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86% would recommend to a friend 
Drop O2 Headphone Amplifier
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Drop O2 Headphone Amplifier
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Product Description
In 2011, audio engineer NwAvGuy published a blog post titled “O2 Headphone Amp,” in which he outlined his philosophy on defining sound quality and detailed his ideal audiophile circuit design. Our version of NwAvGuy's famous O2 amplifier, the Objective 2 Desktop Edition features updates based on feedback from the community Read More
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(335 reviews)
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keyboard_arrow_downTreyApples
0
Jan 11, 2022
TiffanyPoodleslideHello, I really appreciate your review and decided to get this amp specifically for a pair of 600omh 880's I was gifted, but I don't feel like I'm getting the performance that you alluded to in your review. Can I ask what your setup was? I wrote a review after trying it out for a little bit and I noted how I feel as though only at max volume settings do the 880's become just enjoyable enough but was sort of let down. Sorry to use you ask tech support but I figured you had a particularly specific insight that would be useful to me.
TiffanyPoodleslide
1402
Jan 18, 2022
TreyApplesThe OLD click-wheel iPod Classic 5.5 with a massive,(2gauge), gold wire handbuilt interconnect using Mogami Pure parts. This is the size of many speaker cables lol. I use the biggest cable I possibly can in an effort to reduce impedance. The iPod has the
best audio engine they ever used in an ipod.
One of the first places I go to troubleshoot amplitude/output power is sorting my transfer train, i. e. any cables and jacks that can act to throttle electron flow. Like, no point in having a lovely set of british speakers with high impedance drivers,(think Celestion SL6’s with copper dome tweeters), if you don’t serve them with low impedance cables and a higher output amplifier.
Headphones are just little speakers that you strap to your head, after all.
Start by troubleshooting that, and having the patience to allow for adequate run-in of your system, cables and all.
Also; you won’t see me hooking up my mini-pin iem jack from my iMac with a tiny little earphone cable to the input on a dac/amp.
Big-azz cable all the way,baby!
:-)
(Edited)
TM80
58
Apr 6, 2018
checkVerified Buyer
Didn't have that high expectations on this amp but it surely surprised me with the open and accurate sound it produced. I use an Audioquest Dragonfly v1.2 DAC with this and they sound really good together.
My main headphone amp is the Little Dot mk II tube amp which has a lovely warm sound that just flows through the songs. The O2 is a strong rival to the LD though with it's accurate but easy sound. A lovely pair specially to the Sennheiser HD6XX headphones.
Definitely recommend getting it! But please fix the damn plug to an EU version (or atleast provide the possibility to get one).
EDIT (03/2019):
The more I've used this amp the more I love it. This has almost completely replaced the LDmkII as my daily driver. And now I actually prefer it paired with the HifiMAN HE-400 so I can also highly recommend the Massdrop x HIFIMAN HE4XX + O2 amp combo.
(Edited)
phoenixsong
1055
Aug 20, 2018
checkVerified Buyer
The JDS version is better with low volume level matching. I ended up getting one from them and never looked back. Sold off this one. Still, it's a nice product :)
FrankN
13
Mar 14, 2018
checkVerified Buyer
The Objective 2 headphone amp which was designed to rival or beat headphone amps costing $1000 plus accomplishes that in spades. The sound is big, clear and accurate. The dynamic impact throughout the frequency spectrum needs no improvement. It drives my AKG 812s with ease.
The O2’s no-nonsense metal enclosure is not flashy, but well-built, solid and more than adequate. I bought the original when it was first introduced and I just purchased this Massdrop model. I also recently purchased the model that has the on-board DAC called the ODAC. Again, stunning value and performance. Either would be the perfect gift for any audiophile.
ILikeAcid
285
Feb 13, 2019
Yes! It ABSOLUTELY works without a DAC!
(Edited)
RaspberryAntelope
11
Jul 5, 2019
checkVerified Buyer
I've been using this amp for the last few months to power multiple pairs of headphones that I own. The three main pairs that I use are the Sennheiser HD598, the HD6XX and the Hifiman HE-560. The amp itself seems to have a pretty low noise floor, as even plugging in pretty sensitive IEMs doesn't transmit anymore than a tiny amount of noise, if any.
