# Small Objective 2 Review



## SpaceTimeMorph

*To Start…*
   
  There are a lot of amps out there that use exotic topologies and expensive parts.  Even “budget” amplifiers try to get in on this game.  Too often, that practice fails and you end up with a “transparent” amp that is anything but.  Or an amp is made that trades reliability for a perceived gain in sound quality.  Is there anything out there that can faithfully reproduce an audio signal without jeopardizing your headphones?  This is a review of a DIY-product, the Objective2 amplifier (O2 for short), that attempts (and succeeds IMO) to realize those goals.
   
  So, if you are looking for an amp that can be perfectly transparent, can power a number of hard-to-drive headphones, and that costs less than $200, read on.  If you are looking for the next big tube amp, or an amp to help offset whatever coloration you are looking to offset, then the O2 amp probably isn’t for you.
   
*Details, sir:*
   
*[NOTE: *The O2 was designed to be a portable and a desktop headphone amplifier.  As such there is a difference in the maximum gain that can be realized on AC power versus on Battery power.  This is due to the differing rail voltages connected and disconnected from the grid.  The numbers for maximum gain are: 7/Vin for AC power, and 4.5/Vin for Battery power (both RMS voltages).  This will cover all charge states from the batteries.*]*
   
  This amp was a loaner from NwAvGuy (aka Lord Voldemoort).  It is completely “to spec” according to his design, using the suggested enclosure, board configuration (all board mounted jacks and buttons, for example), wall wart, and front panel.  The DIY version can be had for ~$100 (for the entire amp) or for $150 via Mr. Slim on diyaudio.  The gains are set to 2.5x/6x. 
   
  Headphones used:  Ultrasone Pro 900, Shure E3C, Shure SE 535-V, ATH M50, Beyer DT-880 Pro 600ohm, and Senn PMX-680i (yes, I tried working out with this thing; more on that later).  Sources: diy-MOD 5.5g, Sansa Clip+ (both rockboxed), Cambridge Audio DAC Magic, Emotiva XDA-1, and an Astro Mix-amp.
   
  Music: Danzig, Static-X, Norah Jones, Pendulum, TCM, CCR, Miles Davis, John Coltrane, Charlie Parker, Pheonix, Aesop Rock, Atmosphere, Clutch, Xx, Tristeza, Mars Volta, Maurizio Pollini etc.  In short, just about everything, all FLAC/CBR  MP3 @320kbps.
   
*Aesthetics & Build Quality:*
   
  The B2-080 enclosure is a plain, though good looking enclosure.  Box Enclosures gives you several different choices for colors (mine is bronze).  The case itself is solid, and if you wanted, you could use it to punch holes in walls.  Sorry, no demonstration of that will be forthcoming.
   
  Even though the case itself is solid, the controls on the front side stick out enough that if you were to drop it on one of those, expect something to break.
   
*Some minor Quibbles (non-sound related):*
   
  Got to mention the size here.  It is probably too big to fit comfortably in most people’s pockets for active use.  It fit in my cargo shorts just fine, so walking around with it at the airport, etc. probably wouldn’t be too big of an issue for me.  But most people probably would want to throw it in a backpag/bag or just use a smaller amp for this purpose.  When I tried working out with it, I had a hard time keeping it in my pocket for a good portion of the workout.  So, to echo what others have said, this amp is more of a transportable amp than a true portable amp.

  Another minor thing is the fact that all of the controls/jacks are on one side of the amp.  This caused problems for my fat fingers when I tried operating some of the controls.  Since this is a DIY design, there is the possibility of mounting the board backwards within the case and remote mounting some of the jacks on opposite sides of the board as you see fit.  I would recommend that for those people with coordination issues (such as me).

  Battery replacement could be a little problematic.  You have to unscrew and remove the back panel first.  Then the batteries are mounted flush with the board.  Removing and then reinserting them could be a hassle without stressing the board-mounted terminals overmuch.  The other option is to remove the board entirely and then replace the batteries.  Either one is a bit cumbersome.  However, if you use the recommended NiMH 9-V batteries, this shouldn’t be an issue for a good long while.
   
*Sound Quality:*
   
  What is there to say about an amp that literally adds nothing of its own to the sound signature?  Any variations I heard in sonic characteristics were most certainly due to my headphones and not the amp. 
   
  The O2 produces sound that is faithful to the original recording, without producing colorations or edge on the music.  You can hear punchy, forceful bass, detailed midrange, or whatever else is in the playback chain.  I compared this amp to the ALO Rx Mk II and the Headamp Pico (amp only).  I was unable to discern any major differences between the amps, although I thought that the O2 had a slightly more laid back sound than the ALO amp (wouldn’t swear to this on a DBT though).
   
