The problem is that high-sensitivity ‘phones tend to be exceedingly revealing of even trace amounts of noise that may be present. This is where it would be nice if the EF-6 offered (as does Burson’s Soloist) a third low-gain setting that could help keep noise floors in check. This is not to imply that the EF-6 is noisy, because that’s certainly not. It’s just that having a third, lower gain setting could potentially help the amp better manage whatever noise it does produce in those cases where the EF-6 will be used to drive hyper-revealing, high-sensitivity ‘phones.
But please don’t misread us or give too much weight to our discussion of drawbacks, since all of them a relatively minor. The fact is that when looking for an amp that offers effortless reserves of power, considerable sonic refinement, and the elusive and desirable quality of musical naturalism, the EF-6 stands as a wonderfully engaging solution that is quite reasonably priced for the power and sound quality on offer.
For a tour de force show of many of the things the EF-6 does well try playing “Feeling of Jazz” from the Winton Marsalis Quartet’s The Magic Hour [Blue Note], with the EF-6 driving HiFiMAN’s own HE-6 planar magnetic headphones. This is a deceptively demanding track that features deep, powerful, and subtly modulated acoustic bass grooves supplied by Carlos Henriquez; delicate and almost lavishly detailed cymbal work from Ali Jackson; soulful and at times intensely modulated or inflected vocals from Dianne Reeves; and some downright spectacular horn solos from Winton Marsalis—including a few passages where he makes expert use of a wah-wah mute to almost literally make his trumpet “talk.” In short, there are a lot of distinct sound signatures vying for the listener’s attention, all them harder to reproduce than you might at first expect. Through many amps that attempt to drive the HE-6 ‘phones, the sheer sonic workload proves daunting, so that the track winds of sounding brittle, overwrought, or dynamically confused (especially when Reeves sings at full voice, or when Marsalis put the pedal to the metal with his trumpet). But when you leave the driving to the EF-6 you get an altogether different and better outcome. Every drop of hoped-for delicacy and detail makes itself felt, without any hints of discontinuity or sonic confusion when powerfully expressive moments come along.
But what really impressed me was the way the EF-6 took big dynamic swells in stride with almost casual ease, as if they were no big deal at all. Part of the beauty of this amp is that it makes handling multiple, complex, intersecting musical lines at high volume levels seem like the easiest and most natural thing in the world—just a walk in the sonic park. The freedom from unwanted edginess, strain, or compression is wonderfully liberating, again pulling listeners into closer contact with the music. Better still, the EF-6 imbues the HE-6 with some of its own relaxed, effortless-sounding sonic persona. Some audio journalists have described the HE-6 headphone as being prone to excess brightness, but in my view what they are really describing is the distressed sound of amps that don’t have adequate power to drive the HE-6 properly. The EF-6 amp, however, has more than adequate power, so that when teamed with the HE-6 the combination sounds extremely detailed, yet surprising smooth—a perfect recipe for naturally expressive sound.
There are, however, moments where the EF-6’s rich-sound yet easygoing sonic persona proves less effective than others. An example would be Musica Nuda’s live cover of the classic Beatles song “Come Together” as captured on Live à FIP [Bonsai Music]. Musica Nuda is an inventive and eclectic pop/jazz duet comprised of Petra Magoni contributing vocals (and free-form vocal embellishments) and Ferruccio Spinetti on amplified acoustic bass (which Spinnetti simultaneously plays as a melodic, rhythm, and at times as a percussion instrument). The net effect of Musica Nuda’s treatment should ideally be a heady mix of potent female vocals, expertly crafted melodic bass lines and grooves, plus unexpected and at time almost otherworldly vocal and percussive bass sounds—all driven forward by an almost palpable, electric energy. I played this track through the EF-6 and Audeze’s superb LCD3 headphones and found that the EF-6 caught all of the richness and textural complexity of the music, but was missing that elusive, three-dimensional sense of electric energy born, I suspect, of the interaction between the two performers and the crowd. As soon as the track was finished, I re-cabled the system and played the same track through the Burson Audio Soloist, again using the Audeze LCD3 ‘phones. While the Soloist’s rendition did not have quite the same quality of effortless power that the EF-6’s did, the Soloist’s superior ability to capture very subtle details and three-dimensional aspects of the sound helped restore the invigorating energy the track really ought to have.