The 598's do sound a bit more open, and although this isn't a huge difference, it is pretty nice since these are my headphones of choice for playing games, especially positional audio games like CSGO. The bass response of the 598's, which isn't necessarily lacking, definitely sounds stronger when hooked up to the O2.
The 6XX sounds pretty amazing with this amp. Obviously this isn't a headphone you'd typically want to run without an amp anyway, but it pairs very well with the O2. Compared to listening to them through a non-amplified source like a phone, the only real way I could describe it accurately would be to say it feels like the 6XXs almost "open up" as if they were removing a shroud that was covering them previously. Everything sounds more clear, more powerful, and the channel separation seems much better too, although that could be placebo or simply the combination of being able to hear more detail.
The HE-560s are probably the most power hungry headphones I own at the moment, and despite the O2 amp only putting out somewhere between 300 and 600mW at the 45Ω impedance and 90dB efficiency, it sounds amazing. Bass hits hard (as planars should), the treble is clear and sparkly, and mids are warm and enveloping. As much as I'm sure the 560 could take more power from a bigger amp, I have trouble parting with the money to buy one since it already sounds so good off the O2.
Bottom line, this is a phenomenal purchase, especially at <100$, and I'd highly recommend this amp to anyone. I'm actually thinking of getting one to put on my nightstand for use when I don't want to have to sit in my computer chair to enjoy my music!
(Edited)
Evshrug
3772
Community
Nov 3, 2020
Have you tried with the 50 Ω Fostex T50RP yet? They may be low impedance, but they’re actually “quieter” at the same volume setting as a 600 Ω Beyer DT880 I had, and that’s because the T50 lRP’s sensitivity is low.
For most headphones, medium gain should suffice 👍🏻
phoenixsong
1055
Nov 3, 2020
EvshrugOh yeah, insensitive planars are the worst. Good thing nortelc's asking about the HD6XX
(Edited)
Typhoon859
141
Mar 29, 2018
checkVerified Buyer
By far the worst sounding amp *I own. If you can afford this, you can afford the FiiO amps, starting with the E10K and above.
At first I couldn't figure out how this could be (what I will describe later), but it's as if (possibly actually the case that) nwavguy cheated in how he designed the circuit to result in such low output distortion and generally such high specs/benchmarks. What I mean is, to achieve such low distortion (on paper), it's not just the integrity of the circuit which was maintained through careful design and component selection, but the actual source coming in is also directly tampered with where whatever effects of the circuit are attempted to be negated/reversed. (Having not analyzed the circuit myself however, I couldn't exactly tell you whether it's messing with phase/polarity or what it could actually be).
I get this idea from the fact that the sound is like that of no other low, mid, or high-end amp I've ever experienced. In a phrase, it literally sucks the life out of the music coming through it. As an audio engineer, I can tell you that when sound is being tracked and recorded (by whatever methodology), at no stage does it EVER sound like it does on the output of this thing. This is particularly more evident/noticeable is using transparent, neutral, and otherwise sensitive headphones (like the Brainwavz HM5's for instance) and with full-range frequency content like Metal music.
In nwavguy's fight against tube amps, against "audiophile" perspectives on all types of audio gear/technologies, and perhaps against whatever other forms of overpriced snakeoil (which I side with him on, even if not entirely what he actually builds upon in his conclusions), he unfortunately actually managed to prove those people right. I have heard plenty of horrible sounding solid state amps which create this unpleasant kind of odd-ordered harmonic distortion, particularly in the higher frequencies, forcing you to keep the music at clinically low levels, as instead of getting fuller, it gets more unpleasant as it gets louder, but this isn't exactly what people would typically comment on this point. People would often say that solid state amps have a "cold" or "digital" sound to them - no liveliness to them. Well, whatever that means, the O2 amp would actually be what would fit such a description. I am quite honestly embarrassed for having fallen into the hype myself and used this amp as an example of greatness in debates in the past, prior to even having heard it myself.
