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Positive Feedback ISSUE 68
Mjolnir Headphone Amplifier
as reviewed by Al Chieng
In an ever complex world of global economics, one must make choices about what business model will be most successful. For the consumer it comes down to choices; be they brand name, price, origin of the manufacture, etc., we ultimately make the dollar vote. The producer tries to accommodate this and it is through innovation, and sometimes a little luck, that we see companies succeed. I am a sucker for the little guy that tries to bring something interesting to the market and does not necessarily have the regular run-of-the-mill goals in mind.
My journey began with the obligatory search on the internet. I was looking for a solid state headphone amplifier and DAC to complement my system. I kept coming back to an amusingly named company called Schiit Audio, founded by two audio industry veterans who have created products that do not necessarily fit the common mold. The uncommon part of this company lies in a number of key aspects. First, Schiit builds all of its electronics in the United States. Second, they do not offer any special promotions or sales, offering instead one price to all customers while passing the savings, according to sales literature, to everyone. Third, instead of coming into the market with a state-of-the-art, cost- no-object kind of product; they have slowly developed a catalog that caters to many individuals looking for better sound, but with a definite budget.
Enter Thor's hammer, or the more aptly named Mjolnir (I also received the Gungnir, but this article will focus on the headphone amplifier, so stay tuned). For those who do not know what Thor's hammer is I cry geek tears for you. [Editor's Note: Mjolnir is the Norse name for Thor's Hammer, a weapon so powerful it could level mountains.] The Mjolnir is a solid state fully balanced amplifier that claims to be an "end game" amp with a relatively low price point. The topology of the amp can be found on the Schiit website, but I was curious and asked co-founder Jason Stoddard what went into the design process. His reply is as follow:
"Lots of hours and many mistakes. Or, more seriously, a lot of critical choices relating to the end goal, which is discussed below.
When we started the Gungnir/Mjolnir project, we went into it aiming to create products you could comfortably consider "state-of-the-art," without the ridiculous price tags associated with most state-of-the-art projects. Bringing that in at lower cost entailed a complete re-think of what we were doing at them time, which was relatively inexpensive (but well-received) components.
In the case of Mjolnir, we always knew we wanted it to be a balanced design. Balanced amps, though, usually have one or more drawbacks that compromise balanced operation. They're usually "bridged" amps, where one side is driven by the inverted signal from the other side's feedback—with a different gain structure. Other balanced amps simply don't output a balanced signal if driven single-ended, a pure approach, but not ideal, in our opinion. Still others, using Nelson Pass' "supersymmetry" topology, are truly balanced amps, but at the cost of low-input impedance and possible interaction with the volume pot, without buffers in the signal path.
This led us to a very old topology—the Circlotron. This inherently-balanced topology offers significant benefits--not only bypassing the limitations of other balanced topologies, but also allowing us to use only N-channel MOSFETs. N-channel and P-channel MOSFETs in a conventional output stage don't match exactly. An all N-channel design sidesteps that nicely. Also, we were able to use only a single voltage gain stage, for a very simple amp that still offers excellent measured performance--even without overall feedback.
Of course, Circlotrons require heroic work on power supplies, and cannot be "made" single-ended. So this meant Mjolnir would have to be a balanced-only amp. No single-ended headphone outs, and no RCA outs for the preamp, either. Adapters are a no-go. We considered this an acceptable trade-off to get "end game" balanced performance, at a price that doesn't make the wallet bleed.
High power was a given, with the current popularity of orthodynamic designs--which means Mjolnir drives pretty much anything on the market, including the HiFiMan HE-6. It's also quiet enough to be used with IEMs (with balanced cables, of course) thanks to a very exotic, low-noise gain stage JFET, which I believe we purchased the world's supply of. It's out of production, but we have enough to make a decade's worth of Mjolnirs (and in the process of developing Asgard 2, we've found some alternatives for when we're out of stock.)
In the case of Gungnir, the design process entailed the analysis of the currently available D/A conversion ICs on the market, a close look at the limitations of both computer and conventional transports, and—again—balanced. But not balanced like most inexpensive balanced DACs. We went for both full hardware balancing (two DACs per channel, one each per phase) and hardware summing back to single-ended to preserve many of the benefits of balanced, even with single-ended output.
Then, to keep costs down, we wrapped both Mjolnir and Gungnir in simple chassis with a minimum of ornamentation and gewgaws. No displays, no touch-screens, no integrated preamp functionality on the DAC, nothing but what you need. This is the main compromise we made to keep cost from soaring."
