Yes, this counts as mini for me. I’m prone to rambling...
Since Lord Voldemort was kind enough to send me one of his Objective2 prototypes in return for being one of his loyal minions (or maybe just giving him some useful advice from a different perspective) I figured I should write up some impressions since there are only a few “in the wild” so far.
I received a fully assembled unit complete with enclosure, batteries, AC adapter, and even some nice graphs verifying its performance. The gains are set to 2.5x and 6.5x. I’ve done most of my listening so far with my modded Fostex T50RPs and my Shure SE530s from either my Cowon D2+ or Maverick D1 as my source. Music is all over the place and includes metal, electronica, Jpop, and classical plus the anime and movies that I watch with my T50RPs as primary transducers. Other headphone I own and used with the O2 are the Sony XB700, Yamaha YH-3, Beyer DT1350, and Koss KSC-75.
I’ve had the O2 a several days now and I’ve been listening to it a lot so I thought I should write something about it.
I’ll start with the pros. First is the super low noise. It might not be a big deal if you only use fairly inefficient headphones but if you mix and match them with sensitive BA IEMs it’s a pretty useful trait. The O2 has no background hiss with my SE530s. Even after putting on my -30dB (allegedly) hearing protectors over my Shures and going to a quiet room I still didn’t hear any hiss. I still didn’t hear any hiss after connecting my D2+ which normally makes the SE530s hiss quite audibly when directly connected. The much criticized gain structure turns out to be good for something after all, at least if you like to use IEMs while stationary like I do.
If you plan to use the O2 with sensitive BA IEMs often and don’t want to use a digital volume control I’d suggest going with 1X gain for your low setting. I knew 2.5x would be too high to avoid using a digital volume control in some cases but I have this perverse desire to use all my headphones with the O2 from both my home and portable sources so I had to make a sacrifice somewhere.
I’ve read a few people who were concerned about interference from cell phones but even GSM phones won’t cause enough interference to blow your ears out with IEMs. Even with my GSM phone sitting directly on top of the O2 the interference isn’t any louder than the music when listening through my SE530s.
Other people have expressed concerns about transients during powering on and off. The do exist but they aren’t objectionable, even with my SE530s. There’s a small click when powered on and a brief thump when powered off.
Another small favor is the non night-vision destroying red power LED. I fondly remember the days when the color temperature of my room at night wasn’t bluer than during the day and can only hope that the O2 will usher in a new era of sanity...
By now everyone’s probably wants me to cut to the chase and start talking about how it sounds. This might be the most important part, but its also pretty anti-climactic. As far as I can tell it doesn’t sound like much of anything. Its not harsh or clinical or sterile and its not warm or lush either. Its clean and clear. To me it sounds like music, or at least the combination of my source and headphones.
I could wax poetic or philosophical but it wouldn’t really change anyone’s mind on the philosophy of sound reproduction. The short answer is that if you’re looking for transparency on a budget the O2 seems to fit the bill for the majority of combinations of users and headphones.
The O2 powers all my headphones quite well. I don’t have any super-inefficient ‘phones like the HiFiMan planars but my Yamaha YH-3 and Fostex T50RPs aren’t exactly paragons of efficiency either. My T50RPs still get plenty loud (and stay clean while doing it) even after eating up more than 12dB of headroom between EQing the up the sub bass and other DSPs for watching movies from the ~2.2V line out from my D1 with a gain of 2.5x. It doesn’t have tons of headroom after that so if you’re also fond of such things you may want to rule out the O2 for use with the less efficient models like HiFiMan planars. Applying the same sort of aggressive EQ to high dynamic range music could also eat up the O2’s headroom pretty fast too. If I wasn’t trying to use my O2 with such a large variety of stuff (inneficient headphones with portable sources as well as super efficient headphones with normal sources) I could have had the gain matched better and got another 1.5V out of it so matching it to your source is something to keep in mind if you have particularly inefficient ‘phones.
Besides that its only major weakness is that some people might think that its too large to be considered “portable”. It probably won’t fit in your pocket, but there are lots of people who carry larger volumes of “portable” gear so its really an individual choice. Given its quality and size I think it falls into a category similar to 17+ inch “desktop replacement” laptops. It can be either or both depending on your needs and what you're comfortable carrying everywhere. In a lot of situations it could be the only headamp you’ll need.
In the end, I’m going to keep my Practical Devices XM6 as my portable amp due to its profusion of extra features (I can’t live without crossfeed) even though I prefer the O2 as a straight amp. At home I can do the crossfeed in software and in that situation the O2 has replaced my Maverick D1’s built in amp.
Overall, I can recommend the O2 to people who are looking for transparency and don’t need any extra features like crossfeed or tone controls.
Edited by maverickronin - 4/4/12 at 8:28pm