Objective Reviews & Commentary - An Engineer's Perspective

March 10, 2011

FiiO E5 Headphone Amp

fiio-e5-boxedINTRO (updated 4/7): The little FiiO E5 typically sells for under $20 and is so small you barely notice it. It’s “Apple-Shuffle-size” small. And, despite the ultra slim metal package, it has a Li-Ion rechargeable battery tucked inside, volume control, and selectable bass boost EQ. They even wisely made it rechargeable from a standard mini-USB cable so you probably have a cable laying around already if you lose the one that comes with it.

FOOD INGREDIENTS: Ever watched any of those “chef shows” on TV? They give a team of chefs a simple assortment of ingredients and challenge them to make something amazing. The best chefs take common everyday items and create really tasty mouth watering entrees. That’s what FiiO has done here. This is in sharp contrast to certain “boutique” audiophile companies that take high-end exotic ingredients and combine them in ways that don’t taste very good. The difference, in my opinion, is engineering talent and resources.

To put this another way, a good French chef can do more with a few eggs, cheese, butter and a piece of bread than a bad chef can do with $500 worth of exotic ingredients. What good is including exotic ingredients if the entrĂ©e tastes awful? FiiO seems like they have a French chef on staff able to transform inexpensive parts into something that’s relatively impressive.

CLIP IT ON: Like the Sansa Clip+ (see my review) it has a built in clip (sexy metal even!) to help with cable management. So you can have your player in your pocket, and the E5 clipped to your shirt, or whatever might work.

OTHER FEATURES: For the price, the E5 impressed me as being relatively well designed. Here’s a link to the features & specs.

OPERATION: It has a small power button, EQ switch, and a volume up/down “rocker” switch. The volume steps are impressively fine with no big jumps and you can hold down the rocker to steadily increase or decrease the volume easily. You can also use it while it’s charging or just leave it plugged into USB power. On my PC I didn’t hear any extra noise using it on the wimpy headphone output while charging it from a USB port on the same PC. There’s a 3.5mm input and a 3.5mm output jack, the mini-USB charging port, and that’s about it. It comes with all the necessary cables. The LED indicates charge status when it’s re-charging. There are plenty of volume steps so you don’t find yourself wanting for finer resolution.

BASS EQ: The bass EQ subjectively is fairly pleasant, relatively subtle, and particularly welcome with headphones that have flat bass response (i.e. those from Etymotic, RE-1’s, etc.). With bass shy headphones it adds a bit of of “heft” without creating any boom. The curve is shown in the Tech Section but it’s about a 3 dB boost centered at 80 hz.

HISS & NOISE: For such an inexpensive amp, it’s impressively quiet. It doesn’t have much noise of it’s own. Even with my ultra sensitive Ultimate Ears SuperFi 5 Pro’s, the hiss at full volume with no input is barely noticeable. It will, like any amp, boost whatever noise your source device has. See my article on headphone amps.

SUBJECTIVE SOUND (updated 3/21): The E5 sounded impressively good for its size and price. It’s clean, clear, plays plenty loud, and has no issue with low impedance, high impedance or balanced armature headphones. I had no complaints with the sound.

QUALITY CONTROL? My E5 sample has a slightly audible 3.8 dB channel imbalance but only with the bass EQ off. And it’s relatively constant regardless of the E5’s volume setting. Many other E5 owners have confirmed this is not normal. So apparently I got a slightly defective one.

fiio e5 testMEASUREMENT SUMMARY: The good news is the maximum output level, output impedance, distortion, and most everything else was amazing for a such a small inexpensive amplifier. The frequency response was –3 dB at 20 hz which isn’t likely to be a problem but isn’t as flat as say the Sansa Clip+ either. And the noise was a few dB higher than I would have liked to see but still respectably low at around –88 dB. The distortion also climbs at very low frequencies but this isn’t likely to be audible as human hearing is not very sensitive to deep bass distortion.

BOTTOM LINE: This a respectable little amp for the size and price. It’s surprisingly well designed, well made and it performs much better than I expected. To put it in perspective, this little $20 amp easily outperforms the amp in the $130 NuForce uDAC-2 in several respects. It has a much lower output impedance, lower overall distortion across most of the audio spectrum and higher output into low impedances. The lower output impedance, in particular, allows it to deliver much better performance with IEMs that use a balanced armature, multi-driver, or similar technology (i.e. Shure, Etymotic, Ultimate Ears, Westone, etc.).