Thus, the design process done by the Schiit team has been intricate and well-conceived. Although the headphones I currently have are not what you call power hungry, my Audeze LCD 2 and 3 headphones did benefit from a little extra juice and from the balanced topology of this amplifier.
I was pleasantly surprised with the understated industrial design of the product, really simplicity at its best, and although solidly built, the unit was still very manageable to move around through the entire review. I used my LCD 2s and 3s as well as a highly modified pair of Grado SR 60s. The Mjolnir has a soft start feature, something I believe all amps should have to prevent the dangers of the initial power turn-on process. The front consists of a smooth volume pot and connections for either four-pin XLR balanced, or two three-pin XLR balanced configurations. The back is where the flexibility comes in. The Mjolnir has balanced and unbalanced inputs as well as a balanced pre-out. This makes the amp a possible preamp in a system. What I also like is the possible upgrade paths that the back of the amp presents in terms of what type of DAC you may have, or what you may want in the future. The required IEC socket and on /off switch are located on the back plate as well. Although through the entire time of my review I encountered no mechanical problems with connections or switches, if I were to nit-pick I would have installed a beefier on/ off toggle.
This amp is not for you if you require a fuller, warmer tone. Although highly capable through and through, it was not smooth and syrupy. I found at times the amp can be a little grainy at the extreme top-most treble region. Since most music happens in the mid region of the frequency spectrum I never really sweated the small stuff. In addition, instrumental music could have had more separation, but I was brought back down to earth by the very reasonable price tag (for a state-of-the-art component) and the strong attributes that this amp brings to the table. Schiit was not kidding when they said power, and the volume pot barely got past 9 o'clock. I think for most headphones a wider gain adjustment would make this amp even better.
The Mjolnir, paired with my Cambridge DacMagic and hooked up to my home office system, sang with a very dark background. Music and vocals came out very clear with no hint of hiss or hum. Although not a real-world test, the anal-retentive side of me likes to play "no music," and raise the volume on the device simply to hear if there is any noise generated by the amp; the answer is quiet on all fronts. I started out listening to some female vocals, and queued up the song "Deep Water" by Jewel, from her album Spirit. The amp presented the music with a lot of clarity, and I believe it resolves quite well in this manner, showing you the quality of your recorded material. Jewel's voice was well portrayed, and the pop singer's intonations and emotions were heard and felt. Getting involved with the music is important, and I found that whatever music I played through the Mjolnir, it pulled me in. One of the amp's strengths, besides the dark background, was keeping up the rhythmic pace and timing. For that test I listened to Jamiroquai's "Virtual Insanity" from Traveling Without Moving and got involved with Jay Kay and his acid jazz brand of music. The amp did not miss a beat, and gave believable presentation of his voice coupled with his eclectic ensemble. The backbeat of this song is infectious, and lesser amps have had trouble mixing this with his voice to form a cohesive whole.
Fans of electronic music will not be disappointed, as my next track took me to "The Game Has Changed," from the Tron Legacy Soundtrack. Daft Punk strikes again with authority and a unique sound that the amp captured. Strong swings from high to low are heard throughout, without breaking up, and showed this Schiit has the power to drive the changes. Guilty pleasure time was in order, hearing the magnitude of the bass portrayal, I threw in Dr. Dre's "Nuthin' But A G Thang" to hear the mid to high bass. Studio produced to bring out the mid to high bass, I found it entertaining, but not out of control. Vocal flow from Dre and Snoop Dog (Aka Lion) was never stifled, and I half-wished I could travel back in time to counsel myself on improving my car stereo all those long years ago. I guess nostalgia brought me to The Faces "Ooh La La" from their last studio album by the same name. The simple arrangement highlighted the range of genres that this set-up was able to portray. Light and upbeat vocals were accompanied by various instruments which were solid and honestly reproduced by the Mjolnir.
In the end, this amp gives you the tools to make up a serious listening package. Schiit Audio definitely put time in creating something that is capable of making someone happy for the foreseeable future. What is even better is that both guys are determined to provide the best customer service and support. The added forward-thinking of additional chassis space for upgrades proves they intend not to leave their customer hanging when the upgrade bug hits. Thor's hammer delivers and strikes a blow for those looking to go balanced and have a sneaking suspicion that a little more power is necessary to make your headphones come alive. Al Chieng
Mjolnir Headphone Amplifier