Vacuum tube headphone amplifier/USB digital-to-analog converter

  • HiFiMAN EF2A


  • HiFiMAN EF2A

    Angled back view

Item #: 818EF2

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Expected: 10/3/2014
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Our take on the HiFiMAN EF2A

by Dave Bar

Why buy a headphone amp?

High-performance headphones need high-quality amplification to perform up to their full potential. If you connect them directly to the headphone jack on your computer, iPod®, or stereo receiver, you may be disappointed. A separate headphone amplifier sends a stronger, cleaner signal to your headphones.

Add the magic of tubes to the sound of your music

Plug the HiFiMAN EF2A into one of your computer's USB ports and prepare to be impressed. This compact digital-to-analog converter/headphone amp bypasses your computer's built-in DAC and audio circuitry — processing your digital music files outside the noisy environment of your computer for far better sound quality. The EF2A's vacuum tube headphone amplifier brings your tunes to life, imparting smoothness and clarity. You'll hear more dynamics and detail that you can really savor on your headphones. The EF2A also includes an analog audio input so you can enjoy improvements in sound with another music source. This is one component that looks so cool, you'll absolutely want to show it off on your desktop.


HiFiMAN's EF2A sports vacuum tubes for cool looks and hot sound.

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  • uses two 6J1 vacuum tubes for amplifier input stage
  • Burr Brown PCM2702 digital-to-analog converter for high-fidelity stereo sound
  • durable metal chassis and front plate construction
  • external power supply included
  • USB (type B) input for connecting to a computer
  • supported sample rates: 44.1kHz
  • input bit depth: 16-bit
  • stereo RCA audio input
  • full-size stereo headphone output
  • recommended headphone impedance: 32-300 ohms
  • signal-to-noise ratio: 95dB
  • frequency response: 20-20,000 Hz (±0.2dB)
  • output at 32 ohms: 3V, 320mw
  • output at 300 ohms: 6.2V, 256mw
  • 5-11/16"W x 3-1/8"H (including tubes) x 4-1/4"D
  • warranty: 1 year
  • Our 60-day money-back guarantee

Hands-on research from the Crutchfield Labs (what are the Labs?)

Product Research
What's in the box?

Download owner's manual

  • Headphone amplifier
  • Two 6AK5 vacuum tubes
  • AC adapter with attached 56" cord (16V/0.8A)
  • 5' USB cable (with Type A USB on one end and a Type B USB on the other end)
  • Owner's Manual

Our Product Research Team

At Crutchfield, you'll get detailed, accurate information that's hard to find elsewhere. That's because we have our own in-house Product Research team — they open the box, verify contents, check the owner's manual, and record dimensions, features and specs. We stay on top of new products and technologies to help people make informed choices.


Overview: The HiFiMAN EF-2A is a hybrid USB headphone amplifier which combines vacuum tube sound quality with solid-state technology to deliver outstanding audio performance. The EF-2A has two inputs on the rear panel: a line-level CD input and a USB input. On the front, you'll find a 1/4" headphone jack, power switch, source switch (CD or USB), and rotary volume control. The EF-2A has a simple, but elegant, brushed aluminum faceplate and chassis.

Vacuum Tubes: The EF-2A uses two 6AK5 vacuum tubes (equivalent to the Chinese 6J1) at the input stage to significantly improve the condition of the source signal. The tubes have a flat frequency response and a high signal accuracy. The tubes are packed separately inside the box, so you will need to install them through the provided holes in the acrylic top panel. When installed, the tubes protrude approximately an inch.

Burr-Brown DAC: The EF-2A's USB input incorporates a Burr-Brown PCM2702E DAC (digital-to-analog converter) to improve the audio performance from your computer's headphone output. The DAC provides 16-bit/44kHz resolution, which is equivalent to CD quality.

Power Supply: The EF-2A uses an external power supply instead of one that is built-in. This keeps the size of the headphone amp small, and prevents noise generated by the power supply out of the chassis.