TECH SECTION (optional reading for more details):

THD & REFERENCE LEVEL: With approximately a 200 mV RMS input (which just about any source should be able to provide), I adjusted the E5’s volume control for 400 mV of output (a gain of “2X”) as this should approximate real world use. With a 15 ohm resistive load, here’s the result:

FiiO E5 1 Khz 200mV RMS input 400mV RMS output 15 Ohms THD & Balance (ref 400 mV)

The distortion of 0.01% is quite good. By comparison, for example, the NuForce uDAC-2 measures about 0.05% on this same test with the same load. What’s really not so good is the 3.9 dB of channel imbalance. This isn’t a “tracking” problem as it’s essentially the same at any volume setting. It’s just one channel has nearly 4 dB more gain than the other but, interestingly, if you turn the bass EQ switch on, it goes away (the channels are balanced). To measure the output impedance, here’s the same set up with no load. The voltage in Channel A went from 401 mV to 420 mV and doing the math, that’s a very impressive 0.7 ohms—that’s even better than I measured with the Sansa Clip+ and I thought it was impressive:

FiiO E5 1 Khz 200mV RMS input 400mV RMS output No Load THD & Balance (ref 400 mV)

MAXIMUM GAIN & OUTPUT: Here’s the E5 with its volume at maximum. I raised the input voltage until it was close, but not yet clipping. Here, even with 1.27 volts of output into 15 ohms—over 100 mW of output and the THD is still under 0.02%! This is very impressive. And 100 mW is a very impressive output level. This is about twice what the NuForce uDAC-2 could manage into the same load. Note also, this is referenced to the input voltage. So the maximum gain of the E5 is 8.5 dB in one channel and 4.6 dB in the other. I didn’t bother testing into a higher impedance load, because with the 0.7 output impedance it makes little difference. It always starts clipping around 1.3 volts RMS.

FiiO E5 1 Khz 480mV RMS input 15 Ohms Max Volume Output & Gain (ref 480 mV)

INPUT CLIPPING THRESHOLD: To measure how much signal you can drive the E5 with, I gradually raised the input voltage until clipping was detected with the E5’s volume turned down. The answer is a lot! it didn’t start to have a problem until around 760 mV RMS:

FiiO E5 1 Khz 750 mV RMS in 15 Ohms (unity gain) THD Input Clipping Threshold

THD SWEEP: Here’s the THD swept versus frequency for both channels. The lower traces (red and yellow) are with no load. The upper traces (blue and gray) are with a 15 ohm load. The distortion rises dramatically at lower frequencies and barely at high frequencies. It hits around 0.5% at around 25 hz. Fortunately, humans are rather insensitive to low frequency distortion. Some studies have found even 5% THD below 100 hz is hard to detect. That’s a good thing because most transducers (speaker or headphones) tend to have rather large amounts of low frequency THD at higher volumes. So the midrange and high frequency performance here is excellent, the deepest bass is a bit disappointing but likely not an audible problem:

FiiO E5 6 db 400 mV 15 Ohms THD N Sweep Lower Traces No Load Upper 15 Ohms

NOISE: Here’s the “worst case” noise with the E5’s volume at maximum and no input. It’s 1 – 3 dB better and lower volume settings. This is acceptable noise and similar to many portable players and the Behringer UCA202. The NuForce uDAC-2 is significantly quieter.

FiiO E5 Noise Test No Input, Max Volume (ref 400 mV out)

IMD: Here’s the SMPTE IMD at 400 mV out into 15 ohms. It’s very clean:

FiiO E5 6 db 400 mV 15 Ohms IMD SMPTE

FREQUENCY RESPONSE: Here’s the frequency response with various loads. Note the divisions are only 0.5 dB. The –3 dB point is 20 hz. Or, put another way, the E5 is +/- 1.5 dB from 20 hz to 20 Khz which many would argue is “flat enough”. I would have liked to see a bit less low frequency roll off, but this isn’t bad at all as it’s only down 1.5 dB at 30 hz. Interestingly it doesn’t seem to be caused by an output capacitor because the roll off doesn’t change with loading:


FiiO E5 6db Freq 400mV No Load 25 ohm source (green) 600 ohm (yellow) 15 ohm out 25 ohm source (blue)

LOW FREQUENCY EQ OPTION (added 4/7): Below in red is the response (starting at 20 hz instead of 10 hz as above) into 150 ohms. In blue is what happens with the Bass EQ switch turned on. it’s a fairly gentle broad rise that, at its peak, is only 3 dB higher than the reference level. The peak is broadly centered around about 80 hz. Note this nicely compensates for the low frequency roll off as the response is still a bit above 0 dB even at 20 hz. As far as bass EQ goes, this is much more subtle than most. And the channel balance problem goes away with the EQ turned on.

