JDS Labs Assembled Objective2 Headphone Amplifier


New Head-Fier
Pros: Has power, it is almost without distortion (if you can hear any), it's attractive and compact, and the DAC is clear.
Cons: Only found this: the gain of the O2 is not so high, ask JDLabs that they send your amplifier with higher gain. Some high impedance phones lack punch. But this is no hardship. Their other models have more gain.
I came upon the article by the navguy and almost instantly ordered a kit. I was amazed at the sound of the kit, so later I ordered one O2+dac. I am an electronic technician, so I have assembled and purchased many headphone amplifiers and after testing many I am convinced that this O2, the concept of Navguy, is one of the best amplifiers in the market. You can also try the Cmoybb to hear a good bass and the clear sound will amaze you. I recommend these products to everyone. Period.


100+ Head-Fier
Pros: Price-to-performance, transparency, custom options
Cons: A bit "boring" by nature
Meant to be married to the OL DAC, the O2 headphone amp matches it in shape, size and simplicity. What’s neat about the O2 is that JDS Labs allows for some simple customizations—you can choose the headphone jack size (3.5mm or ¼”), input type (RCA or 3.5mm), gain levels, and power jack location (front or rear panel), and whether to have it with or without a built-in DAC and lithium batteries for portable use. I went with a rear-mounted power jack and RCA input, so my front panel is nice and simple with just the power button, headphone jack, volume knob, gain button and a red LED power indicator (why red instead of green to match the OL DAC? I don’t know, but it kind of bothers my OCD).

So how’s the little black box sound? Well, it follows the open source amplifier design from the aforementioned NwAvGuy. In other words, it targets benchmark performance at a budget cost ($129). So, much like the OL DAC, the O2 amp aims for transparency. Or maybe a better way to put it is simplicity. 

For those of you that are used to colored amps, there’s nothing romantic about the O2. In fact, it’s likely to come off as a bit dry, a bit sterile, a bit, well, boring, just like the OL DAC. That is, unless your DAC is colored in another way. After all, all the O2 really does is amplify the signal in front of it, which means a great recording, a nice DAC and a stellar sounding headphone or IEM is what’s needed to put you on the path to #AudioNirvana.

The best thing about the O2, sonically speaking, is its versatility. It has the power and dynamic range to drive anything from a sensitive IEM to a power hungry dynamic headphone with authority. The semi-picky Sennheiser HD650, for example, gets plenty loud and hits with modest authority in high-gain mode. The O2 can also play any genre of music well, because, well, you’re hearing the music and the rest of your equipment for what it is. The caveat here is that you need to plan for this. Meaning, the O2 is going to do absolutely nothing to hide poor recordings, and if you favor a darker, warmer sound signature, you’ll want to choose a headphone with those characteristics rather than something analytical like the reference level AKG K701. Or, you could always dabble with some EQ software to fine tune your setup. 

With the OL/O2 combo, which is what I assume a lot of you reading this review are considering purchasing, you’re getting a pair of neutral performers, nothing more, nothing less. This stack isn’t going to romanticize your music collection. Rather, it’s going to allow you to focus on the music and hone your efforts on choosing the IEM or headphone that best suits your musical taste. 

I’ve mainly been running the rounds with the Audioquest NighthawkBeyerdynamic Amiron HomeMeze Audio 99 Classics and Sennheiser HD650. The OL/O2 drives each of these headphones with ease and enjoyment, although none come off as being quite as airy, lush or three-dimensional as when pushed with a powerful tube amp (just my personal preference), the warm characteristics of each is conveyed cleanly and with good. Although these are all darker sounding headphone, I liked the pairings because it brought some balance to the neutrality of the OL/O2 stack. The consistent instrument separation and detail retrieval of the OL/O2 pairing is solid. The sound stage is modest, extending maybe three to four inches out around the head. Stereo imaging is dead center, although I do selfishly lust for a more holographic presentation. As someone who favors really lush sounding gear, this little stack can sound a bit flat to my ears—bass notes hit with impact, but often lack resonance; mids are clear, but are light on warmth; treble is crisp and detailed, and never too brittle, but airiness and texture seem overly controlled. But all of this is inherent in neutral, transparent solid state amps and DACs. Boring can also be better; the neutrality of this combo makes it an excellent setup for audio purists and gear reviewers because it reveals more accurately what a particular recording, headphone or IEM can and cannot do. 

Overall, I generalize the OL/O2 stack as being crisp, clear, controlled and consistent. Sure, it can be boring for those that favor the ooey gooey goodness of lush and distorted tube gear, but boring isn’t always bad. In fact, these little black boxes are probably one of the best places to start for new budget-minded audiophiles looking to learn just what it is they like and lust for. 
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Wow, really awesome review!
I have been looking around for these sort of reviews as this is what I am looking into buying.
I'm really debating between Modi Multibit + Magni 2 Uber or ODAC/Amp or Modi Multibit + O2Amp or E18K for now
Thanks for reading @Jimster480 ... The Modi/Magni and OL/O2 are very similar in price and specs. Honestly, you can't really go "wrong" with either one. I'd look more at which one provides all the inputs you need and which suits your price point better. After you run either the JDS or Schiit for a while, you'll have a good feeling for what sort of sound you want to go after next, if you even need a next. Good luck!
Thanks @SoundApprentice!

The Modi Multibit is $250 by itself though and I would need a Magni 2 Uber which brings the cost of the stack to around $400 vs $250-300 for a OL/o2 stack.


New Head-Fier
Pros: Sounds Great
Cons: Not super small
I read about this device online and the reviews were very positive - so positive that I jumped in.  It was my first headphone amp — I purchased my second, the fiio a5, shortly afterwards.
Take into consideration I am an amateur audio geek...
It is just what everyone says about it; zero background noise; clean sound; no extra color.  I did also read that it was a little on the large size to be considered portable, and I agree that it is.  However it will fit in the back pocket of my Levi's so I'm still considering it portable.
After comparing it to the fiio a5 for a week I must say I prefer the Objective2.  The "uncolored" sound is really more my style.  I wasn't sure where I fell on that spectrum...  But after comparing, I get it.  The objective2 is cleaner, more open.  You are not going to find something like a tube amp warmth.  But what you will find is your really great recordings in crystal clarity.
Physically it's a nice solid piece of equipment.  It has a single red light when it's on.  The battery power so far seems to be in line with how it's advertised.  I do like that I can replace the batteries easily if I needed to.  Little things like that make this a special piece of equipment.  The volume control has a wide range so you can adjust it to very specific levels.  JDS labs has responded to my queries in almost real time.  They are very friendly and accessible.
I currently own the (Fiio E12) and was considering an upgrade or wondering if I should get a desktop amp and keep my E12 strapped on my X5ii, and I was considering either the Objective 2 or the newer A5. I thought the A5 was totaly neutral too as it's what also the reviews and benchmark were showing. The O2 have a bigger soundstage and even more clarity? The specs of the A5 seems better though O_o


New Head-Fier
Pros: Size, performance, facilities(custom model)
Cons: None
I bought this to listen to my vinyl on my Hifiman HE-400 phones.  It does a great job of driving them with a very neutral and I can hear detail that my £5500 worth of amp and speakers don't pick up.  The JDS Labs would cost $191 shipped to the UK.  I bought a really nice version from a UK based eBay supplier (macwidow2011) - Swiss made board, neutrik connections, ALPS pot, RCA inputs and outputs with 1/4" jack - all for £109 shipped. 
Sonic Defender
Sonic Defender
Your speaker system is picking up that detail, unless it is quite old. The difference is that headphones are right on your ears so quiet details lost when sitting feet away from a speaker are easy to detect.