While I am highly analytical and into objective measurements of things (not just in audio), I don't think we're there yet in our tools to accurately reflect the psychoacoustic phenomena and other aspects of human hearing which interpret an array of sonic qualities which simply aren't represented in any chart - that is to understand how a piece of equipment functions relative to our real-world perception. I can definitely say that this amp is not neutral and imprints a definite signature on most any song, adding almost like an inverse distortion - removing certain harmonics and other characteristics which is largely what places you within the context of what you're listening to. Nothing in nature or in the recording process I've ever heard has otherwise ever had this sort of characteristic or left this kind of sonic imprint. I was able to AB test the O2 against any other amp and easily identify it - unfortunately, the heuristic being used to do so not exactly being one which positively reflected on the amp.
Whether or not the formalization of what exactly is wrong with this amp is correct doesn't really matter when the general unpleasantness can be identified using a blind test and experience is further able to isolate the difference in characteristically negative ways. I hope this fact can be appreciated and this review is otherwise helpful for those making their consideration for buying on whatever basis.
(Edited)
Recommends this product? No
Caiz
23
Oct 23, 2018
"There's no point in me trying to change it as you're certainly not here to learn anything from me. With respect to my previous comment, it was intended to reference points I've already made in my initial review, as your perspective was literally the one it was meant to challenge as I find IT to be the one that's misleading - misleading even me, even though I already knew better. My review is intended for people still trying to make up their minds."
firstly,, im here to elarn, and your slandering my character with this besmeachness, and thats totoally out of bounds.,, i've asked you to explain what exactly you mean, for the very fariness that you might teach me something, yet you now dodge anwering my questions and challenges directly and serve an excuse, lambasting me as a person unwilling to learn, which is obviously false. Secondly a perspective cant inherently be misleading, your argument that "my perspective" is misleading for you makes no sense to me..
You make your post, not as a review of the product, but to challenge the perspective the all items representing sound reproduction are measured, especially regarding the role of an amplifier? That is, you feel there are unmeasured figures in the reproduction of the sound samples and that my perspective the the reproduction is measurable is misleading to you?
" measure of THD (total harmonic distortion) doesn't tell you WHICH harmonics or where (though obviously you can find graphs which do highlight how much in what specific frequencies)." yes and while the graphs are viewable, this is just in terms of distortions, which is measureable against that characteristic of other amps, like one persons purse might have 1 loonie and 3 quarters, and represent a total value of one dollar and seventy five cents, someone might elsewise have three dollars, these are real values, just like thd, it's pretty easy to see the graph and pic a proffered plot..,
"This is because sounds in nature very uncommonly have this kind of harmonic balance, and we are very keen to sense this. In other words, you can have TWICE as much distortion, but if it's even-ordered, we are likely to perceive it as CLOSER to the original sound (as originally captured) than we would with half as much if it's odd-ordered."
lol okay, but what d you mean to say this has to do with this particular amp then?! in so much as any other amp?
"As I otherwise mentioned, I don't know what exactly the O2 amp is doing to result in the kind of sound I was describing, for reasons you agreed with me on which we don't have the tools for, but I picked it out every time in the conducted AB test (with help from a friend who ensured there was no possible association I can have for where the sound is being sourced from). Take from this what you will.
" well then i simply chalk your experience up to an improperly setup implementation, something you have setup there, i say, is obviously broken. Measure your output impedance of your reference condition is too high for your phones, or maybe your going out of bounds with this amp and your power draw,. not sure, maybe your test setup for your ab comparison is not well done, or your other amp is broken, but the amps jobs is to accurately reproduce the samples, and shouldn't sound noticeably then any other quality amp., besides a bit of distortion, especially when your testing mono, 1 channel at a time., so if something is coloring the music, so things sound different to you, your equipment i must contest is; improperly setup. One amp shouldn't have anymore bass, or any more trebel, then the other quality amp. right? So long as the power demand is there, the 02's been shown to reproduce the frequencies evenly well, at various loads eh., unless your convincing yourself of things, and then thats hardly fair on the amp. Do you agree that any given test tone should be reproduce the same between the 02 and any other quality(accurate in reproducing source material) "amplifier"? Like, if you need to you can ytest reproducing a 60hz sound at reference condition, and see if your system pics up that 60hz sound at the correct volume, once you've calibrated your setup. even throw some loads in there
You make your post, not as a review of the product, but to challenge the perspective the all items representing sound reproduction are measured, especially regarding the role of an amplifier? That is, you feel there are unmeasured figures in the reproduction of the sound samples and that my perspective the the reproduction is measurable is misleading to you?