  Much fuss was made on the gain structure of the amp.  Placing the volume pot after the gain stage was said to make the amp prone to input overloading.  With careful selection of your gain setting with respect to your source and your headphones, this is not a problem.  (Much more on this has been said on NwAvGuy’s site if you are looking for more information).  With ReplayGain set to 85dB, the O2 was able to drive even the Beyers to acceptable levels without clipping noticeably, even on battery power.  This is something that neither of my other portable amps can even come close to doing.
   
*Summary:*
   
  In conclusion, overall what do I have to say about this amp?  Everything I listened to was crystal clear.  No undue colorations or “grain/edge/harshness” to note.  Also, it was subjectively very close to a couple of amps many times its price.  In short, the Objective2 is what it intends to be, a transparent, noise free amplifier that brings back the fidelity in hi-fidelity and sets the bar ridiculously high in terms of price/performance ratio.
   
  For further reading, check out NwAvGuy’s website, especially his O2 Summary article.


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## Willakan

Great review. Not much more to add, all the O2 reviews are looking pretty similar (sound is unsurprisingly of the "wire with gain" kind, bit big for a portable amp, wish it had front and back panels)


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## upstateguy

subscribe


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## maverickronin

Cool.  Someone else likes it.  I must not be crazy after all.


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## mikeaj

I'm gonna call BIAS on this review for getting a review sample. Also, such a cold and clinically sterile amp is only good for "pleasing the meters" and not offering "better sound for human's ears." Since this is O2 review, you are only supposed to listen with oscilloscope.

1/5 review. :rolleyes:


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## Head Injury

Quote: 





mikeaj said:


> I'm gonna call BIAS on this review for getting a review sample. Also, such a cold and clinically sterile amp is only good for "pleasing the meters" and not offering "better sound for human's ears." Since this is O2 review, you are only supposed to listen with oscilloscope.
> 
> 1/5 review.


 

 You mean this amp has a flat frequency response? But how will I ever listen to bright headphones again?
   
  1/5 for your review of the review


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## SpaceTimeMorph

Quote:


willakan said:


> Great review. Not much more to add, all the O2 reviews are looking pretty similar (sound is unsurprisingly of the "wire with gain" kind, bit big for a portable amp, wish it had front and back panels)


 
  You know, it also cures cancer .  Just thought I'd be the one to tell you.
    
  Quote:


maverickronin said:


> Cool.  Someone else likes it.  I must not be crazy after all.


 
  Definitely not.  I just think that if I wanted to I could distort my sound through EQ to all get out if I wanted.  Neutral sound suits me better.  But, we _must _be biased, unlike all of those other reviewers that get free samples... jk.
  
  Quote: 





mikeaj said:


> I'm gonna call BIAS on this review for getting a review sample. Also, such a cold and clinically sterile amp is only good for "pleasing the meters" and not offering "better sound for human's ears." Since this is O2 review, you are only supposed to listen with oscilloscope.
> 
> 1/5 review.


 
  Just....lol.
  
  All who care, got my front panel in from Front Panel Express.  I have some minor misfit issues, but I think it is due to a slight warping of my sample's pcb (it's pushing the headphone jack upwards slightly).  So I will be working on posting pictures here shortly.


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## maverickronin

Quote: 





spacetimemorph said:


> Definitely not.  I just think that if I wanted to I could distort my sound through EQ to all get out if I wanted.  Neutral sound suits me better.  But, we _must _be biased, unlike all of those other reviewers that get free samples... jk.


 

 I use EQ all the time, I just prefer neutral amps and DACs for practical reasons.  By taking as many variables out of the signal path as possible I can more easily find the sound I want via a combination of the right headphones (since there aren't really any "neutral" headphones they have to be considered too) and the right DSPs.  A DSP can add anything your transducers can reproduce but it won't be able to take away much of anything beyond simple frequency response or level issues.


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## khaos974

The current batch of O2 reviews are pretty useless considering that only 'objectivist' (using the term loosely) have built them yet, and since these review embrace the philosophy that all amps sound the same as long as the measurements are ok, these reviews have no purpose

Another 'objectivist' would be already convinced of the 'wire with gain' sound of this amp simply by looking at the published measurements, and a 'subjectivist' will think that this would be a review by a tin-eared person since the reviewer doesn't hear the 'obvious' differences between DACs and amps so they wouldn't be convinced. It's basically preaching to the choir.

BTW, is it really useful to have a separate thread for each O2 review? 

By the way, it looks much better than I expected.


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## Satellite_6

Quote: 





khaos974 said:


> The current batch of O2 reviews are pretty useless considering that only 'objectivist' (using the term loosely) have built them yet, and since these review embrace the philosophy that all amps sound the same as long as the measurements are ok, these reviews have no purpose


 
   

 I concur. We need a review where someone can actually hear differences between other amps. Sorry but I don't agree that all amps sound the same. . . although I am really starting to think of myself as an objectivist, I cannot accept this view.