100+ Head-Fier
Pros: value, clarity, small footprint, runs cool, reliable, can drive many headphones
Cons: could have more power for harder to drive headphones, could have more modern design, could use few other updates to bring this little Tarzan into 2017
You know that feeling when you wake up in the morning and you can smell the coffee (Columbian, beautiful like their women), bagels (plain but fresh no manager specials) being toasted and birds singing (bunch of them in perfect harmony). It's the feeling of life just being right and problems being thing of past. That's how I feel today so I thought let's write a long overdue review of this little wonder called Objective2 headphone amp. There are many reviews with detailed numbers and measurements but my review is just my opinion based on many hours of listening all type of music with different headphones.
My unit was purchased used for only $55 shipped here at head-fi few months ago. This is my second O2 amp first one was a JDS my current one is Massdrop made in China. Don't let the price tag fool you this little amp can't be beat for the money spent compared to amps costing much more. I had amps up to $2000 and unless your trying to power Hifiman 6 or certain planars your search can end right here right now. Do not waste your money do not fall for the hype because only hype real is the Objective 2 hype and that hype is real backed by measurements and cult like following over past few years.
What makes O2 special is that it's a neutral amp (wire with gain as we call it) and it does not change the flavor of the sound . That is exactly how amps should be and rest of the gear so you can enjoy the soundtrack the way it was recorded in the studio and listen to headphones the way they were designed with their own sound signature. This little Tarzan has good power and is able to make most headphones sing including HD600, HD650, Beyer T1 (600ohm but fairly efficient). 
Now is there a better amp out there? Yes, of course but requires you to spend at least six times of O2 price tag. While powerful, this little Tarzan could use slightly more power since I find some of my headphones slightly lacking in the lower frequencies but we are talking about very small improvements that takes good ear to evaluate.
For money O2 is a slam dunk and one of most popular amps of all time for a good and well deserved reason. If you are trying to get your feet wet or just trying to find your final amp O2 will not disappoint most of audiophiles.
Now back to last sip of coffee....  refill time. Let's load up on some more bagels. Oh snap, I'm out of cream cheese.
If you find my review informative and fun please take quick moment and sub to my youtube channel:


100+ Head-Fier
Pros: Ability to build yourself, modification options, case engraving, customer support
Cons: Would love for the LED to indicate low battery/charging
You've already heard that the sound quality of this amp does not match its (low) asking price. You already know that it's one of the best SS desktop headphone amps you can get for your cans at any price point, really. So why am I writing another review on an amp that you KNOW is going to be awesome? Well, my review is for those who like to build their own amps and JDS labs is a company that "gets" the DIY movement and have made NwAvGuy's design really easy to build for those of us who like to roll our own gear. My review is meant for those who might be interested in ordering a DIY kit but who might not be sure of what they're going to get:
Remember back in the day with the O2 was new and there were people scrambling to put together Group Buys for PBCs and components? Well, those days are OVER, thanks to JDS Labs!
All the components come in their own plastic baggies, labeled clearly so you know where they go on the PCB. The PCB itself is of the highest quality you can expect as are the components themselves. All op amps and mosfets come in sealed anti static bags. For me, this kind of kit is a dream - I don't have a lot of time (or patience) to wait for people to put together Group Buys for an amp like this to save a few bucks. You would think that JDS labs would be marking up the cost of the DIY kit for this convenience, but frankly, they deserve a lot of credit for being able to provide the DIY kit for this amp for almost as much as it would cost you to go and buy the parts at a local electronics store, so the small "up charge" that you're going to pay isn't much at all when you consider how much time you're saving if you were to decide to spend a few days gathering the components yourself (and it might actually cost you more considering shipping charges and/or gas).
I built mine using Cardas quad eutectic solder (the ones JDS sells are built using lead-free solder). I'm sure lead-free solder is fine, it's just my own personal preference to use quad eutectic solder for all my builds (and that's the nice thing, isn't it? You can use whatever solder or equivalent components of your choice for builds like these if the ones included aren't to your liking). It took me about 3.5 hours to put together the kit (PCB board and components, $60 at the time of this review). 
At the time of this writing, there are no detailed instructions on how to put the kit together yourself on JDS Labs' website, but you don't need any really. Everything is labeled on the PCB itself, and everything is separated and labeled in baggies for you. There is however, help on their site for the various mods you can do (gain, RCA connectors, rear power, etc.) You do need to know how to install components for a build like this (like knowing which is the positive lead on a capacitor and which is pin 1 on an op amp, etc.) Adequate soldering skills are also necessary and I highly recommend a variable control soldering station for this kind of build too.
JDS Labs' customer service is excellent. I've received responses to emails within a short amount of time and I've got nothing but great vibes from them with each response. Although I didn't have any questions concerning the build itself, they have been very responsive and helpful. I ordered an enclosure from them which I later decided to get laser engraved and they've been very helpful in answering file format questions, I'm sure if you have any issues with their kits that they'll be just as helpful.
I'm so happy with my kit and interactions with JDS Labs over this Objective 2 that I'm going to be ordering more kits to build soon!
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Hal X

100+ Head-Fier
Pros: (in my case I bought the kit)DIY. Perfect. Just the perfect wire-amp with no coloration or issues.
Cons: None
I own the desktop version of the O2. What to say? It is just perfect in every sense. No coloration , no noise, great power, best tecnicalities out there. BEST VALUE EVER. Endgame amp.