" measure of THD (total harmonic distortion) doesn't tell you WHICH harmonics or where (though obviously you can find graphs which do highlight how much in what specific frequencies)." yes and while the graphs are viewable, this is just in terms of distortions, which is measureable against that characteristic of other amps, like one persons purse might have 1 loonie and 3 quarters, and represent a total value of one dollar and seventy five cents, someone might elsewise have three dollars, these are real values, just like thd, it's pretty easy to see the graph and pic a proffered plot..,
"This is because sounds in nature very uncommonly have this kind of harmonic balance, and we are very keen to sense this. In other words, you can have TWICE as much distortion, but if it's even-ordered, we are likely to perceive it as CLOSER to the original sound (as originally captured) than we would with half as much if it's odd-ordered."
lol okay, but what d you mean to say this has to do with this particular amp then?! in so much as any other amp?
"As I otherwise mentioned, I don't know what exactly the O2 amp is doing to result in the kind of sound I was describing, for reasons you agreed with me on which we don't have the tools for, but I picked it out every time in the conducted AB test (with help from a friend who ensured there was no possible association I can have for where the sound is being sourced from). Take from this what you will.
" well then i simply chalk your experience up to an improperly setup implementation, something you have setup there, i say, is obviously broken. Measure your output impedance of your reference condition is too high for your phones, or maybe your going out of bounds with this amp and your power draw,. not sure, maybe your test setup for your ab comparison is not well done, or your other amp is broken, but the amps jobs is to accurately reproduce the samples, and shouldn't sound noticeably then any other quality amp., besides a bit of distortion, especially when your testing mono, 1 channel at a time., so if something is coloring the music, so things sound different to you, your equipment i must contest is; improperly setup. One amp shouldn't have anymore bass, or any more trebel, then the other quality amp. right? So long as the power demand is there, the 02's been shown to reproduce the frequencies evenly well, at various loads eh., unless your convincing yourself of things, and then thats hardly fair on the amp. Do you agree that any given test tone should be reproduce the same between the 02 and any other quality(accurate in reproducing source material) "amplifier"? Like, if you need to you can ytest reproducing a 60hz sound at reference condition, and see if your system pics up that 60hz sound at the correct volume, once you've calibrated your setup. even throw some loads in there
Typhoon859
141
Oct 23, 2018
CaizMaybe you are here to learn, but not from me. You couldn't have rode in on a higher horse and couldn't have been more smug, demeaning, and belittling - further being needlessly selective in what you were singling out, strawmanning the whole of anything I said (in a derogatory and slanderous fashion) and furthermore presumptuous. No reason I shouldn't minimally call you out on that or otherwise legitimized it by simply going with it. I waited till your next comment to see if you would tone it down but instead you actually did the opposite and double-downed. If you bothered to check yourself first, I wouldn't have had to say anything. The internet creates the illusion that anyone can be talked to by anyone else as if to a clueless child.
You're continuing to do the same thing. Yes, a perspective that's offered as the truth can be misleading to somebody else. No, there's no reason to assume an improper setup which at this this point I have to submit is a rationalization, precisely in order to dismiss anything being said - again having used reductionism and strawman tactics. And no, I'm not dodging, as I actually engaged this your nonsense and explained myself further, so if anyone with sense were to come across this, they might possibly retain some further value. Any further reason I'm not responding to anything else is because your questions aren't questions; they're underhanded insinuations.
You made this personal from the very first post, so now you get in return a response to the undertone your commentary has had throughout, which was way more substantial than anything you actually said, unfortunately...
