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Millet hybrid headphone amplifier
as reviewed by Ed Kobesky
Back in the 80s, when audiophiles began rediscovering tubes, most of us weren't interested in power amps—we would stick with our solid-state amps for years to come. However, companies like Luxman and (later) California Audio Labs discovered that sticking a few signal tubes into the preamp section of an integrated amp or the output stage of a CD player could ease the rocky transition from smooth-sounding analog to screechy digital.
Two decades later, it's still a good idea. Many audiophiles swear by their tube preamp/solid-state amp combos because they add the magic of tubes without the heat and hassle of biasing, swapping, and replacing power tubes. Headphone amps are no place for quads of KT88s or 6550s, yet many of us could use a bit of tube magic in our headphone rigs, as we tend to pair them with portable CD players, iPods, and other devices that need a bit of smoothing.
I have good news and better news about HeadRoom's latest addition to their Desktop line. The Millett Hybrid amp ($649; add $199 each for stepped attenuator and Home electronics module–see below) offers the sweet sound of tubes, and does so without going for an overly saccharine sound. Despite HeadRoom's promise that the Millett adds "a luscious wash of color" that will make "ragged and low fidelity recordings sound better," it thankfully does not go quite that far, offering the tight bass and high highs you'd expect from a solid-state design without doing much softening.
The tubes assert themselves in other areas. Compressed or closed-in recordings blossomed, with better air and space around the instruments. Vocalists in particular had a more lifelike presence. Nevertheless, bright recordings continued to sound bright, as did edgy, early DDD compact discs. I was using a pair of Grado's recently revamped SR325i headphones—a bright and unforgiving design if ever there was one—and the Millett did little to mitigate their tendency to grate over the long term.
Does that mean that the Millett Hybrid is a failure? Far from it! This is another in a long line of great headphone amps from the current masters of the art. Their addition of tubes is not a gimmick—the tubes added flavor and liveliness that brought me closer to the music. They won't turn chicken shit into chicken salad, but they will "open up" your MP3 files and older CDs. I also found the Millett to be an ideal partner for XM satellite radio. When I used it with my Audiovox XCS9 receiver, I found the somewhat dense sound quality of these digital broadcasts to be far more tolerable–even enjoyable.
The Millett Hybrid is based on a popular DIY design by its namesake, Pete Millett. Co-developed with HeadRoom's engineers, the unit incorporates a low-voltage tube line stage into a traditional solid-state architecture. If you are so inclined, you can also pass your signals through HeadRoom's built-in crossfeed circuit, which introduces a subtle time delay that creates the illusion of a more natural soundstage between your ears. I find it indispensable, but others may question the logic of passing their music through yet another round of electronics.
The Millett uses only one pair of tubes, but three pairs are provided: one each of 12FM6s, 12AE6As, and 12FK6s. According to HeadRoom, the Millett is designed to operate over a wide voltage range, so precise biasing isn't necessary. However, each tube has a slightly different comfort zone, so a front panel selector is provided. Set it to whichever tube type you're using and forget it. While you won't be likely to find these tubes at your local audio supplier, replacements are available if you look around. Best of all, they're cheap, ranging from around $2 to $10 apiece. You won't be replacing them often, as they will last up to 10,000 or more hours if treated with care. That means not switching them on and off too often. If you're going to listen throughout the day, just leave the unit powered up.
HeadRoom products are known for their commendable build quality, yet the older designs tended to look utilitarian. The new Desktop line exhibits flowing lines, and thoughtful touches like rubber bumpers on vulnerable corners. The Millett's front panel features both quarter- and eighth-inch headphone jacks in addition to switches for power, crossfeed, gain, and tube type. A rear output is also provided, which can be switched on and off from the front panel. This means that the Millett can also be used as a preamp, and two inputs are provided around back. Unfortunately, switching between them is also done from the back.
Like most HeadRoom products, the Millett has a certain charm to its customizable nature. Not only can you swap tubes, but you can specify factory-installed options like a stepped attenuator, an upgrade from "Desktop" to "Home" electronics, and a separate power supply. I used the Millett in stock form, swapping tubes and having a heck of a good time. A tube cage is not available, but there's really no need—the tubes run cool enough that you could probably touch them with your bare hands (which you really shouldn't do—use latex or cotton gloves when handling tubes). Most people will want to try all three sets of tubes, and a cage would only get in the way. I didn't hear major differences between tube types, but you may prefer one over the others.
That brings me to my sole annoyance with the Millett. The tube sockets have a very loose grip, which makes tube rolling easy but makes it very easy to dislodge them. A quick swipe of a feather duster, or a small jolt, is all it takes to break contact. I checked the tubes before each listening session to be sure they were properly seated, and they often weren't. It is also necessary to be gentle when installing tubes, to make sure that they're upright and fully seated. They aren't inserted in the sockets so much as resting on top of them. Pushing hard can do damage.
During most of my listening time with the Millett Hybrid, I used my Sennheiser HD580 headphones. Sources varied from the aforementioned Audiovox XM tuner to a Samsung DVD player feeding a Firestone Audio DAC. The results were outstandingly musical. The Millett Hybrid is quiet, though not as black between the notes as a pure solid-state design like HeadAmp's Gilmore Lite. However, the Millett sounds somewhat friendlier over the long haul. Sennheiser headphones have always impressed me by being both physically and aurally comfortable, so combining them with an expressive tube amp like the Millett was an ideal match, at least for me. The pair never sounded clinical, and I never got the sense that music was being hurled at me. Every performance occupied a palpable physical space, and did not sound like it was pressed against my ears.
While the Millett Hybrid isn't overly syrupy, it is less source-dependent than other headphone amps I've tried. It was quite forgiving when I tried it with a cheap Sony DVD changer in my bedroom and a battered Discman at work. Because the tubes are somewhat vulnerable, I never found it ideal for a bedside table or my cluttered desk. I prefer to think of it as an adjunct to my main rig—a compact, audiophile-level entry into the world of private listening.
There are many good headphone amps being made today. I've heard great ones that cost as little as $200. Starting at $649, the Millett Hybrid is a bit on the expensive side. I'd be nervous leaving something that valuable at my office, but it is ideal at home. It sounds "tubey" enough to make listening fatigue-free, yet it does not sound cloying. It is also roughly half the size and price of my all-time-favorite integrated tube amp, the Prima Luna ProLogue Two. If you like one, chances are you'll like the other. Ed Kobesky