YoYo JoKeR

100+ Head-Fier
Pros: Sound Quality, Build Quality, Customization, Value
Cons: Portability Issues
The Objective2 is my first amp along with my beloved HD600 headphones. Here is my review after my experience with it for several months.
Intro : I am an 21 year old Engineering student living in a small town in India. There is not much audiophile-community presence in India, Though lot of potential remains to be tapped. Auditioning an amplifier before purchase is almost impossible in India.
I would like to call myself an music enthusiast, rather than an audiophile. I mostly listen to Bollywood and Indian Classical Music.
I had bought off the O2 amp solely based upon its reputation, and also because of not being left with enough funds buy an more feasible amp.
The O2 amp is designed by an famous American electrical engineer. It is well documented and measured amplifier, leaving no second thoughts on its performance. The goal of O2 amp is to achieve transparent sound with good measurements and at a reasonable price point, So that every enthusiast could afford an decent amplifier.
The O2 can also be customized easily. It is available as a kit, or readily assembled, with/without case. It is cost effective and has many more add-on options.
Design and Build : It is an very well designed and built amp. All components are mounted on an single PCB, with no manual wiring, which ensures longer life. It consists high quality double sided PCB, passive components, semiconductors and an Alps potentiometer. Exterior case has equally good build, with finished anodized and brushed aluminium case. Front and back panels are mounted by 4 screws, which can be removed easily to slide out the O2 board. All controls and jacks are mounted on front panel of O2.
Overall,The O2 amp has Excellent build quality and design. Cant ask for more from an DIY amp.
Sound :  O2 is very transparent. It has no ‘sound signature’ of its own. The output from the O2 depends very much on the source and ultimately on the headphone you are listening; it’s a wire with gain. It is an reference amp in sub 200$ price category, and comfortably competes with amps which costs much more.
The O2 amplifies the input signals without adding any flavour of its own, which results in improved soundstage, dynamics and imaging. This transparent sonic character makes the O2 amp suitable for any genre of music. O2 has zero audible background noise and pitch black background. It has a very low EMI pickup, which is an advantage for Smartphone users.
Output Power: Specifications state that O2’s output power is sufficient for most of the headphones. O2 amp can drive both dynamic and planar-magnetic headphones, though the latter seems much difficult to drive; The O2 takes the dynamic HD600 and planar magnetic LCD2  to loud listening levels, but ultimately lacks dynamics and power to ‘drive’ them properly.
We know that the O2 can have custom gain settings. Though by default, the O2 comes with 2.5X/6.5X gain. Once the gain is flipped to 6.5X, background noise and distortion increases. I feel the gain switch is best set at 2.5X. But this again limits the O2’s output power for demanding headphones.
The O2 amp has low output impedance and is hence is also suitable for IEM’s and earphones. One can hear an small ‘pop’ noise from headphones when O2 is switched on/off.
Portability : The O2 amp is not sleek or light as the Cayin C5 or FiiO E12. The O2 is more of an transportable amp than truly portable.The O2 amp can work either on Internal Rechargeable 2X 9V Batteries or on External 15-20 VAC Adapter.
Once fully charged, The O2 works on battery power for around 6-8 hours, which is quite decent. It doesn’t have any audible differences when running  on batteries or on AC Adapter.
Slow recharging process in implemented in-order to avoid over-charging the batteries. Once the AC Adapter is connected to the amp, the battery recharging process is initiated. It takes around 12 hours to fully recharge the O2. There is no indication to the level of charge in the batteries; we have to manually estimate the approximate battery life remaining.
Most of the portable amplifiers use 5V USB Charging. Whereas O2's AC Adapter is heavy, and is cumbersome to carry around. This further limits the O2’s portability.
Though O2 is an excellent amp, but It's portability side suffers. If one wants to sacrifice the transparency of O2 for better portability, CAYIN C5 and FiiO E12  are pretty good amps, which have higher output power and are truly portable, along with very good sonic quality.
Conclusion :
The Objective2 is an fantastic amp, It is hard to beat O2 amp in its own category. O2 is an easy recommendation for an budget amp. Though not very portable, the Objective2 does its job and does it very well.
The following features make O2 amp unique amongst others :
1) Transparent Sonic Character
2) Battery/Adapter operation
3) DIY and customization
4) Decent output power
5) Easy maintenance
6) Transportable
7) Affordable.
O2 is like an transparent window, which shows us, the view into music.
My SennHD600 lack punch with the O2. I followed the instructions and changed the 4 gain resistors to very high gain. If you hear scratching or noise you can correct it by lowering the volume. The amplifier is powerful! I like to have extra power because it makes me feel that I can control the music when needed. If you want to know more you can contact me. Look at the instructions manual and consult the gain. When I was 15 years old every device used tubes. We had no problem with that.


Headphoneus Supremus
Pros: Light, Gain Switch, Replaceable Battery
Cons: Not Lithium Batteries for More Power or Run Time
I've been reading so many replies and reviews how the O2, Magni and Vali sound the same. After weeks of listening to all of them, (yes I have them all) they are all not exactly the same . I've been using the same music and all else in the system is the same and have only changed the amps. Started with O2, then went to Magni. Yes the Magni and O2 sound very close. The Magni does sound a tad processed and thin compared to O2 but the Magni does have more authority as it is more powerful in comparison even though they all seem to struggle reproducing the source. The O2 is a really nice amp but when compared to the Magni the O2 is better overall, but sound wise when compared to Vali in sound the Vali is a tad better.

I hope this helps anyone who maybe interested in the O2.
Update: I would recommend the Aune amp over the O2. Way more resolving, less distortion and is a true Class A amp.
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Thanks for reviewing!
I like that you distinguish the good qualities of the O2 and Magni, do you have a Vali review with details?


New Head-Fier
Pros: Flat sound. tight bass.
Cons: Charging mechanism is pathetic.
It lives upto its name. This ne is a gem as far as neutrality is considered most neautral Amp i have had or tried so far. I have tried HiFi man EF5 Fiio E11, E17 ,little dot mk2 etc. and found them clearly sub par comparing the bar this product has raised for its price. The immediate this one can notice is great improvement in both treble and Bass. Bass is quite tight. Treble is cold and accurate. Might sound little harsh for headphones like ATH50 but suits well enough for HD650. Wanted to try out well known tube amps especially Schiit Valhalla, Bravo audio ocean and the HD650 specialist (as per many folks on forums) Bottlehead crack. Unfortunately they are not easy to find in the part of the world i live. and i am not much into DIY either.May be someday i'll get my hands on them and then compare the famous tube sound signature with this little beast's accuracy in terms of SQ and see what suits my ears more, accuracy or the warmish (yet close to accurate) sound. For now i'd safely say this is best in class Amp and a great value.
Let's look at its shortcomings.
1. the charging mechanism has not LED indicator to show whether charge is full or not or whether it's charging or not for that matter. It  gets really annoying that i have to keep it off while it's charging and yet i don't know whether it is actually charging. It in fact most of the times is charging unless the heavy adapter has lose connection(it is quite possible as the adapter weighs more than O2 itself.)  or you forget to switch the button on (like i have done couple of times :p)For a 130$ product this wasn't a big feature to ask. 
2. Gain switch is useless IMO as it totally screws SQ I never needed it though, HD650 can get enough juice on 2.5X gain setting. 


New Head-Fier
Pros: Fantastic sound to price ratio after modifying, Very versatile for modding - spacious boards, easy op-amp rolling.
Cons: short battery life (8-9 hours), long charge time (12 hrs using 18V ac, 770mA), audio quality becomes source dependent. Not very portable.
This is my first review submission for head-fi, hope that it could provide some comparison and enough information to let you decide whether to make a buy for it. But do remember this review is from my point of view and the ultimate decision is down to your ears to decide.
Tips for mods and results of modding are listed at the bottom of the page. Do note that modding the O2 is done at your own risk, Don't hold me accountable and say you've blown your capacitors because opamp is inserted wrongly or the rating does not match.
(Any opamp that operates at 18V should work fine, including some that states 12,15,18V etc. Basically as long as you see 18V it should pose no threat.) I've not tried opamps that don't operate at 18V yet, so please do so at your own risk (Really not recommended too). I also did not try the OPA 627 because it is expensive and pin configuration of a mono opamp seemed different from a stereo opamp, meaning it is not a direct drop in. Correct me if I am wrong though. Again, do this at your own risk.
PS: My O2 is 4-5 years old, any new revisions to the PCB are not known to me. I'm basing my review on the earlier generation's O2 that does not offer the 1/4" jack yet.
Some prologue of my sound preference (as a reference) (edit 03/2017):
I realised that I'm a tube person after playing this hobby for some time, and my reference sound signature is my Aune T1 tube dac (Using Voskhod rockets 6N23P) to TU8200 tube amp (Using NOS Matsu****a 12AU7 and reissue Goldlion KT88s) driving Grado SR 125i, T50RP MK3 and MDR7506 modded with Kimber cables. Vocals are my favourite along with well balanced overall sound. Full sounding, well detailed, good separation, vocal depth, image depth and staging that is in front of you (not on top of you or so). All audio frequency should complement each other, not fight against each other, forming the gateway to heavens when you close your eyes to indulge. Lastly, I believe music should come to you, instead of you trying to look for music while listening. This point is hard to explain but I hope the meaning went through lol!