Feel free to further vent your poorly constructed babble with this uncooperative mindset you've developed in your social approach/interactions. Hope one day you're surrounded by better people with whom this isn't the established norm, as is all it could possibly be with you quite literally open the conversation in this way (doesn't matter how good YOU think the people are). A mentality like this is completely a product of the environment, so I don't blame you, but I don't care to further engage. Nothing productive about it and whether consciously or not, you're forcing it to be even less so - again, the furthest thing from wanting to learn anything from me, regardless of your purported intentions.
You're continuing to do the same thing. Yes, a perspective that's offered as the truth can be misleading to somebody else. No, there's no reason to assume an improper setup which at this this point I have to submit is a rationalization, precisely in order to dismiss anything being said - again having used reductionism and strawman tactics. And no, I'm not dodging, as I actually engaged this your nonsense and explained myself further, so if anyone with sense were to come across this, they might possibly retain some further value. Any further reason I'm not responding to anything else is because your questions aren't questions; they're underhanded insinuations.
You made this personal from the very first post, so now you get in return a response to the undertone your commentary has had throughout, which was way more substantial than anything you actually said, unfortunately...
Feel free to further vent your poorly constructed babble with this uncooperative mindset you've developed in your social approach/interactions. Hope one day you're surrounded by better people with whom this isn't the established norm, as is all it could possibly be with you quite literally open the conversation in this way (doesn't matter how good YOU think the people are). A mentality like this is completely a product of the environment, so I don't blame you, but I don't care to further engage. Nothing productive about it and whether consciously or not, you're forcing it to be even less so - again, the furthest thing from wanting to learn anything from me, regardless of your purported intentions.
JoeW901
8
Apr 1, 2019
checkVerified Buyer
Not sure why the love for this amp. Every source I run through it sounds muddier with a reduced soundstage. Pretty disappointing. Much better quality just plugging straight into the Grace Design SDAC or any other original source. I don't have any high-impedance headphones, my HD 598's at 50 Ohms are the "most" demanding, but all I hear on them is more volume and less quality. Perhaps if I get higher-impedence someday this will have more value? Throwing in the closet of misfit toys for now.
Highdrone
31
Mar 9, 2019
checkVerified Buyer
The only thing that I have to add to all these positive reviews is that if you open it up from the back (5 screws), there's a spot for two 9v batteries. This makes it kind of portable. I'm sure it's common knowledge to all you audiophiles, but I have a feeling that there are plenty of ear virgins such as myself purchasing this amp.
(Edited)
Artismo
461
Oct 3, 2018
checkVerified Buyer
Clinical, accurate, detailed, and clean with a low noise floor. It brought back the missing bass impact to the HE4xx, but kept it’s intimate sound. The HD58x also has more bass impact, but not as apparent as the HE4xx, and the sound stage opened up more.
DAC: Topping D30 Cans: HD58x, HE4xx Cables: Mogami RCA, Neutrik soldered connectors, standard PS, standard USB Songs: Klingande, Jubel; Robin Schulz, As the Sun Goes Down - 24bit 192Khz FLAC
DAC: Topping D30 Cans: HD58x, HE4xx Cables: Mogami RCA, Neutrik soldered connectors, standard PS, standard USB Songs: Klingande, Jubel; Robin Schulz, As the Sun Goes Down - 24bit 192Khz FLAC
Josepfe
49
Apr 23, 2020
Hi :-) here I am back more than one year later. To let you know that I more or less followed the path that you marked with your comments.
I currently own the 6xxs since March 2019 and I am very happy with them. I also purchased and kept the AKG 702, the Beyerdynamic DT 990 pro, the Audio Technica MSR7 NC, the Grado SR2i and from today the Hifiman Sundara.
I have two weeks to test the Sundaras, but I think that I will keep them. It is nice to have headphones of different sound profiles and I find the Sundaras to be a jack-of-all-trades while all the others are masters of a particular one (e.g. the 6xxs are unbeatable in the voices, the 990 in the dynamics, the Grados are best for rock...).
I normally listen to my music at the desktop from hi-res files via Topping D10 + Labs Atom or via Aune T1 (DAC + Amp). I find both options very good. I also use portable DAPs/iPhone or the MacBook Air via the Fiio E10K DAC/amp when I grab the MSR7s. I do not find significant differences when using any of them.