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## khaos974

satellite_6 said:


> I concur. We need a review where someone can actually hear differences between other amps. Sorry but I don't agree that all amps sound the same. . . although I am really starting to think of myself as an objectivist, I cannot accept this view.


 

I wrote all amps with ok measurements, most 'objectivists' would agree that any amp with less than 0.01 % THD+N across the spectrum, low IMD , more than 100 dB SNR, a flat FR, a less than 1 ohm Zout, no phase or stability issues would sound indistinguishable from each other as long as they are not pushed past their clipping point.


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## qusp

Quote: 





satellite_6 said:


> I concur. We need a review where someone can actually hear differences between other amps. Sorry but I don't agree that all amps sound the same. . . *although I am really starting to think of myself as an objectivist, I cannot accept this view. *


 
  thats good, because you can only think of yourself as being an objectivist, you, as a human being, cannot actually be one. listening to something objectively is a tautology


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## Satellite_6

sure, yes, indeed.


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## dachness

Enclosure specs if any one is wondering: http://www.boxenclosures.com/category/product_details.html?product__id=211292


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## Inks

Wish the amp were smaller.


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## maverickronin

Quote: 





inks said:


> Wish the amp were smaller.


 

 That's about its biggest weakness.  It can't really be made much smaller without sacrificing most of its performance or changing everything to surface mount and being a lot harder to build.
   
  Maybe if we're lucky it will get popular enough for a company to copy the basic design but make it smaller by using surface mount components and probably a lithium battery with DC-DC bipolar converter for the power supply, presumably verifying the performance with Lord Voldermort to comply with license.
   
  That's probably just wishful thinking though...


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## estreeter

Beats me - while the CLAS stack is held at the pinnacle of transportable audio, I dont see this as 'too big'. I'd prefer a small pricetag and a large enclosure than the other way around - just my 2 cents worth.


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## Maverickmonk

Everytime I see this I want one. Someone needs to start carrying these boards in stock


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## Head Injury

Quote: 





estreeter said:


> Beats me - while the CLAS stack is held at the pinnacle of transportable audio, I dont see this as 'too big'. I'd prefer a small pricetag and a large enclosure than the other way around - just my 2 cents worth.


 

 So would I, but I don't bother with a portable amp so I'm not part of the same market.


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## vizzle

Did someone try o2 with k701/2? any opinion?


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## mikeaj

Quote: 





vizzle said:


> Did someone try o2 with k701/2? any opinion?


 

 One opinion, of a slightly earlier revision of the amp I think (with larger turn on/off transients maybe; nothing in actual sound should have changed since then):
http://www.head-fi.org/t/568705/review-nwavguys-o2-diy-amplifier


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## Willakan

Quote:


vizzle said:


> Did someone try o2 with k701/2? any opinion?


   
  It has easily enough power for them, so should sound great. I will be using them with my amp build, which has just flown through testing with flying colours. Watch this space!


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## upstateguy

Quote: 





head injury said:


> So would I, but I don't bother with a portable amp so I'm not part of the same market.


 


  Hi HI
   
  I don't think there will be an audible difference between the portable version and the desktop version.
   
  I really don't need a portable since I'll be running it off AC, but, hey, if it runs on batteries too, what the heck....


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## Maxvla

I mostly want the desktop version for it to be a more proper size/layout for desktop use. Portables tend to have all the controls and plugs jammed together.


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## estreeter

Got the answers I was after from Oliver at Epiphany Acoustics - eagerly looking forward to my amp. Found some photos with the 'recommended enclosure' on a Hong Kong forum, but I expect that they have already been posted. FWIR, it seems that the stock opamps are the way to go, at least if you want the same results nwavguy published.


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## vizzle

Quote: 





estreeter said:


> Got the answers I was after from Oliver at Epiphany Acoustics - eagerly looking forward to my amp.


 

 My Epiphany Acoustics o2 arrive just 3 days ago, now need Fiio L7 to connect it to DAC (e7).


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## vizzle

Some pictures:
   
   
  1. o2 Front

   
   
  2. With AKG k702

   

   

   
  3. Size comparison (from left, Samsung Galaxy SII, o2 itself, mouse, Fiio e7, Sansa Clip+, Fiio e9)


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## estreeter

Very nice, vizzle - next to large cans like the AKGs, it doesnt look as 'huge' as some had earlier complained the Objective2 was for a 'portable' amp.


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## scuttle

Quote: 





satellite_6 said:


> I concur. We need a review where someone can actually hear differences between other amps. Sorry but I don't agree that all amps sound the same. . . although I am really starting to think of myself as an objectivist, I cannot accept this view.


