Periodic Audio Nickel headphone amp review: Make your smartphone sound like a high-res digital audio player

Periodic Audio’s Nickel portable headphone amplifier will break you of the habit of listening to music on headphones plugged into your smartphone, tablet, or laptop. And that’s how most of us listen to music these days, right? Dedicated high-resolution digital audio players deliver superior audio performances, but mobile devices are just so much more convenient—even when