I just bought the new O2 (the one with no battery and with RCA/ power/ input on the back) from headnhifi.com in Switzerland, because I live here.
i can make some photos if you want, but you can find them here http://www.headnhifi.com/O2-desktop-amplifier
I'm quite happy, this is my first headphone amp and I was skeptical: turns out the difference is quite noticeable. But onestly, I'm more surprised by how good it looks than its sound . Anyway, now my chain is complete and I'm happy of its sound.
I use it with the HE400 from hifiman.
I'm just curious of 2 things, I'm sure you can answer me.
1) Should i leave the jack in when I turn on the amp ? And when I turn it off? Should the volume be down to zero?
2) The Odac light is always on, even when my pc is off, will this ruin it? How do you turn it off?
And, just as a curiosity, for those of you that have the he400 with this amp, is 9'o clock a safe listening volume (with low gain). At what volume do you listen? I already have tinnitus on cold months (every year), I don't want to damage my earing :D
1) As with any audio amplifier, to save any thump in your speakers/headphones and to save your own ears, especially if you accidentally left music playing and the volume is at full when you turn it on; you should always turn the control to minimum when turning it on or off. (Always was a good idea when I was doing stage crew at university!)
2) As it appears you bought the mains powered version of the amp/dac combo, I think the LED on the front is the power indicator for the O2 amp section only and the ODAC board inside is powered from the USB on your PC. So you should be fine.