 

 The Objectivist argument isn't that all amps sound the same. It's that all GOOD amps sound the same - because they're supposed to reproduce the original sound and the more exactly they do that, the better they are. To me this is inarguable.


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## upstateguy

Quote: 





scuttle said:


> The Objectivist argument isn't that all amps sound the same. It's that *all GOOD amps sound the same* - because they're supposed to reproduce the original sound and the more exactly they do that, the better they are. To me this is inarguable.


 


  In theory that is true, but in reality, over time, one develops preferences for one amp over another.


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## avaddikt

There are many things about which I am not so pragmatic, but this one will not make it for my purposes. Some are content with a 'small amp' but others_ truly _want a 'pocket amp'.  There could be some issues in kit building a smaller package also, although the 'tin amp' folks say, "not really". Unless there is a significant difference in AQ with a PA2V2, for example, I have to pass. I can certainly appreciate the design and effort though, and thanks to the OP for exploring it for us.


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## proton007

I think the PCB itself is kinda small, but the caps and voltage regulators need some space. Maybe its because it can work with off the wall AC with adaptor, I'm not sure. 
  I wonder what the other portable amps use to keep the volume small.


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## maverickronin

Quote: 





proton007 said:


> I wonder what the other portable amps use to keep the volume small.


 
   
  Surface mount components.  It would have been trivial to design the O2 to use them but then pretty much nobody would be able to DIY it since the parts would be too small for most people's soldering skills.  Surface mount stuff is normally all done by machines.
   
  The only other popular and portable DIY amps are the Mini3 and the cmoy which are less complicated designs.
   
  Lithium batteries also help but they're very fussy about proper charging and releasing such a design to novices is just going to invite house fires and amps blowing up in people's pockets.


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## crazywipe

A lot of peoples really hates the O2 because for 150$ you get 90% performance of any thousand dollar offering. I really think many peoples can stuck with the o2 for all their life with no reason to upgrade. 
  I went to a very friend of mine house to try the o2 and a 2000 EUR otl tube amplifier. He told me: "DON'T WASTE YOUT MONEY AND GET THE O2, IT HAS A BIGGER SOUND LIKE MY OTL"
   
  That's all guys
   
  Hope you are happy with your huber turbo 12 valve 5000$ amp advertised on headfi. I'll happily stuck with my new O2


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## estreeter

Quote: 





crazywipe said:


> A lot of peoples really hates the O2 because for 150$ you get 90% performance of any thousand dollar offering. I really think many peoples can stuck with the o2 for all their life with no reason to upgrade.
> I went to a very friend of mine house to try the o2 and a 2000 EUR otl tube amplifier. He told me: "DON'T WASTE YOUT MONEY AND GET THE O2, IT HAS A BIGGER SOUND LIKE MY OTL"
> 
> That's all guys
> ...


 
   
  Then his '2000 Euro' tube amp is a poorly designed piece of crap, or the rest of his rig isnt up to scratch. Seriously, even V himself would have trouble accepting that sort of *crazed fanboyism* - can we just get a grip, please ? I've been using the O2 since January - its very transparent, but I dont think Woo Audio are going to stop making amps on the back of this little DiY marvel. You could count the number of head-fiers with *5K amps* on one hand, btw.


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## alphaphoenix

For those who've owned the O2 and various other amps, I think the consensus is around that the O2 is a very, very good for what it is and it's price range.  Anyways, most DIY amps fall under this category of "best performance bang for the buck". 
   
  However, to state that one could be forever happy with the O2 versus a 5K amp or even a $500 amp with no reason to upgrade seems a little far fetched.  This is why I stress getting more experience to different equipment and truly make the self determination once you've A/B/C/x all the other offerings in the crazy hobby.  Like most things, any objective spec usually excels with a particular setup and just OK with others.
   
  Yes. the O2 created big stir and obvious fans by it's relative low entry price and the creator's agenda.  But it's really no different than any other DIY project of the past with performance levels far exceeding it's build price.  When I built the Mini3 and MSSH, I felt the say way - "best performance bang for the buck".


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## sashaw

There is really nothing to complain about it, except the case. Just like LISA III, the size is kind a bit to big for portable. and the connectors are located on the long side, so the cable will be hanging out and loop around the corner. Not really portable, LOL.


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## adydula

yes people will buy the more expensive stuff because there is and will always be the "gee this low cost therefore low end' stuff cant be as good as the mega buck stuff...
   
  if these folks would be able to do the blind listening test...they might change there mind...well maybe not...
   
  Smilng....
   
  Alex


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## audionewbi

Is it me or does the O2 suffer from lack of mids. I give it more time, it just arrived. I might try some AD826 opamp on this. For now the gain is enough for the ER4S but it lacks mids and low end compared to what I hear from my dac on board head amp( it is a bresford caiman with the gator board FYI).
  