First few things to start off with here that I believe will be important:
I view this product more as a portable equipment instead of a desktop appliance. Therefore my comparisons are usually made against portable amplifiers. 
The sound of O2 depends greatly on the source.
The fact that O2 is a very neutral amplifier makes it reliant on the DAC and the file formats it is using.
For instance, using the DX50* as line out vs. using DX100* as line out, the difference is greatly noticeable.
In another instance, my friend tried my O2 using his phone as a source. He didn't like the sound he's hearing until I changed the source to DX50, where the overall dynamics were improved.
*DX50 is running Firmware1.2.8, DX100 is running FW 1.2.7. Both DAPs are using the exact same copy of songs, FLAC quality converted from CD.
Comparing O2 with other amplifiers:
I have the Aune T1 with modded capacitors at the amp section, so I decided to compare the T1's modded amp section vs the O2.
The O2 has a tiny bit less bass punch, lesser 3D vocal depth and sounds slightly less engaging. The highs have not much noticeable difference, probably due to the headphones i'm using.
Source used in this test is in FLAC format using the Aune T1 as a DAC for both amplifiers. The tube on T1 is a NOS Philips JAN 6DJ8. LO cable silver RCA-3.5mm for the O2. Headphones used is Custom One Pro.
I've also bought a second hand DX100 v1.2.7 recently and changed the batteries in them, and did a comparison of DX100 on board amp vs my O2 modded amp. O2 had a n[size=1em]oticeably more refined and slightly broader soundstage, slightly darker background, instruments separated much better, more natural vocals though it lost a little vocal depth (still more than acceptable imo) when compared to DX100. Volume is adjusted as equal as possible in the vocal region for fair comparison. Anything else to complain is probably the digital steps of DX100 compared to the easier analog control of O2. Winner here is undecided as it's hard to consider if I should bring a big brick or a bigger stack, whether is it justifiable for the slight improvement in sound. Comparison done using T50RP MK3 and 24/96 FLAC songs.[/size]
(Edit 03/2017:) Recently I bought a second hand DX200 at a good price :D and compared the amp1 output to O2. Tried it on T50RP MK3. In short the most obvious difference is that O2 is slightly cleaner and less bassy than the DX200 but much better bass control. Low frequency separation is more noticeable and defined than the DX200's. I will do another update after I have done sufficient comparison. Stay tuned!
Have not tried comparing this with Cayin N5, may do so in near future.
[size=1em]Do not bother to ask me how it sounds compared to my TU8200 Tube amp as it is too unfair to do so. The magical sound pixie inside a vacuum tube is mocking at the opamp transistor now.[/size]
Stock O2 sound signature:
1) O2 is fast and does not smudge the song when playing fast songs.
2) Neutral, it literally only amplifies the source signal.
3) It is suitable for almost any genre songs IMO and generally presents the music with a better soundstage and imaging without changing how the music sounds like.
4) Due to its neutral nature, some may not like the sound of it as it may make a song sound a little boring and slightly less dynamic compared to portable tube amps.
5) The ability for micro details to be picked up is more source dependent. But O2 does a good job on the micro details, making sure they don't get left out.
1) Good volume knob, quite strong and can withstand some abuse. No hiss produced when turning the knob.
2) Strong aluminium case to keep internals protected and at the same time would not be too heavy.
3) All the plugs are located at the front panel, which may be good and bad depending on how you use it.
4) When the amp is switched on, only a tiny pop sound can be heard. (no pop for my modified O2)
5) The stock O2 makes the instrument separation, imaging and staging better without tainting the sound.
6) Only 1 circuit board present in the amp, making the configuration a lot easier to be understood (for people who like to mod)
7) Current limiting stock op amps used at output to protect expensive IEMs.
8) Very powerful (up to 613mW into 33 ohms on battery), stock opamp config. 
9) Battery can be changed out when it runs out of juice. Rechargable batteries can be changed when it ages too.
10) Not very space taking if compared to other desktop amps.
11) Very versatile for modding.
12) Good sound performance to price ratio; you get more than what you pay for.
13) Good amp for starters.
14) Stock O2 has nearly inaudible hiss unless you are using CIEMs. Hissing sounds may come from sources instead. However, the opamp can be swapped out to reduce to almost no hiss at all, even when the volume knob is at max.
1) Short battery life - ~8h. ~9.5h after changing to higher capacity batteries.
2) Source dependent. = Need to get a good DAP or DAC
3) Big and bulky, not pocket friendly
4) Stock O2 on high gain sounds horrible. Modded opamps high gain still distorts too greatly till it clips at higher levels. You may want to find NwAvGuy's O2 PCB design to see his design gain stage resistors value and reduce the resistor value for high gain to reduce clipping issues.
5) Certain songs (sources) may sound too neutral and cause it to sound boring
6) Some may not like all the jacks to be at the front panel
Interesting things to share about O2:
Suitable OPamp replacements for O2: JRC(NJM) 2068DD can be replaced with NE5532 or LM4562 according to the O2 blog site.
Edit: Performed experiments with a circle of friends for op amp rolling and the final configuration for O2 is 2x OPA2132PA for the power stage, (the 2 identical chips on the PCB), then a choice of OPA2228PA or AD823AN for the gain stage (the chip near to the volume knob).  The OPA2228PA offers a tube like sound while the AD823AN is the best all rounder for musicality. The O2 is more musical with either new configuration. Optionally, 3 OPA2132PA can be used together. This gives the sweetest sound compared to other amplifiers you can find out in the market, and it may or may not be liked by people. Conclusion: ROLL THE O2 OPAMPS!
Please do note that battery life is influenced by the type of opamp used too. To my experience the OPA2228PA causes the O2 to die faster than other chips I've used.
EDIT#2 (Nov2015): This configuration was used by me for the longest time so i have decided to finalise my configuration and share it. 1x OPA2132PA for gain stage (the chip closer to volume knob) and 2x AD823AN for output stage (the 2 identical chips seen on PCB). The rationale behind the change is because the AD823AN utilises R2R technology and is able to deliver higher current into headphones more efficiently than standard design op amps. That said, don't expect this thing to drive a pair of Alpha Dogs as some headphones are still a little too hard to drive for this amp. (Edit 09/2016: It drives the T50RP Mk3 quite well). Do note that the PA and AN behind the chip numbers are important, otherwise the price of the chips will skyrocket.
Additionally, it is strongly recommended to change the stock batteries to better quality batteries with a larger capacity. It affects the ability of the amp to deliver the current for improved attack and control so your music don't sound bad. I am using 280mAh batteries made in Japan and they last me 9-12 hours fully charged.
O2 can be used as an pre amplifier as it does not change the sound signature much, but it improves the sound stage. Edit#2: Finalised configuration works superb as a preamp, touching up the musicality without colouring the sound.
I hear audible but negligible hiss using my 1964 V2 CIEM with no source connected to the input and volume knob at MAX. It is definitely going to be an audible hiss, but nobody with the right mind will use this amp at max volume to a precious CIEM. With volume knob at 8 o'clock, the amount of hiss will definitely not affect your music.
It would be better to remove the battery if you are using it as a desktop amp. For some reason the sound is different with and without battery mounted.
If you do not like to use the equalizer, then change the interconnect cables to fine tune the sound.
I hope the above review can help!
Please do feel open to PM me for questions regarding op amp rolling for the O2. I'm still active even though I do not post opinions in forums. Will always add on to this review as and when my new equipment comes in.
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New Head-Fier
Pros: Sublime Transparent Sound, Price, Build Quality, Adaptability.
Cons: Maybe could have used the source input & PSU inputs at back

1st things 1st I guess ;
I tip my hat to the Guy who Designed the O2 & to JDS Labs also for making it ready built.
Now I don't know the Guy who came up with this O2 Headphone Amp but if I did I would certainly shake his hand.
I don't say this lightly but here it is then ;
This little Headphone AMP is quite simply put the best sounding Headphone AMP I have ever heard, PERIOD !
You add in the fact that I imported it into the UK direct ready built by JDS Labs for just under £100 including a UK PSU for recharging & I guess that possibly makes this little gem then truly the best value for money Hi-Fi component I own including any full Size Hi-Fi components in my Linn/ Musical Fidelity main Rig.