However I noted that the Sundara sound significantly better with the Topping/Atom and with the Aune T1 than when using the Fiio E10k. And it made me think whether their sound could significantly improve If I had a higher-end DAC.
Could you please tell me your opinion about this?. And also how you find the Sundaras in comparison with the 4xxs?. I owned the 4xxs as well and my memory is that their soundstage was bigger than the Sundaras. However I ended up selling them because I found them a little bit cold and distant, with muffled voices, unlike the Sundaras.
Thanks in advance for your courtesy and attention.
Kind regards
Jose Pedro
Artismo
461
Apr 24, 2020
JosepfeSo there will be two or more schools of thought on this: a properly engineered DAC will sound identical to any other properly engineered DAC, or DACs sound signatures vary based on which chip is used and how it is implemented.
For me, I always ask myself these questions:
- does the sound convert the 1s and 0s the way I predict or expect? (SNR, MQA, etc.)
- does it have all the features, outputs, and inputs I want? (Parametric EQ, proper output voltage, XLR, coaxial, Bluetooth, etc.)
- does the DAC incorporate into my system and usage now? (How well the DAC works with my music delivery software or music files of choice, its redundancy and necessity, aesthetic balance, appropriateness for amplifier/speakers/headphone, etc.)
- if it is expensive, is it something I can see myself being satisfied with for a long time and if not, can I resell it at a good value to recoup my costs? (cost to performance ratio)
- why do I want this and will I be satisfied?
axtran
59
Aug 12, 2018
checkVerified Buyer
This is the third O2 amplifier that I've purchased. The other two are made by JDS Labs (one gifted to my brother, one brought to my office at work to spread the love) and this one being the first shot at the Massdrop version. I have to admit that I like the JDS Labs case a lot--it's wider than the Massdrop O2, and you can get it custom laser printed.
That shouldn't really deter most people, though, as the JDS Labs O2 costs more, and performs exactly the same. What I've purchased here is the O2 "Desktop Edition" from Massdrop--slight modifications done without tweaking the PCB. I took mine apart, as I also purchased batteries to install into the amplifier. The work inside is clean and done appropriately--I see no problems with build quality. Some people complain about the power supply--but it works great for my use at home.
Funny part is that I have the O2 Amplifier sitting right by my more expensive amplifier, an Audio-GD Master 9. I'm not comparing the two--there's a huge price difference. However, the Massdrop O2 doesn't bake my room under prolonged use. Paired with a Starting Point Systems DAC 3, my choice of the 2.5/6.5 gain option is enough to drive my most difficult of headphones (Fostex T50 mods, DT990 Premiums, T1s).
If you're looking for something that should fulfill your needs, just pick this up and match is to your favorite DAC. You won't be disappointed. It really is clear, objective, and a quality amplifier as a great price.
That shouldn't really deter most people, though, as the JDS Labs O2 costs more, and performs exactly the same. What I've purchased here is the O2 "Desktop Edition" from Massdrop--slight modifications done without tweaking the PCB. I took mine apart, as I also purchased batteries to install into the amplifier. The work inside is clean and done appropriately--I see no problems with build quality. Some people complain about the power supply--but it works great for my use at home.
Funny part is that I have the O2 Amplifier sitting right by my more expensive amplifier, an Audio-GD Master 9. I'm not comparing the two--there's a huge price difference. However, the Massdrop O2 doesn't bake my room under prolonged use. Paired with a Starting Point Systems DAC 3, my choice of the 2.5/6.5 gain option is enough to drive my most difficult of headphones (Fostex T50 mods, DT990 Premiums, T1s).
If you're looking for something that should fulfill your needs, just pick this up and match is to your favorite DAC. You won't be disappointed. It really is clear, objective, and a quality amplifier as a great price.
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First, about those stars; I gave 5 because, at this price point, this amp does what it's supposed to do, and it does it better than the cost for the amp would suggest. It outperforms expectations for the price-point of the device.