Key Components:

  • Volume Control: ALPS potentiometer
  • USB DAC Chip: Burr-Brown PCM2702E
  • Vacuum Tubes: Chinese 6J1 x2 (6AK5)
  • OP-amp: OPA2604


  • Input Impedance: 47k Ohms
  • Output Impedance: 32-300 Ohms
  • Output: @32 ohms: 3 V, 320 mW; @150 ohms: 6.2 V, 256 mW
  • Frequency Response: 20 Hz to 20k Hz (+/- 0.2 dB)
  • Signal-to-Noise Ratio: 95dB
  • Distortion: 0.2%
  • Power Consumption: <15W
  • Input Voltage: 16 volts AC, 500 mA
  • Power Supply: 110/220 Volts
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HiFiMAN EF2A Reviews

Average Customer Review:

5 people say:

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2 out of 5

Needs some reworking

Written By Peter John, Madison, WI on Monday, April 28, 2014
I bought this amplifier a few years ago and was generally pleased, except for one thing; the gain is way too high. In order to operate this unit at a listenable volume without dipping into the channel imbalance at the lower end of the volume knob, it's necessary to turn down the volume on the computer. Unfortunately, this decreases resolution and dynamic range, a compromise I should not be forced to make when using an outboard DAC.

At first I chalked this issue up to the efficiency of my Grado headphones, but I recently bought some Sennheisers that are somewhat more difficult to drive. The problem was still present, albeit less pronounced.

Again, I was pretty pleased with this thing. The build quality is great for the price point, and the sound is pretty good when used with my turntable and phono preamp. But, when feeding computer audio through the DAC or playing DVD audio through the RCA ins, the input signal is just too strong for the little thing. I believe this is also the root cause of some complaints I have read in other reviews about the bass/midbass range.

I plan to perform some modifications soon that should alleviate the problem. Unfortunately, HiFiMan was unwilling to part with their circuit diagrams so I'm going to have to find a schematic elsewhere or reverse-engineer the thing. I probably would have given three stars, had HiFiMan customer service been a little more supportive.
Great build quality for price, inexpensive entry point into tube amplification
Too much gain! Poorly built circuit can't handle the inputs it was designed for.
1 out of 1 people found this helpful
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5 out of 5


Written By Erik, Chicago, IL on Sunday, March 17, 2013
Crutchfield Customer Review (What's this?)
The tube amplifier is something I've always wanted to own but never had enough cash to actually venture into that market. The amplifier in this little guy is great. My headphones, Sennheiser HD-518's, now have the power to run free. My previous setup connected my headphones to the headphone jack on a receiver. This kind of setup lacked power which resulted in severe ear fatigue. This is why I bought this combo: to properly drive my cans. Now I'm able to listen, even at a high volume, for hours without any fatigue.

The tubes themselves sound great. I would allow at least 50 hours of burn in time before you actually make an opinion on them. I'm over 75 hours now and they're still burning in, but sound great at this point. Consistent, clean power provides crisp highs, warm mids, and pounding lows. I've listen to everything from singer/songwriters to blue to jazz to electronica and everything sounds great.

The DAC is great and is nothing more than I need. Most of the files on my computer are either 192/256/320 mp3 files. I also have a small collection of CD's stored on my drive. These are the albums I listen to the most. Honestly, if I'm working on some homework or browsing the web I can't tell the difference between Pandora, mp3's, and CD's.

I have encountered a small amount of noise when I scroll my mouse wheel. After some troubleshooting I found that this interference comes from my other devices and not within the amp. I repeat, this is not within the amp.
Tube warmth, power, design, and size.
Interference with other usb devices
16 out of 17 people found this helpful
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5 out of 5

Def worth it

Written By N703ick, Ashburn va on Wednesday, February 27, 2013
Crutchfield Customer Review (What's this?)
Very good for the $$. Do not let the sound at first bother you. It can be tiny and no bass at first. After about 25-40 hrs of burn in on the tubes it will sound amazing. The volume is crazy, I like it loud and if you do to this is for you.
Tube sound (need I say more), good volume level, solid build.
Giant wall wort transformer plug. That's about it.
5 out of 5 people found this helpful
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5 out of 5