  But never the less it is a keeper good price, great size.


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## adydula

I dont think it lacks anything especially mids....the thing with electronics that are indeed flat and transparent is the actual source, ie the cd or flac etc...is now mercilessly exposed...make sure you try a wide range of music....I look for recording and re-mastering of music that I know is the best. I have recordings on the same music some great and some lousy..same song etc...I have a thread on another site that all we do is look for recordings that are NOT compressed and have the fullest range and most dynamics...etc.
   
  thats whats so nice about the 02 amp and ODAC....its back to finding great music, well recorded AND mastered.
   
  Alex


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## audionewbi

Either the unit required burnin or my brain got used to the tonne. It sounds just fine now. But the treble at the begining gave me a terrible headache. I allowed the unit to play for 30 hours and came back and things sounded much better.


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## goodvibes

Quote: 





scuttle said:


> The Objectivist argument isn't that all amps sound the same. It's that all GOOD amps sound the same - because they're supposed to reproduce the original sound and the more exactly they do that, the better they are. To me this is inarguable.


 
  How good? It's all so relative to associated kit and usage.


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## goodvibes

Quote: 





spacetimemorph said:


> Much fuss was made on the gain structure of the amp.  Placing the volume pot after the gain stage was said to make the amp prone to input overloading.  With careful selection of your gain setting with respect to your source and your headphones, this is not a problem.


 
  To be clear, the volume control is between 2 Gain stages which is always the best way to use them. I don't know the input spec but if it can handle 3V in, I don't see a problem.


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## stv014

Quote: 





audionewbi said:


> Is it me or does the O2 suffer from lack of mids. I give it more time, it just arrived. I might try some AD826 opamp on this. For now the gain is enough for the ER4S but it lacks mids and low end compared to what I hear from my dac on board head amp( it is a bresford caiman with the gator board FYI).


 
   
  Maybe the onboard amplifier has a high output impedance, and that changed the sound of your IEMs (boosting the mids) compared to the O2 ?
   
  Replacing the gain stage op amp with the AD826 is not really recommended, and is unlikely to actually improve the sound anyway (it is definitely more noisy than the stock one, for example).


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## ulogin

And you could include an internal switch, making the O2 capable of doing 1x, 2.5x and 6x gain at the same time:
How to: O2 with Triple Gain Switch


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## stv014

Quote:  





> Mind you, everything I've read is that it a giant killer and I wouldn't pretend to know as much as Voldemort but if some think it's a bit laid back or lacks a bit of energy, you could always try giving the output stage some gain. Unity gain can sometimes have more feedback than optimum sonically but I'm in no way saying that's happening here. Just something to try for those that may feel that way.


 
   
  It is actually intentionally designed to have as much feedback as possible, to minimize distortion in the output stage. Further improvement is achieved by running two NJM4556 buffers in parallel, also doubling the maximum current output. Regarding too much feedback, I (and probably the designer of the O2 as well) recommend reading this article by Bruno Putzeys.


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## goodvibes

I get the circuit and qualified my response. There are definitely cases where more feedback is not preferred and I never said this was one of them. I've heard it compared. There's also a difference between 'too much feedback' which I never said this had and subtle character change. While I'm a big fan of the designer and prefer his methology to a lot of the snake oil out there, I also know that there are subtle differences to be had by massaging a circuit. In fact he did the same before finishing this amp. Distortion levels were already below what would be considered audible when he still heard changes in part selections. If they also measured better, was it the measured distortion that was audible at a 1/1000 % or some other non measured effect on the circuit? Being concise with design is a big deal but the best designers I've seen are aware that they don't know everything nor pretend to. I'm also not a zero feedback guy and use Naim at home. (Plenty of feedback)
   
   Without even hearing it, I think this amp is a great achievement and Voldemort deserves all the Kudos he gets. In fact I played around with one of those 4556 ebay amps he blogged about, got the offset to 1mv with gain at 3db, balanced the lamp diode across both rails for a balanced drain etc and it clearly sounds better than an e11 for instance. Part of the finalization were a few bypass parts which I'm generally not a fan of (prefer the right better ones) but this was cheap and cheerful with bits about. These parts wont change the measurements in any important way but are audible. I am neither a measurement (very important) nor a subjective zealot. Seems most folks pick a camp and hunker down.
   
  I'm out because I'm beginning to have words put in my mouth.


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## antberg

Guys just a question:I am looking to buy a O2 units for myself as i am (as always) tight on budget and it seems that this great amp could be a good start ,even if a basic one,to drive a pair of HD650 that i will try to buying soon.So i have been looking in my town for an adapter and the only one i found was 14Vac with 500 Mah.
   