FiiO E5 ~400 mV 150 Ohm Load Frequency Response With Bass EQ (blue)

CHANNEL SEPARATION: Here’s the channel separation and it does very well for something so tiny with the two channel jammed close together—a mostly constant 46 dB. Note this is driving a difficult 15 ohm load. The separation improves into higher impedance loads:

FiiO E5 6 db Gain 200 mV In 15 Ohms Ch Sep

1 KHZ SQUARE WAVE PERFORMANCE: The E5 also does really well here. Unlike when testing DACs with square waves, there’s no ringing from the low pass filters all DACs have. So here it shows the flat frequency response (flat top of the waveform) and stability of the amplifier (lack of much ringing):

FiiO E5 6 db Gain 15 Ohms 500 mV p-p Square Wave

10 KHZ SQUARE WAVE PERFORMANCE (added 4/7): The dScope above makes a great 24 bit high resolution oscilloscope but only up to 96 Khz. This is fine for testing digital sources (players, DACs, etc.) but to really “stress” an analog amplifier you can use a 10 KHZ signal with a very fast rise time (from a 25 Mhz Tektronix AFG3022 Waveform Generator). The signal is measured with a 100 Mhz digital oscilloscope to evaluate the “speed” and other behavior of the amplifier. The red waveform on the bottom is the input to the amplifier and the blue trace on top is the output. The rounded corners represent the high frequency roll off and the slope of the rising edge represents the rise time and slew rate. This is decent, but not high-end, performance:

FiiO E5 10 Khz 1 V p-p Square Wave (blue)

Here’s a ‘zoomed’ view of the rise time. Rise time is usually specified from the 10% to the 90% point. I didn’t use the on-screen cursors here but the time from –0.4 volts to + 0.4 volts is about 4.2 uS. The slew rate is the “flat” sloped part of the line and is about 0.4 v/uS. That sounds like a really bad number but, in practice, an amplifier only needs about 0.2 v/uS per volt of RMS output to reproduce a 20 Khz waveform perfectly. From a 44 Khz sampled digital source (i.e. CD quality audio) that’s the fastest slew rate you need. Even a 20 Khz perfect digital square wave comes out of a 44 Khz DAC as a 20 khz sine wave. So the 0.4 v/uS of the FiiO E5 means it can reproduce 20 Khz up to about 2 V RMS without slew limiting. And, because it clips around 1.4 V RMS, there’s a decent safety margin here.

FiiO E5 10 Khz 1 V p-p Rise Time Slew (blue)

TECH SUMMARY: The performance is impressive in most areas given the size and price. The extremely low 0.7 ohm output impedance and 100 mW into 16 ohm power level at low distortion are the stand outs on the good side. The bass EQ is subtle and overcomes the slight LF roll off nicely.


  1. My E5 doesn't have this problem. I used the + button to step through the entire range, and the difference in gain between the left and right channels is small, even when driving a 16-ohm load. At worst it's less than 1 dB off at the lowest settings. After about 10 steps, both channels are within 0.1dB all the way until maximum gain (5dB) which is around 63 steps higher than minimum. Unity gain is 12-13 steps lower.

    Also, I'm getting very low output impedance--0.15 ohms. The rest of the numbers look similar for my E5, except maybe channel separation. It's really a nice little amp when it works.

  2. As great reading as usual. I do have. Fiio E5 and it does not seem to have any channel imbalance issue as my iBasso t3 has at low volume thus i get you've got a lemon.

    Did you find the time to check again the output impedance of the Touch 3g. Since the iPhone 3GS has 2 Ohm the iPad 1.3 and the iPhone 4 1 ohm it looks quite stranged what you measured for the Touch

  3. For the third-generation iPod Touch, there's enough raw data on this site that you can use to estimate the output impedance, assuming that it is a simple series resistance.

