Review: HiFiMan HE-6 Headphone and EF-6 Amplifier

Like wine, sushi, and plumbers, headphones can get a lot more expensive than most people realize. At Sound+Vision, we focus on under-$500 models. But when Dr. Fang Bian, the visionary entrepreneur behind the HiFiMan headphone company, asked if I’d like to try the company’s top-of-the-line, $1,299 HE-6 headphone and its new $1,599 EF-6 headphone amplifier, I thought it’d be a great chance to give our usual listening panel a sample of what only the most devoted and/or wealthy headphone aficionados usually get to hear.

We’ve thoroughly enjoyed our past experiences with HiFiMan’s planar magnetic headphones, including the HE-400 and HE-500. (See the HE-400/HE-500 review for a full explanation of planar magnetic driver technology.) But the HE-6 is scary. With a rated sensitivity of just 82.5 dB — 6.5 dB lower than the HE-500, which itself is challenging to drive — the HE-6 demands 4.3 times as much power. You can’t drive it with a smartphone or even with a mini headphone amp. All of which makes the HE-6 the kind of headphone you put on to sit back and relax at home.

No problem for the EF-6 amplifier, because it was designed to drive demanding headphones like the HE-6. It’s a Class A design. The elevator pitch for Class A is that audiophiles prefer it for its lower distortion, but it runs really hot and chews up lots of power.

Here’s the full story: In Class A, the amplifier’s output devices — transistors in the case of the EF-6 — are always conducting electricity no matter what the signal level. Because the transistors are always conducting, they’re always throwing off a lot of heat, which means they need big heat sinks. Class A amps also consume far more electricity than other amps. In the more common Class AB amplifier, the transistors stop conducting electricity when their bias voltage is exceeded. This creates what’s known as crossover distortion, as the signal “crosses over” from the positive transistor to the negative transistor or vice-versa. Depending on the way the amp is designed, this transition should occur only at relatively high volume, which would thus mask the distortion. But still, distortion is distortion. It belongs in guitar amps, not in hi-fi gear.

From the outside, the EF-6 is a simple device. Just three inputs: two pairs of RCA jacks on the back and a single 3.5mm input on the front, with a loop-through RCA output on the back. A two-position gain switch on the back is marked “0” and “10.”

The front panel hosts two different headphone outputs. One is the a ¼-inch stereo jack with a pro-style locking mechanism. The other is a four-pin XLR connector that carries a balanced headphone signal, in which the left and right drivers have separate ground cables instead of sharing one ground lead. Some headphone enthusiasts feel that a balanced connection delivers better sound. Using the balanced output requires headphones than can accept a balanced signal. Few can, but because all of HiFiMan’s full-size headphones have removable cables with a separate connector on each driver assembly, they can all be converted for balanced use with a quick cable swap.

The volume knob isn’t the usual potentiometer. Instead, it’s a 24-position rotary switch that switches individual resistors in and out of the circuit to control volume. This design allows high-quality resistors to be used for better sound quality and more precise matching of the left and right channels than could be achieved with a potentiometer.

Two downsides with this design. First, you can’t set volume quite as precisely as you can with a potentiometer; the steps are relatively large. And second, using that beefy 24-position switch made adding remote control impractical. Fortunately, because your headphones have to be connected to the amp anyway, not having remote control in a headphone amp isn’t such a big deal.

A couple of quick notes on the HE-6: It comes with a nice semi-hardshell nylon case, two sets of ear pads (one leather, one velour), and a balanced cable with a balanced-to-unbalanced adapter for use with standard headphone amps. Like the HE-500, it’s comfortable but heavy: Both weigh 17.7 ounces each.

Initial impressions

I’ve heard most of the high-end headphones on the market, so I had some idea of what to expect from the HE-6, but I was eager to see what our panelists thought of it. They’ve heard lots of very good headphones, including the HE-500, but nothing in the price class of the HE-6/EF-6 combo. So I invited two of our usual panelists, L.A. voice actress Lauren Dragan and jazz musician Will Huff, over to give a listen. I connected the HE-6 to the EF-6 using the balanced connection, then set up various other headphones (including the AKG K550 and Lauren’s PSB M4U 2) for comparison.

I’ve watched Will’s reaction to a lot of headphones, but never saw him so enthralled as I did when he put on the HE-6. “I don’t know if I have the vocabulary to describe this,” he said. “It blows me away how clean they sound. There’s no distortion at all, which really makes me want to listen. When the bass hits it has that perfect sense of the acoustics of the instrument, like hearing a live bass drum. My only disappointment is that the midrange is a little low in level, but I didn’t mind it because the highs and lows are so clean, and it all comes together beautifully. Short of being in the studio with the musicians, this is it. I really enjoyed the bass.”

As often occurs when we test large headphones, Lauren was put off by the HE-6’s weight. But she loved just about everything else about it. “It’s an accurate, clean, balanced sound,” she said. “The treble is extremely articulate and clear. I like the bass, but I’d like a little more bass — but maybe that’s just because I hear so many headphones with boosted bass.”