  Does someone with a similar power adapter have experienced some overheating of the unit,taken the amperage?or it is best to find one with 200/300 Mah?
  Thanks for the input guys.
  PS:To be honest i am in doubt if i have to get more patience in waiting the awaited ODA....


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## audionewbi

Quote: 





antberg said:


> Guys just a question:I am looking to buy a O2 units for myself as i am (as always) tight on budget and it seems that this great amp could be a good start ,even if a basic one,to drive a pair of HD650 that i will try to buying soon.So i have been looking in my town for an adapter and the only one i found was 14Vac with 500 Mah.
> 
> Does someone with a similar power adapter have experienced some overheating of the unit,taken the amperage?or it is best to find one with 200/300 Mah?
> Thanks for the input guys.
> PS:To be honest i am in doubt if i have to get more patience in waiting the awaited ODA....


 
  He unit does get warm but what exactly do you mean by overheat? Mine gets relatively warm after 2 hours of usage but I can still hold it in my hand with no problem. 

 How warm does it get, can you hold it in your hand without burning your hand? After how long of connectivity do you experience this?


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## antberg

hey ,Audionewbie,thank you for the quick response.
  No,i dont have yet the O2,i needed to find it's weird adapter before being able to put an order on it.i hope when the ODA is out to be able to choose which one i will get,if the unreleased version wont be much more expensive.
  By the way if get a little warm after 2 hour ,should be fine,i am just asking because of the various amount of different amperages (from 200 to 800 , if i remember correctly) availability and i remember somewhere some fellow recommending the lowest amperage possible to avoid the amp to get warm.Nonetheless i think 500 Mah for the only adapter i found should work properly.
  Antonio


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## audionewbi

Quote: 





antberg said:


> hey ,Audionewbie,thank you for the quick response.
> No,i dont have yet the O2,i needed to find it's weird adapter before being able to put an order on it.i hope when the ODA is out to be able to choose which one i will get,if the unreleased version wont be much more expensive.
> By the way if get a little warm after 2 hour ,should be fine,i am just asking because of the various amount of different amperages (from 200 to 800 , if i remember correctly) availability and i remember somewhere some fellow recommending the lowest amperage possible to avoid the amp to get warm.Nonetheless i think 500 Mah for the only adapter i found should work properly.
> Antonio


 
  ODAC is out. You can order it either as standalone or built inside the O2. As far as the PSU goes if you check the designers blog he has provided a detailed information of the recommened PSU for his amp. I cannot share you the link due to head-fi ban on his blog but if you google it I am sure you will find it.
   
  But again O2 is not the best sounding AMP out there, it is the best measuring amp in its price range and honestly a great buy if you can build it yourself. But when you buy it pre-built and than add the P&H there can be better 'sounding' amps out there than the O2.

 But what made me keep the O2 is simply great engineering, and complete lack of HISS when turning the volume knob.


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## agdr

Quote: 





antberg said:


> So i have been looking in my town for an adapter and the only one i found was 14Vac with 500 Mah.
> 
> Does someone with a similar power adapter have experienced some overheating of the unit,taken the amperage?or it is best to find one with 200/300 Mah?
> ....


 
  The voltage of the power adapter is what is related to how hot the two voltage regulators in the O2 get, not the current. 14VAC is perfect, as is 500mA.  The designer's listed power adapter recommend on his latest BOM (Dec 2, 2011) is 14 - 20VAC.  Originally he had specified 12VAC which proved a little too thin in cases with the amp heavily loaded and the power mains voltage from the wall socket being on the low side.  The upper 18VAC - 20VAC adapter voltage range is where the voltage regulators start getting a bit toasty.
   
  As for current, anything from 200mA on up is fine for most headphones, or 400mA on up for low impedance + low sensitivity cans (the case that draws the most current).  The O2 can push up to 140mA per channel, plus some chip and part quiescient current overhead to make it about 200mA per channel max, for a maximum current requirement of about 400mA total for both channels.  There is an additonal techy issue of the adaptor's transformer core going into saturation on each power line cycle due to the current spikes caused by the double half wave rectifier setup the designer used in the O2 power supply.  Probably doesn't make any audible difference, but to avoid that add about 20% to the adapter's current rating.  That takes the it up from 400mA to around 500mA for O2 absolute max load current requirements, so what you've found there is just fine.
   
  I use 16VAC + 400mA on two of my O2s and 16VAC + 1A (1000mA) on the other.  Works great.  I would have chosen 14VAC though if I could have found that combination in the US at Mouser at the time, to reduce the voltage regulator's heat dissipation a bit more.


