HiFiMAN EF-6 Headphone Amplifier (Playback 61)

HiFiMAN Builds A Serious Heavyweight Contender

Playback has reviewed a number of HiFiMAN’s earphones, headphones, and even a mid-priced tube-powered headphone amp, but we’ve never seen a product quite like the new EF-6 amplifier ($1599) from the creative Chinese headphone specialist. We say this because the EF-6 is the by far the largest, heaviest, most powerful, and most expensive headphone amp the company has ever built and it is arguably the product upon which HiFiMAN bases its most serious high-end/high-performance aspirations.

Another key goal for the EF-6 is to provide more than enough power to drive HiFiMAN’s superb but notoriously difficult to drive HE-6 planar magnetic headphone. To appreciate this latter goal, it helps to know that the HE-6 is, in principle one of the four or five best-sounding headphones we’ve ever heard, but it is also a headphone that precious few listeners had ever heard at its best, simply because it is so hard amps capable of properly powering the ‘phones in the first place. Having created the need for a great sounding an ultra-powerful amp by introducing the demanding HE-6 headphone, HiFiMAN now hopes to answer that need with the EF-6.

The bottom line is this amp is meant to compete with all comers, regardless of price or provenance, in terms of power output and sound quality. Given the plethora of worthy competitors now appearing on the scene, this is of course something easier said than done. Is the EF-6 up to the task? That’s the question we will try to answer in this review.

FEATURES

• The EF-6 is a Class A, solid-state headphone amplifier that puts out a whopping 5 Wpc at very low distortion (<0.03% at 1W @ 1kHz).
• Three switch selectable single-ended stereo inputs (two supported via stereo pairs of RCA jacks on the rear panel, one supported via a 3.5mm mini-jack on the front panel).
• Two stereo headphone outputs (implemented, respectively, via a very high quality, locking ¼-inch phone jack and an also very high quality 4-pin XLR-type jack).
• Two switch-selectable gain settings implemented via a rear panel mini-toggle switch. This feature addresses the fact that the HiFiMAN HE-6 planar magnetic headphone is roughly 10 dB less sensitive (or more) as compared to most competing headphones. In our experience, then, the high gain setting seemed to work best specifically for the HE-6 (or other similarly difficult to drive headphones), where the lower gain setting worked better for most other moderately easy-to-drive loads. As always, to minimize noise the best plan is to use the lowest gain setting that can produce adequate volume with the ‘phones at hand.
• The EF-6 provides variable-level preamp outputs implemented via a stereo pair of RCA jacks.
• Massive and robust build quality: the EF-6 is both larger and heavier than many stereo integrated amplifiers we have seen, in part because it sports an enormous internal power supply, with Class A MOSFET output devices that dissipate heat via huge, ribbed heat sinks stretching from the front to the back of both the left and right sides of the chassis. As you might expect, the unit runs quite warm to the touch, but never gets unpleasantly hot. The amp weighs approximately 24 pounds and exudes a rugged “overbuilt” feel.
• The EF-6 volume control provides a precision stepped attenuator for optimal sound quality, accurate channel tracking, and low noise.
• The amp features high-quality parts throughout.
• Two-color status indicator light:
  • Off = amp is powered down.
    Purple = amp is powered up, but still in initial warm-up phase of operation.
    Blue = amp is powered up, warmed up, and ready to play.
• Styling: The EF-6 features what might be called an “industrial chic” design motif, with most of the chassis metal work finished in a matte/crinkle-finish black. The EF-6 sports a thick, acrylic faceplate finished in gloss black with a recessed, matte finished center area surrounding the amplifier’s massive volume control knob.

Caveats

• The EF-6 arrived without a power cord (or any other accessories). Since the first thing we (and presumably you) want to do after receiving a new high-end amp is to plug it in and give it a test drive, we think HiFiMAN would do well to include one.
• Although billed as both a headphone amplifier and as a preamp the EF-6 does not include a remote control (nor is one available as an option), which makes the EF-6 less convenient to use as a preamp. We suspect HiFiMAN decided to forego a remote partly to contain build costs and partly to preserve sound quality (it’s harder than you might think to make remote systems that are noise free). Even so, we think HiFiMAN should consider offering a follow-on model that does include a remote.
• No support for balanced inputs. Given that the EF-6 is meant as the power plant for top-tier headphone systems and given the many high-end source components provide balanced outputs, it would have been nice for the EF-6 to include at least one balanced input. Note that this is a feature several new high-end headphone amps (e.g., the Bryston BHA-1) now offer.
• Our EF-6 arrived in a well-padded but nearly unmarked HiFiMAN shipping carton, and came without any documentation. Since world-class headphone amps deserve (and in a sense require) world-class packaging and documentation, HiFiMAN plans to address this problem soon. Our understanding is that current production EF-6 amps have begun shipping with manuals and in properly labeled cartons—two steps in the right direction.
• Revision control issues: The EF-6 has been in development for more than a year and over time we have seen prototype versions of the amp go through many iterations—some offering different features than others. Recognizing this we told HiFiMAN we wanted to wait until we could review the final, full-product version of the EF-6. Even so, our “production” EF-6 differed in several ways from the version shown on HiFiMAN’s web site. Specifically, our EF-6 provides a single rear-panel switch labeled “Gain”, whereas the web site version shows two rear-panel switches—one labeled “Feedback” and the other labeled “Operating Mode”. We have been told that our sample is indeed the final production model, but the fact that we had to ask underscores how important revision control discipline can be.
• Moving forward, we hope HiFiMAN adopts the time-tested practice of developing and then locking down good designs, and thereafter resisting the temptation to make further product changes until such time as the fim wishes to release successor products). Thip approach is desirable from both the manufacturer and customers’ points of view, because unit-to-unit consistency improves product serviceability and also enhances the product’s long-term value.