I sold all my other amps, and have 2 O2's.
One I built and one from JDS Labs.
Went thru all the things being mentioned here and its a good discussion, but I am so glad that I discovered this little gem of an a amp and that it
performs so well.
I have gone back to the 'music' and playing around with different cans and recordings....
Its a really amazing thing to have such a great performer run off of two 9v batteries for hours...no AC issues or problems.....gone.
It works very, very well with 90+ percent of cans out there....
Now back to the music!