCD2 on my main system using the O2. The LCD2 is great, but is somewhat lacking in the high end.

Hope that helps.

How would you assess the O2 against your Slee?

Dave

[eclein]

Can the DAC be bought built like the o2??

[DaveNote]

Can the DAC be bought built like the o2??

Yes. NwAvGuy has designed the ODAC and it has been released.

http://www.jdslabs.com/item.php?fetchitem=46

You can read all about the ODAC on the NwAvGuy blog.

http://nwavguy.blogspot.ca/2012/04/odac-released.html

Hope this helps.

It appears that the ODAC will be making the same kind of stir as the O2. But it is not on my shopping list since I don't need another DAC on my main system, I don't need a DAC using my iPad, and I don't listen to music coming out of a Mac or PC. But if I did need a DAC for my headphone use, the ODAC would be the first to consider.

Dave

[JohnR]

How would you assess the O2 against your Slee?

Hi Dave, at the moment I've set up a little "system" next to the sofa with a Pure i20 source into the O2 (or Slee) and then HD650s.

The biggest problem with the Slee was the noise - both electrical and acoustical - from its power supply. This is the "green" edition with a wallwart SMPS - it's basically junk. I solved (to my surprise) all of the noise problems by pinching the stock PSU from my Virtue ONE.2, with the aid of a DC plug adapter.

The Slee seems, in direct comparison to the O2, to be truncated in the treble. Bearing in mind that the HD650 tends that way anyway. At times, it sounds more natural, but before long I get to feeling that something is just not right. The O2 is more livable but a little less whole. So my conclusion at this point is that I prefer the O2 but need to work on the source in this "system" as I don't feel I'm getting the best of either of them at this point.

[adydula]

Hi Guys!

Well I was hoping to have my second o2 amp done, bu tunder inspection i found the gain switch had a metal support leg shorting to a via on the pc board and i had to destroy the switch to remove it and not damage the pc board. so now i have to wait until thursday for the new switch to arrive from mouser....lol

The LCD2's even thought are very flat in the Freq curve...sure does seem a little well flat on the high end...especially after listening with Grados....yeah I know the Grados are hot on the high end...

The ODAC can be bought from JDS for sure, that where I got mine for $99 assembled and put it in the neat little case and added the RCA inputs...you cant buy it in a kit form,, but can buy it in a case etc or in the O2 or have an existing O2 reworked to have one put inside.

Its a great dac, and have now used it in the main 2 ch system for a few days and its doing very well.

Alex

[DaveNote]

Hi Dave, at the moment I've set up a little "system" next to the sofa with a Pure i20 source into the O2 (or Slee) and then HD650s.

The biggest problem with the Slee was the noise - both electrical and acoustical - from its power supply. This is the "green" edition with a wallwart SMPS - it's basically junk. I solved (to my surprise) all of the noise problems by pinching the stock PSU from my Virtue ONE.2, with the aid of a DC plug adapter.

The Slee seems, in direct comparison to the O2, to be truncated in the treble. Bearing in mind that the HD650 tends that way anyway. At times, it sounds more natural, but before long I get to feeling that something is just not right. The O2 is more livable but a little less whole. So my conclusion at this point is that I prefer the O2 but need to work on the source in this "system" as I don't feel I'm getting the best of either of them at this point.

Two questions:

Can you explain what you mean when you say the O2 is a "little less whole" than the Slee?

I've never heard the HD650, but long ago I heard the HD600, which I passed on because it had a kind of veiled or muffled sound to me. Does the HD650, in your view, suffer from this?

Dave

[DaveNote]

The LCD2's even thought are very flat in the Freq curve...sure does seem a little well flat on the high end...especially after listening with Grados....yeah I know the Grados are hot on the high end...

Alex, as you know, I'm looking for a very linear and accurate headphone that does what rhe LCD2 does in the low end, but has a better high end. You've suggested the AKG 702 as a possibility, but I fear it, like the K550, might be light at the low end.

Do you have any other sugestions that might be even closer to the mark of what I'm looking for: high resolution, linear, accurate, with no one frequency range predominating over another?

Dave

[JohnR]

Can you explain what you mean when you say the O2 is a "little less whole" than the Slee?

No, I'm not really interested in defending what I thought was clear was a current impression. Go on with your absolutes.

[DaveNote]

No, I'm not really interested in defending what I thought was clear was a current impression. Go on with your absolutes.

I'm neither challenging you, nor do I engage in absolutes. Everything I've ever posted has been just my opinions, and I know that others might hold different opinons.

When I asked what you meant by a "little less whole" I did so because I've never read the term before and genuinely didn't understand your meaning. Whatever that meaning might be, I took it as a given that it would represent your impression and not an absolute. I wasn't asking you to defend your impressions - hell, I wouldn't try to defend mine - all I was asking for was an explanation of a term you used in giving readers your impression.  In short, while you thought what you wrote was clear, I was asking, respectfully, for a clarification of a term that was not clear to me.

Dave

[adydula]

Hi Again!

I could guess what a little less whole might mean but I might be incorrect...but would like to know as well.

The whole idea, the design, the specs, the freq plots, THD, IM etc, etc.....point to this little amp is basically about as perfect it can get at this price point....its "not in the picture" so to speak...thats what I like about it.

It allows you to hear your other stuff...from cans to source, both the music and how it was recorded and mastered. I find that lots of my music i really like is not that great in being  full range or has other nasty traits etc...poor mastering etc...this is why I look for the best recordings that I can find...

So if someone would tell me that this amp or the total setup, source, amp, cans then I would suspect anything but the amp in this situation that is contributing to the not as full" observation...

The source to me has been the biggest issue for me, followed by the cans....the amp is about as good as it gets for being neutral etc....

My switch is coming on thursday!! Yahoo!!

All the Best
Alex