A Super Headphone Tube Amp

Written By Plainswind, Idaho Falls, ID on Saturday, January 19, 2013
Crutchfield Customer Review (What's this?)
I picked one of these up because I wanted to experience the warm sound of tubes as well as having an amp dedicated to my headphones. This little gem works its magic with the music, movies and games that I listen to. The chassis is well polished and all components are built of sturdy material. The tube sockets are made of porcelain, which surprised me. The clear acrylic window lets you peer into the amp to see its inner workings. The components within are high grade and assembled neatly. (The capacitors and MOSFETs are not laying on their sides or at angles; resistors are installed neatly, etc.) Its tone was somewhat 'tinny' when first used, but over the several hours that I used it, its sound stage became true and full. (About 48 to 72 hours) The volume knob and switches are solid and the audio channels are nicely balanced. I have tried it on both Mac (Mountain Lion) and Windows 7 (64-bit) with no issues. The CD audio input works wonders as well. I have paired it with the Bose AE2 headphones. (I have also tried other headphones; the amp drives them all nicely.) Overall, the tubes add a richness to the sound as well as a delicate glow to the room. I'll be enjoying this little amp for years to come. Thanks to Crutchfield for their super support staff and as always, super service.
Small, yet powerful. Catches the eye and has a rich sound stage.
9 out of 9 people found this helpful
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4 out of 5

Nice looking piece

Written By JoshW, LEH, NJ on Monday, December 17, 2012
Crutchfield Customer Review (What's this?)
When I was browsing in Crutchfield's site, I spotted this little jem. I was looking for an amp for my headphones. I have this unit installed into my home entertainment system. The unit is displayed on my end table in the corner. It works great with my Bowers & Wilkins P5's. The sound is so clear and pure. I listen to alot of classical and jazz. The sound has improved from just pluging into my reciever, which is a Yamaha RX-V471. The sound is so rich and full of detail. The tubes give off a nice glow. The only cons I have with the unit is the usb connection. If you have a computer with terrible audio and your willing to make the HiFiman your primary sound card then fine. To warn you, there is no instructions and no drivers with the unit. You have to find the right suitable driver for the DAC chip installed in the unit. The owners guide has no direction, if you have issues just contact the manufacture. I use it as a direct connection to my entertainment system. It serves it purpose. Its great for late night movie watching and listening to music collection.
Looks and sounds amazing
USB DAC. No Drivers. Poor instruction manual.
14 out of 16 people found this helpful
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1 question already asked

Are any drivers needed for this? Or is it just plug in and go? Where I work, IT is pretty strict about external installations. Thanks! [ Sean  May 11, 2014 ]
6 answers
  • Hello, i own one and i am very happy with it. Nice warm sound with Tubes when they get warmed up. You can Plug and Play, Ez Pz! i switch it from laptop to PC with ease, it will automatically get drivers and will switch to default(if not, ez enough to set it) [ ALEXANDER   May 16, 2014 ]
  • It's just plug and go [ Derek   May 13, 2014 ]
  • I am using my HiFiMan EF2A mainly with my home audio system by connecting it's left & right audio connections to the tape connections on my surround sound receiver. I did connect my HiFiMan EF2A to my new Apple iMac briefly, just to see if it worked, and it did--no problem. The computer recognized it while it was plugged in and it showed up on the "Sound" page in System Preferences. I had to select HiFiMan to use it and then go back and switch to iMac Internal Speakers when I was finished checking the HiFiMan, however. I didn't have to acquire any drivers for it to function on my iMac, but it's a new model and I don't know if another type of computer or an older model might require them. You might try calling the maker of the computers where you work and ask them. BTW: According to reviews online, the HifiMan EF2A is supposed to be a very good choice, for it's price, and I think it looks really cool. Not sure about the audio quality yet because it is new. It sounds all right so far, but it's a tube model and I understand from reviews that you have to burn the tubes for a number of hours before it is broken in. The sound is then supposed to improve quite a bit. (Supposedly one can get a "warmer " sound with tubes, as opposed to digital.) Also I am told you can try different tubes, including vintage ones, to tailor the sound to your preferences. The Tube Maze folks online are very nice and can advise you on the world of tubes. Hope this helped- [ George   May 12, 2014 ]
  • Just plug and go Sean. The sounds are great! [ BRIAN K   May 12, 2014 ]
  • It is pretty simple: plug and play. No driver installation is needed. [ Ryszard   May 12, 2014 ]
  • You will have to download a driver for the burr brown chip. When I plugged it in it automatically downloaded much like any USB stick would, no real huge software program, just a driver. Any setup is done through windows sound panel. [ ERIK   May 12, 2014 ]

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For a more in-depth review and enhanced detailed information on the HiFiMAN EF2A, please visit the Crutchfield website product page (/ISEO-rccbcspd/p_818EF2/HiFiMAN-EF2A.html ).

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