The latest in a long line of affordable headphone amps from the Chinese manufacturer, the new E02i is a minimal, portable-specific device (the 1/8-inch cable is permanently attached, and the housing sports an integrated belt clip). It even works as an Apple remote play/pause and volume control, even with the headphone amp section's power off — a nice touch if you've got an iDevice and your headphones don't have an Apple-friendly mic/remote pod, though your mileage may vary with Android devices (pause/play worked on my HTC Amaze, but not the volume controls). If you've already got these functions on your headphone cable, you might find these to be overkill, but since most folks pick up headphone amps in the first place to use headphones that weren't designed to be "portable," I think it'll be much appreciated.
So does it fill a need? It certainly provides more juice for your cans, and made the HiFiMan cans a lot more usable with my HTC and Samsung handsets and my iPad2, though it doesn't seem to be as clean sounding a circuit design as other FiiO amps I've used. In a quiet environment, the gentle volume boost introduces a noticeable amount of background hiss; especially so with sensitive IEMs. On the subway, bus, or in an airplane cabin, of course, you won't notice this at all, so this (mild) criticism is probably beside the point.
As for that bass boost switch, I felt that to my ear — assuming a good seal with a given pair of headphones — turning on the Rocky's bass boost gave me a tad too much of a low end boost for a lot of rock, pop, and jazz, even on the subway or out on the street — the effect seemed too broad, coloring the midrange a bit for my taste. I found myself thinking that an intermediate setting, or some sort of trim control would be handy here, since unless you're listening mostly to stuff with a lot of pure sine wave synth bass, you might not enjoy the somewhat synthetic effect. But In the right context, it worked well.
It turns out that sometimes you really do more low end than your cans can provide on their own — I queued up an old favorite, "Nephatiti" (from 808 State's ex:el), and thought the mix — heavy on synth bass and tuned drum machine kicks — benefited from the Rocky's nice club system punch. Working through the Sol Republic models, I enjoyed the effect on the relatively bass-light v12s, didn't think it was really necessary on the v10, and I could pretty much do without it on the big-bottomed v8.
However, something with a more clinical mix — Autechre's "Rpeg", from EP7 — wasn't helped by the Rocky, using the relatively bass-forward V-Moda M-80. The already boxy kicks became flabby, their attack lost in the murk. But on the following track, "Outpt," the bass boost lent the subsonic kicks some clubby authority.
The upshot (or down low)? If you've got bass heavy cans already, you might not need, or want to use the boost. Unless you really love low end.
Something a little more contemporary — Photek's "Totem" (from his 2011 Aviator) was a little more of a challenge, with the bass boost introducing some distortion on the already very forward kicks, but the sub-bass drones definitely had a lot more oomph. Think SPL-contest entry car stereo sub oomph. Which, in this case, is kind of a good thing. Classic sample based hip-hop ("Cold World," from Genius/GZA's Liquid Swords, for example) didn't do as well, with the bassline and kicks sounding bloated, distorted, and overpowering the vocal — but those records are based around recordings of actual instruments, albeit at two or three removes. Stick to the pure electronics, and you'll be fine. Maybe seriously dedicated bassheads would dig this regardless of program material, but I'll leave that up to you.
This obviously isn't an "audiophile" effect, but if you're into hip hop or electronic dance music and do a lot of headphone listening, something like this might be right up your alley. And come to think of it, isn't that presenting the music the way the artist intended?
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