This amp is awesome. Clean sound, with no distortion or hisses, (unless you turn its volume knob too high, or use the "High Gain" button, and turn the volume too high on that). It powers all of my headphones very well. The build quality is superb. It is robust, metal, and heavy. A solid piece of equipment, unlike many of these dingy, plastic, fragile amps from China. I use it on a Windows 10 laptop, or my old iPod Touch, etc. I often carry it around with me, and use it on it's batteries for about 5 hours each outing, no issues with the portability, (even though it is a big boy). A great Headphone Amp, I love it!

I use the o2 amp connected to an oDAC in my office and listened with a Beyerdnamic DT1350 for over 6 months, average 3 hours a day. There was a few days of breaking-in, then it is excellent. everybody I showed the combo to thinks it is too good. even compared to my sony ma-900 with Xonar STX. definitely a nice set up for indoor use. Tyler is very helpful and replies extremely fast. Great service.

This black box does exactly what it's supposed to; amplify! It does this well! I ordered the original design - without extra ports. Using it, I get zero interference from radiating electronics. Although it's by design, I also get no electrical AC buzz. There's a slight hiss on high gain with sensitive phones, but that is to be expected. However, it is far lower than with other aps I tried. Build quality is superb. Clean solder, good parts placement, sturdy rails to hold the PCB, and a tank like case gives an impression for being reliable and long lasting. 3.5 ports are solid! I have no worries hooking them up to jacks that stick out with coiled long cables. The slick black design goes great with the knob upgrade, and looks lovely on my desk. Supplied batteries have enough juice to last me for one workday if I turn it off while not using. The thing that impressed me the most was Tyler's level of service. He answers fast, and is willing to care for any issue. Headphones: DT770-250Ohm Player: Ipod Classic 7g (Lineout)