Review: DigiZoid ZO2 and FiiO "Rocky" E02i Headphone Amplifiers

We've talked a fair amount in this space lately about how much of a difference a headphone amplifier can make in your portable listening. Whether it's correcting for out-of-whack output impedance or simply providing more juice for difficult-to-drive cans (here's looking at you, on-the-go planar magnetic fans), you can get a better experience for surprisingly little money, with a wide range of pocketable amplifiers on the market right now, ready to interface with your iDevices, Androids, and other portable media devices. Here we look at two interesting and affordable newish devices: the latest miniature amp from FiiO, the E02i, or "Rocky," and the latest incarnation of DigiZoid's unique ZO2.

Now, lots of apps and players include digital EQ controls, not too mention the psychoacoustic subroutines available from ventures like Dolby, DTS, Bongiovi, and SRS. And Beats has reinvented themselves as a supplier of software bass-boost algorithms for all manner of portable and luggable devices. But not everyone wants to fiddle with a touchscreen to adjust EQ, and not everyone likes the sound of the boost/cut controls baked into their otherwise beloved devices. Well, these devices from FiiO and DigiZoid have you covered, and then some.

The ZOin particular offers a dizzying array of tonal flavors, via a 32-postion tone control (I hesitate to call it just a bass-boost, for reasons I'll get to below), while the FiiO is a more workmanlike device, adding a bit of bass boost and extra juice, but also letting you not just use your hard-to-drive cans with your phone, but adding the iOS remote controls that are probably missing from your faves.

I listened to a variety of headphones, ranging from the relatively flat (several interesting pairs of IEMs we have in for review from Logitech and Westone) to the bass-forward (the Sol Republic Tracks, in V8 and V10 driver versions, as well as the flatter v12 version for comparison), along with a longtime low-end fave, the Beats Pro, in order to assess the effect on its own without interference from an already low-end heavy headphone. To see whether these amps provided enough juice to expand one's traveling headphone arsenal, I matched them with the just-barely efficient enough HiFiMan HE-400 and its big brother, the HE-500.