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## antberg

audionewbi said:


> ODAC is out. You can order it either as standalone or built inside the O2. As far as the PSU goes if you check the designers blog he has provided a detailed information of the recommened PSU for his amp. I cannot share you the link due to head-fi ban on his blog but if you google it I am sure you will find it.
> 
> But again O2 is not the best sounding AMP out there, it is the best measuring amp in its price range and honestly a great buy if you can build it yourself. But when you buy it pre-built and than add the P&H there can be better 'sounding' amps out there than the O2.
> 
> But what made me keep the O2 is simply great engineering, and complete lack of HISS when turning the volume knob.


 
   
   Sorry Audio,i meant the ODA (Objective Desktop Amp),a "Desktop" O2 version with no batteries and some more input -and/or output - options ,based on what John Seaber from JDS Labs. told me.
  Unfortunately "who should not be named" is not giving much more info about when it will be released,but there should not be any big great sound improvement from the O2.Nonetheless i will wait some review when it will be on the market to have a chance to choose from those two.I wish i could build it by myself but i am very bad at soldering i will just throw out that money...but i don't deny i would like to try to build a second unit to get more knowledge about what each components do and how a simple amplifier basically make.
  By the way along Head-Fi, his site is providing a lot of information and knowledge which is the reason i respect it very much.Unfortunately i am having some more important priorities and my geographical and economic position don't allow me to afford an hi-end amp and dac.
  I was considering some amp-dac's like the Mini ,the Quattro and few more,but for 150 dollars ,at the moment ,is tempting me a lot because for that price many tell is a great sounding amp.
   
   
   
  Quote:


agdr said:


> The voltage of the power adapter is what is related to how hot the two voltage regulators in the O2 get, not the current. 14VAC is perfect, as is 500mA.  The designer's listed power adapter recommend on his latest BOM (Dec 2, 2011) is 14 - 20VAC.  Originally he had specified 12VAC which proved a little too thin in cases with the amp heavily loaded and the power mains voltage from the wall socket being on the low side.  The upper 18VAC - 20VAC adapter voltage range is where the voltage regulators start getting a bit toasty.
> 
> As for current, anything from 200mA on up is fine for most headphones, or 400mA on up for low impedance + low sensitivity cans (the case that draws the most current).  The O2 can push up to 140mA per channel, plus some chip and part quiescient current overhead to make it about 200mA per channel max, for a maximum current requirement of about 400mA total for both channels.  There is an additonal techy issue of the adaptor's transformer core going into saturation on each power line cycle due to the current spikes caused by the double half wave rectifier setup the designer used in the O2 power supply.  Probably doesn't make any audible difference, but to avoid that add about 20% to the adapter's current rating.  That takes the it up from 400mA to around 500mA for O2 absolute max load current requirements, so what you've found there is just fine.
> 
> I use 16VAC + 400mA on two of my O2s and 16VAC + 1A (1000mA) on the other.  Works great.  I would have chosen 14VAC though if I could have found that combination in the US at Mouser at the time, to reduce the voltage regulator's heat dissipation a bit more.


 
   
  Wow bro,you are really into it,congrats for your in sightings.Yesterday i did research all the principal "electric components shops" avenue in my town,and i did only found the adapter mentioned above..I don't know why ,but it is a strange power requirement indeed.Obviously i don't know much more cause i am more into Knives and Pans...I was almost convinced i would have to contact a personal made adapter,ahaha.Glad to know it is the proper PSU.Do you have three units...
   
  What do you guys expect for the desktop version?If there will not be great difference in sound i maybe will try to buy the Trans-portable version due to his batteries capabilities feature.And hopefully if it wont cost too much..


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## audionewbi

O my bad, yea that who cannot be name has not made a work about the ODA, I totally have forgotten about it. I am sure this time with the ODA he will be thinking of making a profit out of it.


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## adydula

The thing that makes this inexpensive amp great is that is doesnt have any sound of its own...its totally transparent....you can hear the source good or bad and hear what your cans are in a neutral environmnet.
   
  All the measurments that impacts the sound are beyond human hearing....
   
  And add to that its totally silent, quiet etc...
   
  Alex


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## quickboy2014

Nice review, thanks for the sharing


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## PurpleAngel

Anybody ever figure out what would be the effect if the O2 was redesigned with three 9 Volt batteries?
  You could automatically say the charge would last 50% longer.
  But as the workload on each battery would be less, does that make the battery more efficient for a given charge?


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## mikeaj

Quote: 





purpleangel said:


> Anybody ever figure out what would be the effect if the O2 was redesigned with three 9 Volt batteries?
> You could automatically say the charge would last 50% longer.
> But as the workload on each battery would be less, does that make the battery more efficient for a given charge?


 
   
  First of all, I don't understand what you mean by "efficient" in terms of the battery.  Could you maybe reword that?
   
  Secondly, having three batteries (in configurations that make sense) would alter the configuration of the amp.  As it is, one battery's - terminal is connected to ground, and the other battery's + terminal is connected to ground, so the first is generating the positive rail while the second is responsible for the negative rail.  How would you set up three batteries relative to ground?  If three 9V batteries give 27V, how do you make that +13.5V and -13.5V?  You'd need a rail splitter or some other solution.
   
