Objective 2 Headphone Amplifier

Here's a photo of my O2/ODAC build in the wild. I purchased the kit from Audio Poutine here in Canada. It was my first build and what got me started on DIY audio.


(The eyeglasses are for scale only and sold separately. They're also good for reading fine print and soldering tiny components. Available at fine Costco stores everywhere.)

My appraisal of the O2 is pretty much in line with Solderdude's. The bass is tight and extended with plenty of impact. It definitely isn't thin, but, for folks with a preference for tubes, it will sound a tad dry at first. With the O2 set to no gain (i.e., no resistors in the low-gain socket), it easily drives my modded T50RP. And my K701 have never sounded better. It is dead quiet. I can't tell the difference when the amp is powered up or off (when music isn't playing, of course).

The build is straightforward and even confidence building for a neophyte like me. The documentation on NWAvGuy's blog is extensive and really walks the builder through the process, if he or she is willing to spend the time reading it.

One caveat: have a look at the photo and you can see how cluttered the front panel is. Cables everywhere, plus all the buttons and knobs. But you'll also notice that it sits unobtrusively on one corner of my very messy desk and even functions as an eyeglass stand.

Oh, two caveats. Audio Poutine pointed out that the two batteries rely on one charging circuit. Over time, this can lead to the two batteries not being symmetrically charged. After a year and a few months, the batteries in my amp no longer worked well (a loud buzzing when the amp was unplugged from the AC adapter and a right/left channel imbalance that even my ears could hear when plugged in). I just replaced them (the batteries. Not my ears.).

The batteries and the gain that must be set correctly are the biggest downsides of the design.

It appears as though Oliver has changed the charging circuit, at least that's what he claims.
It is something that is needed I reckon.

Indeed charging batteries in series could be a problem if discharging is asymmetrical OR too deep.
The protection circuit in the O2 should handle the deep discharge problem (like the Zigis has) by switching itself off.
Haven't looked at the circuit closely though.

Sorry for misidentifying Frans as the author, Ian. Nice writeup.

For the cost, the O2 is a darn nice amp. It is "neutral" to my ears, with all the good and bad that that implies. I find myself switching between the Project Sunrise II and the O2 regularly. And, if you don't mind my subjectivity and ambiguity, the PS II just sounds more intimate.

Because this is a DIY forum and there are probably other mid-fi enthusiasts like myself onboard, I'll say that if the O2 were the only amp I owned, I think I'd be perfectly happy.

It's not a problem, Mo!! I didn't put my name on it in any case and it's in Fran's amp section. That's what I meant by 'working closely together' to make the forum informative and friendly at the same time I guess.

Funnily enough, Frans looks at the way things are put together and analyses how it works in a similar way that I listen to music by pulling it apart to see how it's constructed!!

However, I have no option really but to review as me in a subjective kind of way, which I know some don't like. I try to be as honest as possible.

I have the Horizon amp which I also love a great deal. It's an amp with a musical 'character' which is very enjoyable. However, Frans may describe it as an amp with a tube, so it has a set of 'harmonics' imposed on top of the sound which creates what I'm describing - and also, the fact that some really don't like that effect!!!

Nevertheless, to my ears, it's the best open frame type amp around. I've tried the Bravo, Indeed, the whatever .......

They all fry themselves into an early grave. I cooked every one of them. The Horizon keeps going and sounds great.

For me, the 02 is an option to use with the T40 that Frans modded for me. It needs quite a kick to drive it properly on big peaks and the O2 does that particularly well for a portable.

So, for me, it means the T40 can be taken away from home and used nicely rather than compromise on the headphone because of the amp's lack of real driving power.

It is pretty neutral, I'd say. I can't really say it's fat in the bass or piercing in the treble. It seems very well balanced and as you say, not a bad price when you compare it with another one I have, the Neco.

Is low power on yours with the switch 'out'. It is better imo on low power and I have managed to find a pooint where the amp just begins to go into clipping on high power and switching to low resolves it. However, I'm doing a battery run at the moment, so it could be starting to lose it's 'edge'. Coming up to virtually 7 hours now.

OK. Thanks for that. I got the impression that it was a back end job!! That makes it easier then.

I have to admit, I'm tempted to get one of my own. It does work really quite well with the T40. I've done over 7 hours on battery now and it's still fine with it.

My O2 from JDS arrived today, and I had a chance to listen with three different headphones:

First, the bad news :

I started off with my modded Fostex T50 with Frans' active filter, and to my ears the O2 indeed, while quite clean and transparent, sounded dry, clinical, and lacking in mid-frequencies and presence. The bass, while there, I also found lacking. I couldn't help but miss my Project Sunrise with its full sound stage, realistic bass, and almost palpable three-dimensionality!

Next was my HE-500 with Frans' active filter. Pretty similar results as above: to my ears too thin, lacking in musicality, smaller sound stage, and reduced bass presence.

I then hooked up my heavily modded and damped Denon 2000 with 5000 mahogany cups, and the O2 truly brought them to life! . A perfect match! I never before heard my Denon 2000 sound that good. It was all there! Lows, mids, well balanced highs, and a wonderfully wide sound stage. I am truly amazed at the synergy! While initially being disappointed with the O2's performance with the first two excellent HPs, I now believe that it was worth buying it for that reason alone!

So, the good news is that the O2 does have a place in my arsenal. While it does have more power and headroom than my portable Neco, and as a portable (transportable) it will make a better choice for me, and it sounds fantastic wirh my modded Denon HPs, it does not have anywhere near the power and headroom or the sonority of my Project Sunrise! The latter, equipped with my favorite ECC88 Telefunken tube, to my ears, remains unchallenged.

Of course, the above are initial SUBJECTIVE impressions of the OBJECTIVE2, and after some burning in, the latter may change, or my ears may become more accepting and forgiving (although, I don't expect by much), this may be subject to change (with notice).

Cheers!
Israel

The Sunrise IS configurable with jumpers. There are 2 settings: 10 Ohm and 68 Ohm. On the very rare occassiion that I would use my K701s, which was a year ago, I would change the output resistance setting to 68 Ohm plus adding an inline output resistor of 52 Ohm for a total of 120 Ohms.



I am, however, amazed at how great it sounds with my modded Denons with mahogany cups, which I take along when I have a long session at the cancer center. With the O2, they sound incredible! No thinness, a nice musical sound, lows, mids, highs, and presence with a full expanded sound stage - almost as good as my HE-500 with Frans' filter!



IMHO, it is more a matter of synergy, or to put it a little more crudely and cynically, a matching or a ying/yang of compensations - a kind of give and take of deficiencies - one makes up for what the other lacks, and vice versa! A marriage of a sort, not necessarily based on love, but perhaps a symbiosis! ;D. But it works!

Cheers!
Israel