HiFiMAN EF-6 Headphone Amplifier

Editor's Note: Again I am so very pleased to welcome another new contributor to InnerFidelity's growing cadre of writers. Skylab is a long time member of Head-Fi (profile here) and has contributed numerous laudable gear reviews there. He'll be focussing his efforts here at InnerFidelity primarily on headphone amp reviews. I can't tell you how pleasing it is to find myself feeling more and more surrounded by a talented team of qualified reviewers. I'm stoked ... and humbled. I feel like I'm going to have to step up my game to keep up with these guys. Okay, I'll shut up now and let you get on with Skylab's review. Welcome aboard, mate!

The HiFiMAN EF-6 ($1599)
My first review for InnerFidelity, after having done many dozens of amplifier reviews on Head-Fi.org, did pose something of a challenge. The EF6 was designed to provide a partnering amplifier for the company's HE-6 planar magnetic headphones. The challenge was to write about the EF-6 and not about the HE-6. The HE-6 (my post on Head-Fi about the HE-6 is here) has been a difficult headphone for many people to get their arms around, and I believe the primary reason for that is their very demanding nature---they require far more amplifier power to sound good than just about any other modern-day headphone made. This is largely due to a quite low efficiency (published at 83.5 db but with no qualifiers, which makes the figure pretty well useless).

I initially thought that what people were saying about amping the HE-6 was overblown---until I tried them with a VERY powerful vintage stereo receiver, the Pioneer SX-1980 (which delivers about 27 wpc into the 50 ohm impedance of the HE-6 from its headphone out)---and this was for sure the best I had ever heard the HE-6 sound, and remains my reference to this day. (For those unfamiliar, the SX-1980 was Pioneer's flagship stereo receiver in the late 1970's, sold for $2,500 back then, and often fetches more than that today on the used market.) So I became a believer that the HE-6 need a lot of good clean power to really shine.

It's not as though HiFiMan doesn't know this---their original demo amp for the HE-6 was a Threshold power amplifier, driving the HE-6 from its speaker outputs. And this is how many people amp the HE-6 today---from the speaker taps of a stereo amp which is NOT envisioned as a headphone amp.

Slowly, however, as the HE-6 gathered a large following as a very top tier headphone (which it absolutely deserves in my opinion), "dedicated" headphone amps for it started to emerge. More accurately, these amps were designed to meet market demand for use with all of the relatively power-hungry planar magnetic headphones that have been gaining popularity, primarily from HiFiMan and Audeze. The EF-6 is HiFiMan's offering in this segment, which currently includes amps ranging in price from the Schiit Audio Lyr at $450 to the Ray Samuels Audio Dark Star at $4,000. Mercifully, the EF-6 is slightly more toward the affordable end than the Dark Star (which I thought did an excellent job with the HE-6), at $1,599.

I reviewed the EF-6 driving both the HE-6, and the Audeze LCD-3. I drive them from the balanced out of the EF-6, which offers 4-pin balanced and standard 1/4" headphone jack unbalanced outputs. Note that only unbalanced inputs are provided, but there are three switchable inputs two on RCA's around back and one 1/8" stereo mini on the front---a feature I like. The amp appears well made, looks nice but not exotic (which is also my preference), and is pretty heavy, weighing almost 25 pounds.

Source for the review was the Red Wine Audio Isabella Pro DAC, as included in the "Audeze Edition" DAC/Amp. I compared the EF-6 to the RWA driving the LCD-3, and to the Pioneer driving the HE-6.

Turn the page, and we'll have a listen ...


Frank I's picture

Rob excellent writeup and I thoroughly enjoyed the read an very happy Fang got the riight amp for the hE6 one of my favorite headphones. Nice job

Skylab's picture

Thank you, Frank!

Phos's picture

I thought the 4 pin output was a dual monoblack configuration.  

MacedonianHero's picture

Well done Rob. A great write up (as usual). 

Skylab's picture

Thanks, MH!

Phos, the front connector is a 4-pin XLR connector often used for "balanced" headphone wiring.

Phos's picture

It usually is, but I seem to recall reading that it's just like that for seperate grounds.   

thune's picture

The EF-6 prototype at RMAF 2011 had large attenuator steps. While perfect for the HE-6, it was impossible to dial in the desired volume when using it with the much more sensitive HE300 (which has similar sensitivity to the LCD-3). Does the production EF-6 amplifier suffer this issue with the LCD-3?