I normally use this paired with my now favourite cans the Shure SE 535 Ltd red's & all I can say is that it's like I'm listening to my big Hi-Fi System through it's Linn speakers & not through a Headphone AMP/ Cans combo :)
I cannot stress the clarity/ transparency of this little AMP enough, it's just a breath of fresh air in an otherwise "Snakeoil" & Overpriced, Overhyped & quite frankly mostly Junk Headphone Market. If you buy into the "Oh it has to be a brand name for it to sound good & thus cost a plenty style of thinking" then you'll probably never even get to try this little gem as you'll be too busy handing over £1,000 for your branded heap of junk headphone amp that you only bought because you "Like that brand & somehow think that they'll always produce greatness".

I have heard a few shall we say just Higher Priced Headphone AMPS & I won't mention any names as I don't want to even give their brand names any attention whatsoever when I'm talking about the O2 Headphone AMP instead so we'll leave at this statement then regards how it measures up to other Headphone AMPs costing even £1,000+/-'ish range ;
IMHO it wipes the floor with the lot of them !
Sure some maybe have a Remote Control or some maybe claim their made of Diamonddilliam but very very few will even publish their "Data/ Specs/ Info" on their real world performance so read into that what you will.
So performance wise it's hard to beat this little gem.

On practicality etc...
Sure you could use this portable but you'd need big pockets or perhaps even a little bag or backpack if you really wanted to venture into the urban jungle with it.
I personally don't go portable with it since I own a Clorfly C4 Pro & that is an excellent player that needs no amplifier at all as it'll go loud enough to make you deaf :wink:

I use my O2 for tapping into my Living room's Linn/ Musical Fidelity Hi-Fi's Streamer for its Flacs/ Wavs & Inet radio rarely
I use it also for tapping into my bedroom System again a Linn/ Musical Fidelity's Streaming source or again rarely Inet radio.

I guess I should add that I use a Custom made Phono to Mini-Jack Solid Silver Litz Cable a friend made for me especially for this purpose (It's about 3.5Metres Long), I would recommend if your the type who looks for weak links in their Hi-Fi chains then perhaps consider your cable & indeed your cable for your Cans too which is again in my case a Silver Custom job.
I find silver to be very transparent compaired to some of the more expensive options out there.

Back to the O2 ;
I tried it with loads of cans & was never disappointed once, as you pretty much get what you throw into the O2, you give it some trance in 1 side then some nice tight bass comes out the other etc... Didn't find any type of music that it didn't do justice with at all.
I'll say this though, if you throw into it a 128kbps MP3 then that's what you'll get at the other end, so in a nutshell feed it well & you'll be rewarded.

Only downside I see to this is that I do think maybe a little redesign so as the inputs are at the back would be nice & perhaps some1 has now done this, but I prefer sound quality over a small flaw in design any day :)

So to some up then ;
Laughs at the bigger boys & their £500+ AMP's IMHO
Buy 1 as you simply won't be disappointed I promise :)

1 last thing, please no dumb replies with statements of but this £1,000 branded 1 I have is way better as This is just an opinion so don't throw a hissy fit because I think this little gem is great Mkay ? :wink:

I have it, and I disagree.  It sounds considerably worse with my lcd-2 than the burson soloist I demo'd them on.
Being in the UK, you should have looked into the Bushmasters MK2 DAC/AMP. This underexposed box beats out some high-end DAC's for a start and though you pay more than an O2 alone it is on another level to most DAC/AMP combos at "entry-level" prices. There is a thread on here and one in UK and the people who rate it highly have got high-end audio chains as it is.
It beats out the $1k (though older) Benchmark DAC as one example. The headphone amp section by all accounts drives LCD-2s very well.
I love it with IEMs, but with my HE-500 it struggles. 


500+ Head-Fier
Pros: Very accurately reproduces the source signal; I guess it could help if the source's headphone jack isn't strong enough
Cons: Could use more power
The objective facts
Background: I listen to music on a higher-end (purchased for $800) Asus laptop, or my Galaxy Note 2 smartphone. With my SRH940s, the phone sounds better in terms of sound signature, but with my Sennheiser HD800s, the laptop sounds better for some reason. But they're both very close. All of these experiments were done listening to music on Spotify 320kbps; that's how I listen to headphones 99% of the time so that's the only way to test for my purposes.
How I tested this: I connected the O2 amp, with low gain, to my laptop's output jack. I set the volume of the O2 amp to its highest level (in other words, I controlled the volume of the music from my laptop's volume meter). The playback was set at 24bit / 192 khz (basic windows audio lets you pick this option). I plugged the HD800 into the amplifier.
The first thing I noticed was that this setup didn't cause the HD800 to be that much louder than it was when I simply plugged it directly into the laptop. In other words, with the O2 amp's volume set at max, and my laptop volume set at 25%, the headphones had close to the same volume as when I plugged the HD800 directly into my laptop and set the volume to 25%. So my laptop has as much power as this thing. Then I turned up the volume to the maximum and used a decibel meter to see how loud the two could make the headphones, and again, very similar. I repeated the above with the phone and got more or less similar results. 
Subjective observations
Next I cycled through a few songs that are very well recorded, to see if they sound better on one vs. the other. I listened once, twice, three times, again, again, focusing on very specific parts of the song, often playing 10 second portions of a song and repeatedly alternating between the two sources. I could find nothing. I would often focus on one tiny detail in a song, to see if the O2 and computer produce it the same, and they could. When the O2 was driving the phone, it had the phone's less desirable sound signature, and when it was driving the laptop, it had the laptop's sound signature, but the O2 didn't change the sound at all. I thought an amp was supposed to improve the sound of my "power hungry" HD800, but this did nothing. However, commenters say that this is exactly how it's supposed to work. In other words, it's not supposed to change the sound at all. So I guess I can't rate it poorly for doing what it's supposed to do.
Conclusion: If you have a severely underpowered source and need power, this will deliver it. But it could do more in this respect. It's not underpowered like some of those pathetic portable amps you see out there. But in my opinion, a $130 desktop headphone amp should provide boundless power, as much as you could ever want. When you buy a desktop amp, you should no longer be concerned about not having enough power. You should be concerned about keeping the volume low so as not to blow out your ears. To provide technical stats, on its website, it states that the O2 can only deliver a maximum of 88mW at 600 ohms. Well what if you're trying to drive a T1 or another 600 ohm headphone? Is 0.09 of a watt enough? Again, it has power, but you might not need the little bit of extra power this provides, and you might be fine sticking with your laptop or phone's amplifier. In light of the fact that it costs $130 and sits on your desktop, but doesn't have huge bountiful power, I'll subtract 2 stars. I'm just not sure why you would buy this if you want a desktop amp.
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It's just amazing he has a HD800 and does't even use a proper DAC. To be honest it's a useless review. I'm still more surprised you bought a O2 with 0 knowledge...
I wonder If he did get to try the O2 with an external DAC and noticed any improvement over the laptop headphone output
I know this is an older review but it seems his O2 was preconfigured with no-gain. JDSLabs offer O2s with 1x/2.5x gain, which can be readily adjusted by swapping 4 resistors near the gain switch. Yet an amp (be it headphone or speaker one) is supposed to amplify the volume and act as a voltage buffer. Any changes in sound comes from poor PCB layout, noise isolation, feedback, ground loops or were added deliberately by the manufacturer. "Wire with gain" concept of O2 is not supposed to do any of that - it should present the reproduction as neutral as possible.
Setting WASAPI engine to 24/192 won'T magically improve the sound - you should always run the sample rate with consideration to the source files.


