Roth’s vacuum tube amp improves iPod tunes… most of the time.

Like X-ray glasses and sea monkeys, vacuum tubes are the stuff of 1950s pulp-fiction cool. They even glow in the dark! And it turns out that they can improve the sound of modern digital music–if you stick with high-quality, lossless files, that is.

When you unpack Roth’s Music Cocoon MC4, a vacuum tube amp with a built-in iPod dock, you’ll get plenty of warning that this is the kind of fancy audio gear that’ll sniff at your lowbrow 128kbps MP3s. You’re greeted with a pair of white gloves to wear while handing the MC4, lest your sweaty palms taint its brushed aluminum surfaces in their excitement. We laughed, then enjoyed it as the kind of creative extra that takes a little sting out of the MC4’s sky-high price–it lists for $750, but we’ve seen it go for well under $500. (The gloves are also necessary should you ever need to handle the vacuum tubes, which are safely ensconced under an enclosure that protects them from everyday contact.)

The MC4 is a breeze to set up–you can drop in any iPod with a Dock connector (or an iPhone 3G or 3GS in Airplane Mode), wire up a CD player (via stereo RCA jacks), or connect a third audio source to its 3.5mm input. Its overall look is very British in its sturdiness (Roth is based in England)–no swoopy Scandinavian curves, just beefy knobs on a very classy casing. The MC4’s remote must be used to power it up, which is kind of annoying, but fortunately the remote also controls an attached iPod/iPhone. Just don’t plan on making this a centerpiece on a display table or mantle because the MC4’s big honkin’ power brick gets pretty hot and needs to be stashed roughly 2–3 feet from the MC4. Its cord is that short.

The star of the show, the vacuum tubes, emit only a faint red glow in a well-lit room, and while the effect was substantially cooler in a darker setting, it was never as dramatic as it seems on the MC4’s box or website. But sweetening your music is the primary function of those tubes, and that’s where they do their best work. The MC4 definitely warms up music of all types, reducing that digital brightness and making your tunes sound richer and more detailed. It’s not a transformative difference–it’s an audiophile’s improvement, rather than something that’ll leave you gaping in awe at newfound textures. Jazz in particular really shines on the MC4, but there’s plenty of power here to drive music of any kind at ear-shattering volume, if that’s your thing.

There is, unfortunately, a catch. When playing some 192kpbs AACs with thumpy, deep bass (Vampire Weekend’s “A-Punk” and Sade’s “By Your Side”), the MC4 completely barfed, spitting out a buzzing, distorted sound that was just like a damaged woofer trying to keep up. The problem vanished when playing those songs on the CDs the AACs were ripped from and reappeared when running the AACs through different speakers, proving that the MC4 can’t cope with some medium-quality rips. Other AACs of the same caliber played just fine, but it’s an odd flaw that points out how the MC4 tries to appeal to both audiophiles, who would never listen to anything but lossless music, and the general iPod crowd, who will be dismayed that the MC4 fails to process their run-of-the-mill rips.