  Also, note that if the supply voltages are higher, then the amp will draw more power.  In some portable amps (e.g. FiiO E11), a low-power mode actually just reduces the rails—that's how low-power operation is achieved.


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## audionewbi

does anyone know if MUSES01 works with this?


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## asak

> does anyone know if MUSES01 works with this?


 
   
  I have one but not a pair of them. Muses01 has 25mA max current output vs 70 mA for the recommended opamp. 
   
  For what its worth, tried a pair of lme49720. Sounded brighter than the stock opamps but the bass punch was weak.


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## audionewbi

Quote: 





asak said:


> I have one but not a pair of them. Muses01 has 25mA max current output vs 70 mA for the recommended opamp.
> 
> For what its worth, tried a pair of lme49720. Sounded brighter than the stock opamps but the bass punch was weak.


 
  thanks


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## stv014

Quote: 





asak said:


> I have one but not a pair of them. Muses01 has 25mA max current output vs 70 mA for the recommended opamp.


 
   
  Do you mean the output (NJM4556) op amps ? I am not sure if those are what audionewbi referred to. In any case, it is not recommended to "roll" the output buffers, unless you cannot get the NJM4556AD for some reason.


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## camui78

I just received the Objective2 from JDS Labs last night and had the amp plugged into the wall with the AC/AC power adapter all night to break in some new IEMS.  This morning, the power button comes on but no sound through the headphones.  I see in the included "manual" the batteries need to be recharged if I hear no sound.  Even though the amp was connected to power all night, why would the internal batteries or plugged in still not produce any sound?


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## jseaber

Quote: 





camui78 said:


> I just received the Objective2 from JDS Labs last night and had the amp plugged into the wall with the AC/AC power adapter all night to break in some new IEMS.  This morning, the power button comes on but no sound through the headphones.  I see in the included "manual" the batteries need to be recharged if I hear no sound.  Even though the amp was connected to power all night, why would the internal batteries or plugged in still not produce any sound?


 
   
  Does the amp work on AC power? All O2's are pre-charged.
   
  It's normal for O2 to disable output when the batteries are low. We test every amp twice (once on AC power without batteries, once again on battery power). So, this is most likely a power adapter problem.


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## audionewbi

Sorry to go off topic but is there any plans to redesign O2 so the volume and input/output is at the smaller side for better stacking and transport?


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## jseaber

Quote: 





audionewbi said:


> Sorry to go off topic but is there any plans to redesign O2 so the volume and input/output is at the smaller side for better stacking and transport?


 
   
  Want to help track down an anonymous blogger? New O2 development is limited by the state in which NwAvGuy/RocketScientist left his projects.


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## camui78

Quote: 





jseaber said:


> Does the amp work on AC power? All O2's are pre-charged.
> 
> It's normal for O2 to disable output when the batteries are low. We test every amp twice (once on AC power without batteries, once again on battery power). So, this is most likely a power adapter problem.


 
  It did work last night, but now the batteries and adaptar will play for a few seconds and the sound will have static and cut back off.  Not sure what the problem could be.  I assume the batteries are drained?? but this shouldn't happen with the power adapter plugged into the wall as well.


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## jseaber

Quote: 





camui78 said:


> It did work last night, but now the batteries and adaptar will play for a few seconds and the sound will have static and cut back off.  Not sure what the problem could be.  I assume the batteries are drained?? but this shouldn't happen with the power adapter plugged into the wall as well.


 
   
  Defective AC adapter. We'll send another.


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## Jazmanaut

I build Objective2 head amp kit, about 3months ago. I choose DIY version, because i needed to mod inputs and outputs for my studiopurposes.
Build was very straightforward and painless and first time that i plugged it in without any source and cranked volume all the way up, and heard nothing. Oh crap.
Hit gain switch, and still nothin. Uh, i must do something wrong. It´s not working. Well then i plugged source on it, and whoah, everything is just beautiful!
It´s just so silent, that it´s unbelieveble!

And how is the sound quality? 
It is very, very transparent. It does what amplifier should do, in my books: Amplify the signal. Nothing else. And boy does it do that well!
Tight and faithfull represention. No BS. Just love it.
Stunning noisefloor and channel separation, minimal distortion and enough gain for any cans. What else could you want? 
Oh and price is just ridicilous! I heard ten times more expensive headamps, that did not perform like this one. 
You really have to make an effort to find something better when we are speaking about pure performance, and forget about it´s price and the fact that it´s so small and lack of esoteric woods, and other highend bling.

And here is my finished product, in beatifully handcrafted enclosure, by yours truly:


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