THIS AMP IS A LITTLE POWERHOUSE!!! Listening with my Beyerdynamics DT880 600ohm cans.... Even on LOW gain setting, it runs them well, with no distortion or dropout, on medium volume setting. Thus far, BEAUTIFUL and detailed sound. (REMEMBER, adequacy of power from an amp isn't just about how loud, but also about how clean and correct!) It's well built and has a clean interface, solid but not overly heavy. Cables don't just drag it off the table. This is getting ready to kick the Schiit Fulla2 that I own to my living room......
First impressions; as already mentioned, I love the build quality of this powerful little amplifier. It's assembled VERY well, and the layout of the buttons and knobs etc. is very comfortable and easy to manage, even in the dark when reaching above one's head. It's GOOD that the gain button is adjacent to the volume knob, for instance. I PREFER MATTE FINISHES. I rather hate fingerprint magnets, the urge to compulsively polish shiny surfaces of smudges kind of messes with some of the joy, if you catch my drift. And then I hesitate to touch the thing again....okay enough about it, but, YOU KNOW. First cans, and I chose to review it vs. the Schiit Fulla, as the Fulla, I think, is representative of the amp class and in a similar cost bracket, with similar user purposing. Kind of Music chosen; (Yes, you've seen this list before, because it's THE SAME LIST I ALWAYS USE),Lots of classical with much strings, voice, Beethoven through Bernstein and Glass. Lots of electronic music a la Wollo, Boddy, Roach, Serrie, etc. Much Leo Kottke guitar happiness, with some Bluegrass and Appalachian schtuff tossed in. Classical piano. Silk Road Ensemble. Popular and Rock, from Joplin to Foo Fighters to Neil Young to classic Santana, to The Killers to Maroon 5 and so on. Jazz and Blues , Muddy Waters, early Severin, Puente. I don't really do Rap, Dub, or Hip-Hop, although I did run a little Black Eyed Peas and Outkast through it. My musics were chosen to represent the spectrum and check out what this Amp offers in the way of clarity, speed, presentation of details and ability to translate input from my iPad and iPhone. (NOT from a computer, as there is no DAC.) The Cans; I chose the Fostex X Massdrop THX00 mahogany and the Beyerdynamic DT880 600 ohms. I could actually stop with these, (but I don't want to), because this rather represents the range of drive power required, and two distinctly DIFFERENT sound signatures. Nearly OPPOSITE, although I did choose these Fostex because they tend to be a tad more neutral and the tweek a'la Massdrop was to tame the bass a bit. RIGHT AWAY- the Fostex were very pleasantly served by the O2 on the first day, the easy presentation and tonality we love in our Fostex was handily managed by the O2. Ran them on low gain setting, as high gain is a) definitely unnecessary, and b) was kind of blaring and harsh when the cans were overpowered. (EXPECTED) Day 2, mounted the 880's on it,(couldn't wait any longer), and was IMMEDIATELY impressed by how easily these 600 ohm cans were managed by the O2, EVEN ON LOW GAIN. Detail, which is what I love with BeyerD's, was absolutely present through the frequency ranges, vocals were CLEAR, strings, percussion, all lucidly presented without anything being noteable as harsh or strident. Lovely transparency! And on the 880's detail only became MORE with high gain setting, again, not presented harshly or inappropriately balanced in any way. I can honestly state, especially given my PERSONAL preferences in music listening, that this is producing a very transparent and authoritative sound, and that's before my 30-hour run-in had been managed. I'm not going to say anything silly about stage or headspace, etc. as I believe that's what the headphones do...as long as the amplifier meets the power need of the cans. The Fostex were not overwhelmed, the 600 ohm 880's were not under-served, not even remotely. As I have already said, you can even power the 880's on low gain and lot lose really much. High gain only enhances clarity. Oh, and before I forget- let me mention SPEED, just a bit here. This is a FAST little amp. Something that i feel shines out with the sequencer music heard in pieces by Klaus Schultz, Ian Boddy, and the like. NEVER ONCE, did I feel like I was hearing any drops of anything from musics that I am quite familiar with. Not at any range, not with any genre. Can hear finger squeaks on strings, for instance, intakes of breath. Nothing incorrectly attenuated, EVER, even on harder to drive headphones...always adequate