100+ Head-Fier
Pros: Neutrality, Definition, Cleanliness (Black Background), Articulation, Speed (PRAT factor), Imaging, Transparency, Power, Value (Price/Performance)
Cons: If you prefer a certain sound signature from an amp, it has no obvious character of its own, therefore it depends on our source and headphone choice
I have always loved the Grado RA1 which uses the high output NJM4556 op amp. It was one of my very first introduction to the world of headphone amping, and for years it was the mainstay of my main listening rig, both desktop and portable. The JDS O2 amplifier is using similar op amp(s) for its output stage ( and doubles it!), thus I found this JDS Labs Objective2 amp to be easily lovable right from the first listen. It does bear a resemblance in sound to the RA1, but it has more definition, cleaner sound, and more power as well.

I had owned a lot of affordable amps: the various CMoys ( I have owned most major CMoy version:JDS, Zigis, Penguin Coffee Amp), 3 Channel PIMETA, Schiit Magni, RSA Shadow, XCan V2, GSP Slee Solo mk2, RA1, PA2V2, Creek OBH11 amp, and Fiio E12, but the time had come to downsize the number of my amps. I sold the others (I need the money to get an iPhone 5S, which is unsubsidized in my country's market) and kept the O2 as my one and only one amp after months of evaluating them side by side. It came down to these three: Schiit Magni, RSA Shadow, and JDS Labs Objective2, and then I picked the O2 out of those three. I haven't regretted my decision ever since;  I very much enjoy listening to Smooth Jazzes, the likes of Lee Ritenour, Earl Klugh, Fourplay, David Benoit, Dave Grusin, Incognito, etc. with this amplifier. It's paired with the following: AKG K702, Audio Technica ATH CKS1000, Philips Fidelio S2, or VSonic GR07 mk2, and also with the ODAC, Rockboxed Sansa ClipZip or the iPod with DIY iMod as the source. I love how the amp effortlessly disappear allowing me to enjoy just the music.  


Headphoneus Supremus
Pros: Excellent sound quality, great price/performance ratio, battery and/or AC powered, adjustable gain options, no background hiss, packs plenty of power
Cons: Everything is on the front-panel, low-volume channel imbalance, too bulky to be used as a portable amp, finicky with TRRS jacks
Without referring to "He-Who-Must-Not-Be-Named's" (A.K.A. NwAvGuy) blog, and speaking from my own listening experiences, I really do think the Objective 2 is a great headphone amplifier. No, I don't think this is the amp to end all amps, but it's a dang good one and it only cost me $156 USD (which includes the Triad brand WAU12-200 AC adaptor). In fact, it can be found even cheaper nowadays from the same vendor, JDS Labs, for $140 (including the same adaptor).
What's in the Package?
  1. JDS Labs Objective 2 headphone amplifier, wrapped in an anti-static bag
  2. 2 removable, rechargeable Tenergy 9 V nickel-metal hydride (Ni-MH) batteries (already installed in the O2)
  3. 4 adhesive clear-rubber feet
  4. 3-foot long Monoprice mini-USB to USB cable, with gold-plated connectors and a ferrite bead
  5. User Manual
  6. JDS Labs business card/contact information
  7. 2-year warranty free of part/manufacturing defects
  8. Triad WAU12-200 AC adaptor (if purchased)
Custom Orders
There are also 3 things you can get customised when your order your O2; all you need to do is fill out the "order notes" section before you make your purchase:
  1. Specify if you want a free custom laser etching (source: http://www.head-fi.org/t/643435/review-jds-labs-o2-black-edition-o2-odac-discussion/345#post_9560679)
  2. Specify if you want an alternative gain option (you can do this yourself by-hand, or JDS Labs can do it for you)
    1. If you do it by hand, you can follow this guide to get 2.5x/1.0x gains, or 1.0x/6.5x: http://www.jdslabs.com/pdf/O2_LowGain.pdf
  3. You should contact JDS Labs before ordering the O2, but it's possible to purchase a larger O2 unit with a 6.3 mm output instead of the standard 3.5 mm one and/or have the option to add RCA inputs for a $10 fee (source: https://www.facebook.com/photo.php?fbid=622772244410229&set=a.347705048583618.85653.213109922043132&type=1&relevant_count=1)
  4. This isn't part of the special "order notes" customisation options, but you have the option to order the O2 with either black or silver endplates. I would recommend the black ones if you don't like to see scratches on your devices since the silver one that I have tends to easily show scratches (see photo below).
This is the only place where I have major complaints about the O2.
  1. Everything is on the front-panel, and the front-panel only
    1. 12 VAC AC adaptor plug
    2. Power button
    3. 3.5 mm output
    4. Red LED power indicator
    5. Volume potentiometer
    6. Gain button
    7. 3.5 mm output
Yeah...there's a lot stuff going-on on the front-panel, and the cable management is a mess.
Adding to the mess of stuff on the front-panel, the amp itself is too big (for me) to be considered a portable amplifier. Perhaps for those people who carry around a "portable" bomb rig that is 6-inches thick with 4 different components and paired with a 10 pound open-back Audeze LCD-2 headphone with $500 platinum-coated silver interconnect cables (slight exaggeration here), this amp is trivial in size; but I am not one of those people and I prefer to have a tidy, pocketable portable rig instead.
Kidding aside, the other thing that bothers me with the O2 is the channel imbalance encountered at low volume-levels with the potentiometer. When past the channel imbalance region (~8:30 o'clock position on the potentiometer), the output is kind of loud even with 1.0x gain, especially with sensitive headphones. Because of this, I don't really recommend the O2 for such headphones unless you have a custom gain of less than 1.0, or you use an impedance adaptor.
As a small note, at least with the V-MODA Crossfade M-100's cables, my O2 doesn't seem to like TRRS jacks too much. If I plug it in all the way, I get a mono-like sound coming out of the O2. Pulling out the jack slightly seems to remedy this issue and all is good.
All things considered, the layout of the O2's front-panel is messy and the potentiometer's channel imbalance can be a bit of annoyance for some headphones.
The O2 outside of its case:
From switching between different amps, headphones, and sources I have at hand, the O2 has a very clean-sounding signature as a whole.
  1. Bass extension is good with decent texture
  2. Midrange is a bit laid back in presentation, but not lacking in detail
  3. Treble is well-extended with no roll-off from what I can detect
  4. Soundstage is pretty spacious, having both good width and depth
  5. Related, but not necessarily correlated to the soundstage, imaging is also very good and I can easily imagine where instruments are in my head
  6. Instrument separation is excellent; instruments are well-defined and never muddled together
  7. Related, but not necessarily correlated to the instrument separation, instruments have very good detail and nothing sounds muffled
  8. There is no background hiss from what I can hear with 1.0x and 2.5x gain options at reasonable volume levels
Q: Is this what neutral sounds like?
A: I have no idea. I'm not a musician, nor do I play any instruments, so I can't say if it sounds coloured or not.
Q: Is this what a "wire with gain" sounds like?
A: Maybe. This relates to the previous question.
Q: Is this what "boring" or "sterile" sounds like, as some have suggested?
A: Not in my book. Different genres of music of all different kinds of mastering sound fine with me. I have yet to encounter a track and exclaim: "wow this amp is so boring! my music sounds so dull and lifeless!" All I can say is that music in general sounds spacious, well-defined, and clear. Though "involvement" in music is purely subjective, I never find myself being uninvolved in my music unless I'm listening to music as background noise.
Q: Will it power X headphone adequately?
A: Yeah most likely. I really enjoyed the LCD-2 with the O2 over other amps I've heard, even though the LCD-2 isn't my favourite headphone of choice. From a pure synergy perspective, I didn't like the HE-500 with the O2 as it had a pretty tizzy treble that made rock tracks not enjoyable for me to listen to. That might be due to the HE-500 itself though, not the O2.
Q: Does it sound bright?
A: Not at all. I don't know where people got that idea from.
 bright, brilliant The most often misused terms in audio, these describe the degree to which reproduced sound has a hard, crisp edge to it. Brightness relates to the energy content in the 4kHz-8kHz band. It is not related to output in the extreme-high-frequency range. All live sound has brightness; it is a problem only when it is excessive.

