Originally Posted by HiFi1972
If you had a mastering-grade DAC (clean, transparent) and wanted to build an absolutely transparent headphone amp that can drive headphones up to 800 ohms, what would you build?
Given that you're asking this question, an O2 would be a good starting point.
It's arguably distortion-free beyond the point of audibility.
The performance is verified on industrial-grade testgear (not the case for many designs, especially self-builds).
It will drive the very large majority of phones to adequate levels.
It's battery/mains operated
It's a comparatively easy build with all thru-hole components. Howto guides are being produced to complement the already comprehensive instructions. You can get help if you have a problem. You can easily replace the parts if you inadvertently destroy them. You can put NE5532s in it throughout as a temporary measure and it'll still work, albeit with reduced current drive capability
You can get a complete kit including enclosure from a group buy on DiyAudio.com.
It's probably the best value-for-money you'll get.
The Wire is a good amp by all accounts, but you will have to make decisions about a volume control, power supply and other complications. Better to leave it for a second build.
Discrete amps are complex, more difficult to debug, offer no significant performance advantage at these power levels and many are designed using no more sophisticated testgear than a soundcard + RMAA (if that). You could spend six months picking through specifications and still be none the wiser. Many are boutique merchandise (fashion items). As such, they will have their adherents, but who asks a fashionista for advice about comfortable hard-wearing shoes?
Bear in mind that beyond a certain point paper performance improvements are almost certainly inaudible (the amps sound the same).
If you're looking for a lo-cost, lo-risk, straightforward, hi-performance build, the O2 is the way to go.