Review on Portable Headphone Amp With 3.5Mm Stereo Audio Out, GAIN Support & Lithium Battery - Compatible With IPhone/Cellular Phone/MP3/MP4 /Computers. by Cody Bowie

I haven't really given it a good test, only a brief one, but it seems good enough for the average person. I can't do harmonic distortion tests or anything an audiophile might want to know about it but it didn't seem to clip when on full volume, and the volume was loud at the highest setting.If your phone or other portable device distorts on higher volumes, this might be worth getting. It's about the size of a small phone, rechargeable, and has decent sound. It's not going to be as loud or as perfect in sound as a tube headphone amp using 12AT7 (or 12AV7) tubes but it's also not going to require a wall plug. This is a portable headphone amp, not a desktop one.