Comparing different headphones with the O2 and comparing the O2 to different amps, the O2 is definitely not bright to me. It's definitely not dark either for that matter. Maybe with an HD800 or K 701 they sound bright, but the those headphones are bright by nature, so it's not the O2 sounding bright.
All in all, if you can get past the messy front-panel and the channel imbalance at low volume-levels, then I truly think the Objective 2 is a terrific-sounding amp. I like its sound more than other amps I've tried, both desktop and portable amps, and everything just sounds so dang clear and clean to me. As such, the O2 is my current reference amplifier. For $140 USD, I think the O2 is a no-brainer if you're looking for a clean-sounding amplifier and you don't want to spend OVER 9000!!!!! (read: a lot of) dollars on an amp. You might not like the sound of some headphones out of it, but I think it's due to the headphones themselves and not necessarily the O2.
Thank You!
Thank you for taking the time to read or glance over my review! I hope this review helps you in some way or another and if you have any questions, feel free to leave a comment below.
Happy Listening!

Makiah S
Makiah S
 Liked your review, will totally steal some of that for my own Amp reviews :D [gathering a song list for amps, not gonna do song by song break down for an amp, but pictures and how it pairs with headphones personally]
So BRILLANT IDEA'S STOLEN <3 Thank you :D [and I did enjoy it ]
Thanks for the review. I've been loving mine since I got it. I'm convinced it's very transparent, but it does seem to have a hint of brightness in the treble with some headphones (not coming from the headphone). Less so than the Magni I previously had. Barely audible and only shows up with bad tracks. I still think it sounds transparent. The real test is spending years with it and seeing if it doesn't alter the stock signature of any of my headphones.
So far I haven't disliked a headphone with the O2 yet (due to the amp) but maybe sometime?
Good review. I've found mine very transparent and excellent, but the rechargeable cells used in mine (made by the now-defunct Epiphany Acoustics) are rubbish and degraded significantly after a few months. I could easily replace them (the housing just pulls apart) but for how often I actually want to transport this thing, there's just no point. This is probably an issue that varies from assembler to assembler, as I doubt the original specs detailed an exact brand/model of rechargeable cells to use.


Headphoneus Supremus
Pros: Transparent (duh), Not bright/thin/cold and requires no specific type of headphone
Cons: don't like the inputs on the front
Just a few impressions since nobody really reads these:
  1. All my headphones work well with it. Everything sounds just like it should. Garbage tracks actually still sound like garbage.
  2. Very revealing (yes, I know) and if my recording sounds tinny/harsh/thin it will sound like that (unless I'm using the HD-650) without any change
  3. Doesn't sound bright (if it does, it's the recording or headphone) and doesn't require a specific type of headphone for good "synergy" (IMO so far).
  4. Doesn't sound cold/thin etc. It's warm (sounding) if the recording or headphone is. Some recordings sound like they have all the warmth sucked out.
  5. Sounds crystal clear really. It actually might sound maybe a tad cleaner than my Micro Amp + Astrodyne. Barely audible, but I noticed it.
  6. Didn't notice any "larger soundstage" nonsense, but I did get an impression of a little more detail. I think i'm just fooled really.
  7. I would say it sounds perhaps 97% identical to my Headroom Micro Amp + Astrodyne. Impressive! The Micro might have a tad more body to the sound, but barely audible. It's not warm!
  8. I can't say this enough, but the O2 sounds closer to the Micro Amp than the Schiit Magni (IMO).
  9. I don't like the layout and would gladly pay $50 more for a design with inputs in the back. I'll live.
  10. If you like a just a slight touch of warmth on your amp I would suggest instead the Fiio E9 or get an E17 as a DAC.
  11. I don't really know what else to say. Nothing really WOWs me except for how crystal clear it sounds (with the right music) and how close it is to my favorite Micro Amp.
  12. Tested with Schiit Modi, E17 (DAC) and HD-650, K400, Q701 (+Annie pads), Koss Pro DJ 100, HD-598.
  1. The coolest thing to me with this is the massive variation in how each recording sounds sometimes. At times it feels as if it's like going from an HD-650 to an AD700. This is with the Q701!
  2. So far I like this more than the Fiio E9, Asgard1 and Magni, but it's comparable to the Micro Amp in sound. Is it better? Not sure.
  3. Doesn't get hot. I just checked. Had it on the past 4 hours.
  4. Might sound .000005% better with the ODAC compared to the Modi. Modi and ODAC sound nearly identical to ME.
Sounds transparent. No, really. I bet you didn't know that! I've heard it with my own ears and agree.
9-20-13 UPDATE:
Seems like with the Q701 it has a very very very slight hint of treble brightness. Barely audible, but it's still great with bright headphones and won't make them worse really. I've read that upgrading to a different power supply might make the treble smoother. Doubt it, but maybe!
Guns in Fallout 3 are noticeably more ear piercing than usual, but not too bad.
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Wow. I had no idea I was the only one who reads these reviews. I'm not sure if I feel superior or stupid.
What different DACs were you using? I know you tried a FiiO E17, which is the only DAC I own, but I'm unclear about other DACs you tried. I think you are saying the FiiO E17 as DAC adds warmth, but what other DAC did you use to make that comparison?
So far I've only tried the Modi and E17 with it. IMO the Modi is transparent and I could not tell much difference between it and the ODAC. ODAC did sound maybe a tad clearer but I figured that was maybe my imagination. O2+Modi is a perfect setup IMO. I definitely prefer this to the Magni + Modi. The E17 has a touch of warmth compared to the Modi. A little more body to the sound but a smaller soundstage.


