HiFiMAN EF-6 Headphone Amplifier (Playback 61)

Headphone amps and amp/DACs
  • 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 firm wishes to release successor products). This 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.


Background: In our listening tests, we evaluated the EF-6 with ancillary components as outlined below.

Source Components:

  • Oppo BDP-95 universal/Blu-ray player, using the player’s dedicated, single-ended stereo outputs with signals fed via high-quality cables from Nordost.


  • Audeze LCD3
  • HiFiMAN HE-400, HE-500, and HE-6
  • Shure SRH1440 and SRH1840
  • Sennheiser HD800

The Sound: The sound of the HiFiMAN EF-6 bespeaks seemingly limitless reserves of power—even when driving HiFiMAN’s own HE-6 headphones—yet the amp in no way sounds slow, sluggish, or “muscle-bound.” This, I think, is one of the most appealing aspects of the amplifier; it offers locomotive-like power and drive capabilities, but with skateboard-like agility.

What does “power” sound like in action? In the case of the EF-6, the sound of power could be described as the cumulative effect of a hundred small sonic cues that tell you this amplifier is unfazed by difficult loads and is never working very hard—no matter how outlandish or extreme the dynamic challenges your music might present. Through the EF-6, vigorous transient sounds seem to hit a little harder without so much as a trace of apparent compression, while potent crescendos seem to expand in scale and impact without any discernible amplifier-induced limitations. Over time, then, you come to trust the fact that with the EF-6 in your signal path, the amplifier will never, ever again be the limiting factor in reproduction of musical dynamics. This is one respect in which the EF-6 deserves to be called a world-class amp.

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