O2 desktop edition isn't working with my hd650s

I own HD650s and ended up buying the o2 amp, desktop edition. Whenever I plug in my headphones, they don't play properly. It's not just a hum or distortion. When I plug them in there's a pulsating noise, and when I try to listen to music, I can only hear like every other word. What is the problem?

Jan 26, 2017
I'm having the same issue. I read somewhere that it may be a power issue. I opened it up and put 9v batteries in, and the clicking went away. but after a day of use, the next day the clicking returned. which power adapter do you have? this is mine.
class 2 power supply model sp240 12 input 240vac 60hz output 12vac@220mA
Jan 23, 2017
Basic debugging steps: * have you tried other headphones with the O2? * have you tried your HD650 headphones with another amp (e.g. the headphone output on a phone or computer)?
I've had weird audio similar to what you describe when my DAC was not compatible with my computer (e.g. after MacOS updates that broke USB audio). But I would try the debugging steps above first.
Jan 23, 2017
I was mainly asking about the stuff plugged into the RCA plugs -- the 'source' of the music (which, I hope obviously, could cause the noises) -- but it sounds like you have eliminated the possibility that the problem is the source, since you get the pulsing sound with no source attached.
The basic approach is that you consider everything in the "system", and change one thing at a time, while holding everything else constant (no changes) to narrow down the possibilities of what could be wrong. Or you can try a single component in another system. The system consists of: * bad power? try a different outlet * bad power adapter? try a different power adapter, or try the same power adapter in another system * bad input cable? try a different input cable, or try the same cable in another system * bad source signal? try a different source, or try the same source in another system * bad O2 amp? try a different amp, or try the O2 in another system * bad headphones? try different headphones, or try the same headphones in another system
It sounds like you have narrowed things down to the O2, or maybe the power / power adapter. You might try using a different wall plug, or another O2 power adapter if you have one. But otherwise, I think you have narrowed things down so that it seems like the O2 is indeed defective.
Jan 30, 2017
*Corrections: input is the two RCA plugs output is the 1/4" plug

Ok so you are hearing this "pulsating sound" when nothing at all is plugged into the RCAs and the only thing there is the o2 amp, the o2's power adapter, and your headphones plugged in to the o2? If that is the case then it is likely the o2 amp is bad, though it could also be that your headphones are not being plugged in all the way and are shorting the connections out.
Jan 22, 2017
Try another set of headphones to narrow it down...?