New Head-Fier
Pros: Noticeable improvement in some cases, very little improvement in other cases
Cons: Everything is on front panel
So, this amp makes the signal just a bit cleaner. It was pretty noticeable on my Q701s, noticeable for general clarity, separation, esp cymbals got a bit clearer. For my HD 558 (w/ foam mod), slightly noticeable, but not that much. For my closed-back headphones->very minuscule, you might notice if you listen really hard. When I bought this, I just needed power for my Q701s so I was surprised the quality actually improved, thus I might have exaggerated my initial impressions a tiny bit. Overall the difference minor even for the Q701, but still pretty noticeable. It's not OH WOW I CAN'T BELIEVE THIS, IT'S LIKE DAY AND NIGHT kind of difference.
I bought this amp for my Q701s (Which I won't receive until Friday). When it came I took it out just to make sure it works (All my current headphones are low impedance and don't require an amp). I hooked it up with probably one of the worst possible sources you can imagine: a Nintendo DS (I was in the middle of playing a DS game when it arrived). Of course there was volume, but I also almost immediately noticed that the soundstage got bigger and the instrument separation became better. This was on my AD700s. I thought to myself it must be me imagining things. Just to make sure I switched back to directly plugging into the DS and the DS->Objective2->Ad700 setup. There really was an improvement, not just volume, I adjusted the knob so that the volumes were the same. The improvement is definitely real and doesn't require careful listening to notice, it was almost immediately noticeable. Needless to say, I am impressed as I have always been skeptical of headphone amps, but this one made me believe all the hype.
I have Grado SR80's myself, also V-Moda M80's. Easily drivable with low impedance. Would they offer more potential for improvement with such an amp?
I can't really say because I haven't tested the O2 with those headphones (though I do have an M80 myself so I might do that later).
It depends on a lot of factors, such your original source also and the output impedance of that. Generally the 1/8 rule applies in which the output impedance should be at most 1/8 of the headphone impedance, otherwise the frequency response can get screwed up a bit. In this case you would hear a very noticeable improvement with the O2, since the O2 has near zero output impedance. On power hungry headphones improvement would also be very noticeable, since if the headphones are under-powered, it wouldn't sound right as well. I've heard out of an ipod, Q701 is more of a sidestep compared to AD700, however it's generally accepted and common knowledge that the Q701 is a big upgrade compared to the AD700. On my AD700 (32ohms same as SR80), sound was definitely cleaner. I think since my Amperiors have a much smaller soundstage, the difference was not as noticeable. There's a lot of factors, but I think you will definitely hear an improvement. The M80 and SR80 both have a bigger soundstage than the Amperiors. I can't guarantee substantial improvement, but I think it's better to just buy the amp. You should at least hear a small improvement and in case you want to upgrade to better headphones later, this amp will make a huge difference compared to an unamped source. I'm trying to be as helpful as I can since many things said here are subjective and you don't really know until you judge with your own ears.
How is the O2 with the Q701? Does it have enough power to drive it well?


100+ Head-Fier
Pros: Everything?
Cons: Need bigger am for HE-6?
Linear, low output impedance and never noisy without a "signature". If you want to listen to your headphones and not your voiced headphone amps I highly recommend this.


500+ Head-Fier
Pros: Does its Job and Does it Well
Cons: Pricey? Even for what you get . . .
Lets see, a battery powered Amp that runs for hours on hours with a charge, or a desktop Amp that can throw almost a watt out and run forever?
I don't know - its sort of both. It is too big to be taken anywhere, but definitely small enough to travel if you want it to. I ordered mine with a black face plate which I think is a little cooler looking.
There appears to be some "mythology" surrounding this amp, some claim it "ruins" their sound quality while others think its awesome. I think its an amp - that is, it takes a signal, amplifies it, and otherwise has no real impact on what you hear. It has no real noise I can detect (except at max gain of 6.5X with nothing playing at max volume, which is possibly my source, not the amp). Those who adore vacuum tubes might hate this discrete amp, but I hate replacing tubes every 9,000 hours, and like the idea that this thing should run forever
As far as amps go, the sound quality has been awesome, convincingly "clean", and does not seem to distort or struggle even when being pushed hard. You would have to spend at least another $50-100 bucks or so to get to the next level of power (about 1 full watt) with similar features and quality.
Mine came with small stick-on rubber feet, and a blocky 12 V DAC adapter. Having all jacks in the front is not a HUGE deal, but function is definitely following form in this case. Clutter could be reduced if the power and input jacks were in the rear, but you'd have to do these mods yourself. On that front, it would be nice to have digital/RCA/USB inputs as this unit probably isn't going anywhere. Whole unit has a nice solid feel, volume knob is solid feeling. Only gain and power switch come across as a little "cheap". I ordered stock 2.5X gain and 6.5X gain switch - which is about right for my HE-400s. For a more efficient headphone, as you can choose gain level, I would recommend 1X gain and perhaps 2.5-4X for less efficient cans. If you listen to many High Dynamic Range recordings (like DVD movies, for example), you may want that high gain (6.5x) switch - it can help reach the right volume levels with certain headphones. But, in general, the gain settings are not 'volume' buttons consider your main sources.
JDS Labs shipped extremely fast, answered my questions, and will "customize" the unit by shipping it with gain settings and color of your choosing. You can choose your own VAC adapter, or just buy theirs, as I did.
Prodigous power from a small unit - I estimate about 700 mWs @ 50 ohms while plugged in. Otherwise, about 500 mWs reliably from about 32-100 Ohms plugged in, and about 500-400 mWs on battery. Far more power than needed for most headphones. Very low impedance output should be a great match for a very wide range of headphones. This thing specs better than amps several times its price.
That said, it also costs almost as much as very good component amps for cars (that provide 10x the power). It costs as much as some very good headphones. In the world of high-end headphones, it is a fabulous value. But I would probably skip it if you get enough volume from current sources. The HE-400 provides a fairly good threshold perhaps (rated 92dB efficiency). Any phone with efficiency ratings in the 95 dB or greater range probably doesn't want this much power. But if your phones are high impedance and you struggle getting good output from a computer, phone, etc, I am sure the O2 will rock your world.
Thanks for the informative review, I shall place an order for this little beast soon. I love great powerful little amps and already have a fiio e12.

Magick Man

Daddy Warbucks
Pros: Good sound, low price, portable
Cons: I don't like the layout
Okay... I believe the O2+ODAC combo is a good product for the price.

Yeah, that does sound like a cop out, doesn't it? Alright, I'll try again.

With headphones that this unit will normally be paired with; HD650, Q701, HE300, FA-003, etc. (solid mid-fi cans), I think it does quite well. To me it stumbles where most SS mid-fi amps stumble, it's a little on the bright side of neutral and highs are a bit etched. Also, mids do seem slightly congested and bass could be tighter. Also, mine has a slightly scratchy volume pot (not a huge deal, probably just needs a shot of DeoxIT). I don't think it drives my T1s very well, same goes for the TH900. Those foibles I mentioned before seem to get magnified. The HE-6? Fugetaboutit.

"Oh, he hates it", no I don't. It isn't some Class A monster, and my Onkyo P-3000R ($1700 MSRP) does knock its lights out, but it's $300 and has batteries for cripes' sake. Personally, I feel the DAC is quite good, though I wish it had some type of S/PDIF connection, and as a package it punches above its weight class. IMO, it isn't David knocking out Goliath, it's a Golf GTI out handling the mid-range pony cars. Overall a good value.
Put ANOTHER ferrite ring on the USB cable. I though it was my ears or my phones but an extra ring killed the top end crap. I agree it did not sound too bad with HD600s but was too much with my Sonys. I could not play half of the best of Jethro Tull!