The O2 is a bit of an 'odd duck'. It was designed as a 'concept amp' to illustrate how much performance could be designed into an amp per dollar. It is still competitive in its price category although alternatives have emerged (Atom, Heresy). Every aspect of the design- right down to all connections and controls being on the front panel- was chosen to make the 'bottom line' as small as possible while meeting performance goals.
By 'odd duck' I am referring to design compromises that were made. Virtually all of these compromises were the result of the (IMO ill-considered) decision to adopt portability and rechargeability as design goals. It simply isn't a very good portable due to it's size and weight.
The compromises made to support portability, mainly the power supply, compromise operation as a desktop unit. The PCB space allocated to the batteries- roughly a third of the board- could have been used to provide space for circuit improvements and/or to space the parts out more for easier assembly by the DIY crowd. I bought the agdr 'Booster Board' for mine which replaces the entire output stage. I intended to install it myself but quickly dropped those plans when I opened it up and saw how crowded the board was. I sent the Booster Board (and the amp) to agdr and he put it in for me. Sadly, agdr has now gone into hiding just like NWAVguy so he isn't around to help with things. They are both still around, somewhere, because their websites are still up.
One thing about the O2 though- it is customizable in ways that most amps (whether ready-made or DIY) are not. I was able to 'dial in' the gain for both my sensitive 45Ω IEMs and my harder-to-drive 250Ω full size cans. You can't do that with anything pre-built and I'm not aware of anything DIY/kit that does it either. (The 'WHAMMY looks promising if you don't need to drive sensitive IEMs, but you will need to 'engineer' an enclosure.) The O2/agdr amp is dead quiet and has good volume control range with both these very different loads. Too bad NWAVGuy disappeared before releasing the desktop-only counterpart which was well along in development according to his website.
Lastly, one of the goals of the O2 was to change the conversation about headphone amps and compel manufacturers to raise their game in the areas of performance and documentation. That goal was met too, and the O2 IMO deserves some of the credit for the dramatic improvements we are seeing today, especially at the 'budget' end of the spectrum. I'm shopping for a budget amp right now although I am not really 'dissatisfied' with my O2/agdr amp (Retail therapy? Perhaps.) Right now Im leaning towards the Heresy because I just don't want a plastic amp.
By 'odd duck' I am referring to design compromises that were made. Virtually all of these compromises were the result of the (IMO ill-considered) decision to adopt portability and rechargeability as design goals. It simply isn't a very good portable due to it's size and weight.
The compromises made to support portability, mainly the power supply, compromise operation as a desktop unit. The PCB space allocated to the batteries- roughly a third of the board- could have been used to provide space for circuit improvements and/or to space the parts out more for easier assembly by the DIY crowd. I bought the agdr 'Booster Board' for mine which replaces the entire output stage. I intended to install it myself but quickly dropped those plans when I opened it up and saw how crowded the board was. I sent the Booster Board (and the amp) to agdr and he put it in for me. Sadly, agdr has now gone into hiding just like NWAVguy so he isn't around to help with things. They are both still around, somewhere, because their websites are still up.
One thing about the O2 though- it is customizable in ways that most amps (whether ready-made or DIY) are not. I was able to 'dial in' the gain for both my sensitive 45Ω IEMs and my harder-to-drive 250Ω full size cans. You can't do that with anything pre-built and I'm not aware of anything DIY/kit that does it either. (The 'WHAMMY looks promising if you don't need to drive sensitive IEMs, but you will need to 'engineer' an enclosure.) The O2/agdr amp is dead quiet and has good volume control range with both these very different loads. Too bad NWAVGuy disappeared before releasing the desktop-only counterpart which was well along in development according to his website.
Lastly, one of the goals of the O2 was to change the conversation about headphone amps and compel manufacturers to raise their game in the areas of performance and documentation. That goal was met too, and the O2 IMO deserves some of the credit for the dramatic improvements we are seeing today, especially at the 'budget' end of the spectrum. I'm shopping for a budget amp right now although I am not really 'dissatisfied' with my O2/agdr amp (Retail therapy? Perhaps.) Right now Im leaning towards the Heresy because I just don't want a plastic amp.