headroom and detail. And we have to admit that 600 ohms is DEFINITELY in the harder to drive end of things. VS The Fulla; The Fulla, being quite nice it it's own right, is simply outshone by the O2. Not quite as fast, definitely not as powerful. The Fostex do not present quite as cleanly, the 880's do not sound as crisp. Volume adjustment when playing the 880's needs to be MUCH higher, nearly at 3/4 for everything to be audible that is audible with the O2 on low gain setting at 1/2. The O2 features a gain switcher, the Fulla does not. Fulla is input to a 3.5 jack, I went with the O2 desktop model which employs RCAs....which I believe always improves the input sound quality because it's just MORE electron flow available, less impedance at the input, less risk of crosstalk. So there's THAT....... In any case, I can say that I already prefer this amp to the Fulla, although the Fulla is definitely more portable with a slightly smaller footprint and a bit less finicky inputting. I wouldn't strap either of them to my iPhone. Coming in Part 2; A few more headphones. ..probably not necessary, but maybe helpful for those newer-to-the-audiophile world who have different cans and might want more information. Something to help with decisions or just understanding what we are talking about with specific equipments.
Hoping this helps ANYONE, or is, at least, a decent read.... cheers! PART 2 ADDENDUM, with a couple more headphones now included; So, I have been messing about with a couple of other sets of headphones on this happy little amplifier, and, as mentioned above, I will now add them to the original.
Let's start with a Massdrop offering, the Massdrop X Hifiman 4XX magnaplanar. As a magnaplanar headphone, while the impedance is fairly low, they can be rather demanding as far as power needed to drive them optimally. The 4XX cans have a rather nice V-shaped sound signature, so a tube amplifier isn't necessary to produce a warm sound from these,(but it doesn't always hurt, either), and a solid state amp can be just the thing. After listening to the 4XX on this amp, I was very impressed with how well they were powered by this little amp, even on the lower gain setting... the higher gain setting did not muddy the sound, just gave a more forward presentation of the lower end.The highs and mids are nicely revealed and clean sounding here. All-in-all, a happy presentation of the musics listened to. As a frame of reference, the HE560's also sound pretty good here, but my feeling was that they want just a tad more powerful an amp to really serve them correctly. They may well be the upper boundary of HiFiman cans with this amp. The Element by JDS Labs sounds better, IMO.
I don't own the Sennheiser 6XX Massdrop offering, but I DO own the Sennheiser HD600, which is one of my favourite headphones for listening to classical, jazz, and acoustic musics. They are a 300 ohm impedance set of cans, so will challenge any desktop amp to serve them correctly. (se above note in bold about how I define that.) I am pleased to say that my Senns sound very nice on this amp. The HD600 is known for its rather neutral, clean, nearly critical sound sig, yet retains intimacy and warmth because the bass is still present and cleanly represented. An appropriate amp will allow these properties to present themselves, even to shine...and the Objective 2 amplifier does its job well here. I won't say that one is at risk for overpowering these cans with it, yet, if it can power those Beyerdynamics 600ohm 'phones, it's not likely to fail the Senns....and it doesn't. I felt the intimacy and natural spaciousness of the Senns when kicked back for a listen- a special favourite here was the Stan Getz-Joao Gilberto collaboration*, which has plenty of sultry-soft vocals and breezy jazz instrumentals covering the full range. It's a must listen for audiophiles, and this amp justified the Senns nicely. I think the Massdrop-Sennheiser 6XX will probably do as well with the O2 amp.
Grado, for those of you who own them; You'll be FINE. I own multiple Grados, and they ALL sound good on this amp, very, well... Grado-y. Nothing robbed or inappropriately nuanced by this amp, yet I tend to run my Grados from my Schiit gear, as I kind of prefer the ss of that combo. I think it's purely subjective on my part.
Okay, that's it for my addendum PART 2 of the review. If anybody has a specific headphone they want remarks upon, and I have experience of it, reply and I'll do my best. :)
* will be added to my test list of listens for any gear I am reviewing.