So is this the ultimate small sized amplifier then, I hear you ask? No, not to me I’m afraid. For my personal liking the bass part, even though its quality and depth is very good, is missing some punch and impact. But the bass isn’t the only thing bothering me actually, there also is something bothering me with the mids . They sound a bit thin to me to be honest, I just feel like I am missing out on something using the O2. It isn’t bad sounding, and I’m sure lot’s of people love it, but I’m not one of them, I’m missing something to enjoy what I’m hearing. Now the level in which this bothers me depends alot on the headphone used. With the Sennheiser HD650, I even experimented with EQ’ing to get to make it to sound as it usually does with a whole bunch of other amps, but I quickly abandoned that attempt. I really don’t find the Senns to pair well with the O2. The Hifiman HE-400 with its thicker mids and powerful bass, does very well with the O2. The O2 softens the parts I find the HE-400 to focus too much on and as a result you get a nice match. Good detail, soundstage and clarity, as good as it gets on the HE-400.
Its bigger brother, the HE-500 I also appreciated with the O2, but not on the same level as the HE-400. In the beginning my ears had to adjust a little to the O2 mids and bass, as explained before, but once I got used to it I quite enjoyed the HE-500 with the O2. I won’t call it my favorite amp with these headphones, but the O2 made it sound pretty good. The volume dial has to be turned quite a bit more to get the same volume levels as with the HE-400 but you won’t need the high gain position at all. Bass detail and depth is great but I do prefer the HE-500 with a tube amp which makes the mids on the HE-500 so much smooter and enjoyable. That’s basically my biggest shortcoming of this combo, the mid section.
The Beyerdynamic T70 was the worst one combined with the Objective 2. Thin, no bass, no mids and way too bright. Absolutely not recommended. A lot of people on the web swear with the O2 and Audez’e LCD-2 combination (I never heard NwAvGuy to make such claims) but I can’t find myself in that. The O2, who supposedly can take on amps 3 to 4 times its price, can hardly get out of the LCD-2 what I can with my other amps like the Violectric. Bass depth and rumble is mediocre and where did those gorgeous mids of the LCD-2 go to? In my opinion it would be a shame to use the O2 with such an excellent headphone. Probably a lot of others will enjoy this combination as it is very neutral and detailed but that’s not enough to make me enjoy the LCD-2.
It’s a good amp but it has its own character, neutrality being its absolute focus and compared to other amps the before mentioned bass and mids just aren’t as nice. In its defense, a DIY’er should be able to build the O2 for around $50, and for that money it is impressive. My personal preference would be a mix of the O2 and he C421. The O2′s clarity, soundstage and details with the C421′s bass, mids and “fun feeling”. That would be great! So overal I am a bit disappointed with the O2, it certainly isn’t bad and it is neutral as it’s supposed to be but I expected a more enjoyable sound. If I had to choose between the C421 and the O2, the JDSLabs’s creation would win, even while the O2 is definately the better technical amp but with every single headphone I tried, the C421 sounded much more enjoyable to my ears and that’s what I care about most.
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