[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.

 

[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.

 

[maverickronin]

Quote:

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.

 

[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

 

[estreeter]

Quote:

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

 
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. 

 

[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".

 

[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.

 

[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

 

[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. 

 

[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

 

[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. 

 

[goodvibes]

Quote:

 

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.

 

[goodvibes]

Quote:

 
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.

 

[stv014]

Quote:

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).

 

[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