Skylab's picture

I didn't find that the steps were too course for the LCD-3, at all.  I had no issue there.  But for high sensitivity headphones, this amp would not be my first choice. 

As for heat, yes, the amp gets quite warm after having been on a while.  I wouldn't want to sit on it.

SERENDIB's picture

I have an EF6 from 2012 and both HE6 and LCD3 (and HD800), and the volume knob goes up in significant steps. I do find that I often like an in-between step and would have preferred a smoother movement especially for LCD3. 

zenpunk's picture

No mention of the switches at the back? particularely the feedback one and its effect on the  sound. How is the volume control? How hot does the unit gets? Can it be used with more sensitive cans? sad

Skylab's picture

I forgot to mention in the review that the EF-6 I received from InnerFidelity for the review actually has holes in the back panel for speaker jacks, and it has a headphones/speaker switch - but it is inoperative.

I found the effect of the feedback switch negligible. 

itsastickup's picture

Is the amp going to be measured? As much as some prefer subjective reviews, some of us don't want to put down so much money on such 'evidence' especially when one person's subjective review contradicts another's; which doesn't happen with measurements.

Tyll Hertsens's picture

I'll have Skylab ship the amp back here for measurements when they're ready.  Unfortunately we have to arraing for a chain hoist rental and some carpenters to box it up for shipment. :)

Just like me, Skylab's subjective experience is just one persons experience, though experienced subjects like he and I are few and far between. 

Willakan's picture

Give Tyll a chance! He hasn't even reported that he's finalised the amp measurement setup yet!

Tyll Hertsens's picture

Not nearly finished, but progress steadily made.

Can Crazy's picture

I don't know if you had the chance to measure John Grandberg's Violectric and Lake People Amps, but I guess hooking up the HE-6 on the EF-6 and the German Amsps would be an interesting comparison as well as reference on the challenges the HE-6 pose.

SHAHZADA123's picture

Excellent write up, as always.

Skylab's picture


attilahun's picture

Thanks Rob, great write up. 

Any thoughts on the EF6 vs the dark star?

Skylab's picture



Regarding the Dark Star, I did not have it on hand to directly compare, so I can't really make detailed sonic contrasts.  Both amplifiers drive the HE-6 very well, IMO.  The Dark Star is a fine amplifier, but undeniably a big part of the purchase price is made up of the very fancy casework.  My personal opinion (and it is nothing more than that) is that the EF-6 is a better value, if one is relatively unconcerned about the aesthetics of the amps (although I do not consider the EF-6 to be unattractive at all, just not fancy or exotic looking).  The Dark Star is much prettier though, and also does the job well.  It's nice to have choices ;)

attilahun's picture

That makes perfect sense to me. 

Plus the hifiman has lower labor costs I suppose. 

Looking forward to your next review. 

HeadphoneAddict's picture

Rob, I enjoyed reading this as usual.  I also think the EF6 is a great amp for HE-6, and want to add that it's also pretty good with my HD800, LCD-2 ande HE-500 as well.  Prior to the EF6 I was using my Marantz 2240 speaker taps with the HiFiMan speaker adapter to drive the HE-6, but the EF6 is an improvement in refinement, soundstage and micro-detail.  Power levels are close, with a slight edge in favor of the Marantz, but the EF6 power is enough to make almost anyone with HE-6 happy.  Thanks for the writeup!  I posted my impressions on head-fi.org in the Iron_Dreamer review thread.

Skylab's picture

Thanks Larry! much appreciated.

Sweden's picture

Do you get that tube amp holographic imaging using this amp?

Have you tried running the HE-6 from the CS300's headphone out/speaker taps?

Skylab's picture

Imaging was very good, but a bit short of the best tube amps in that regard.

The headphone out of the Leben CS300 really doesn't have enough juice for the HE-6.  I did use the speaker outs for a while, which I thought sounded excellent, but I had read that this might cause long term damage to the Leben's output transformers, so I stopped.


armandmarius1's picture

I have attached Audio technica headphones to the HiFiMAN EF-6 amplifier and all I can tell you is that I never heard such a clear sound, I like that the bass is a little sharper than other amplifiers. At this price you cannot find a better alternative, the guys from Hifiman made a very good job and their products are one of the best amplifiers found on the market.