    Look at the impedance measurement for the SuperFi 5 Pro:
    20 ohms at DC
    85+j0 ohms at 1200 Hz
    8+j0 ohms at 11 kHz

    Then look at the iPod's frequency response relative to 1 kHz when driving the SF5 Pro:
    -1.5 dB at 20 Hz (close enough to DC)
    0 dB at 1200 Hz
    -3.5 dB at 11 kHz (extrapolated)

    Exercise: Estimate the iPod Touch's output impedance.

    BTW, also look at the uDAC-2 headphone output's frequency response--it swings 4.5 dB with the SF5 Pro, and it's reported to have a 6-ohm output impedance. The 3rd gen iPod Touch swings only 3.5 dB.

  4. I'm afraid i that i'm utterly unable to solve the question sinceci don't have any electrical engineering background ;)

  5. I've had three or four E5, and none showed any channel imbalance.

  6. OK, I'll work on getting another E5 to double check the channel balance problem. And to Yuriv and Gonzalo, I'll double check the output impedance of the iPod Touch 3G.

  7. This is way late, but it may provide a template for determining the output impedance for other players, if a couple impedance and SPL numbers are known.

    Call the output resistance "Rsource"
    Comparing 1,200 and 11,000 hz data:
    Change in db = 20*log(V2/V1) = 3.5
    Therefore, V2/V1 = 10^(3.5/20) = 1.75

    For 1,200 hz: V2 = Vsource * (85)/(85 + Rsource)
    For 11000 hz: V1 = Vsource*(8)/(8+Rsource)
    If V2/V1 = 1.75, then:
    1.75 = (85/8)*(8 + Rsource)/(85+Rsource)
    14*(85+Rsource) = 85*(8 + Rsource)
    1190 + 14*Rsource = 680 + 85*Rsource
    510 = 71*Rsource
    Rsource = 7.183

    In the Clip+ article it was measured as 7 ohms, so this checks.

  8. It would be great if you add to your tests also distortion measurments on ~30, ~50, ~80, ~250, 300 Ohm resistive or real load.

  9. I've added 32, 80 and 600 to my newer tests see the O2 Headphone Amp for an example. More loads is more work and I'm not exactly getting paid for any of this. So lots of things would be nice, but I have to draw a reasonable line somewhere.

  10. Apparently this has been delayed from release for a while (something to do with a bundle deal with new Westone IEMs), but the FiiO E6 is supposed to be available soon. Maybe by the end of the month. I'm probably a few months late in knowing about its existence.

    E6 is very slightly smaller than the E5, at about the same price.

    Supposedly, compared to E5 (this is already secondhand info in a head-fi thread or two, so take with a grain of salt)...

    1) plastic instead of metal shell, no metal clip, but more usable (less crowded) since buttons/plugs are on more than just 2 sides

    2) two EQ choices other than flat

    3) two gain options, one of which is larger than E5's gain

    4) same op amps as E7 (? or maybe just the output amp chip), so same max power

    5) pre-amp stage now uses +- supply rails, is otherwise reworked and probably better than on E5?

    6) output impedance still < 1 ohm

    I'll believe it when I see it--or especially if one day if a sample ends up on your bench ;)--but an improvement on an already good product sounds like good news to me.

  11. I'm not clearly understnad some things so I have three questions for you. :)

    1. What is optimal input level for E5 for best perfomance?

    2. You wrote:

    "While the 650 may deserve better, even the $20 FiiO E5 can manage about 1.3 volts which might be enough for many tastes".

    "The $20 FiiO E5 can manage about 1.3 volts RMS and it got plenty loud even on highly dynamic material but the Beyer’s likely deserve better than the E5".

    "might", "likely"... What does it realy mean? :) FiiO E5 + HD650, DT770 is't bad?

    3. Can this $20 device realy improve quality of Xonar D1 + Sennheiser HD595?

    Thanks in advance. :)

  12. Alexander, it's hard to be black and white about headphone source levels. For example, people I know are about equally divided on the DT770 Pro 80 being "iPod compatible". The iPod clips on the top few settings of its volume control with typical recordings. So if you try to play it at full volume it distorts the sound. And if you turn it down a few notches so it's not clipping, it's not loud enough for some tastes with the Beyers. It's personal preference.

    The same is true with the E5 and similar headphones where it's a marginal match for power requirements. It really depends on the type of music and how loud someone wants to listen. Highly dynamic music, like classical or well recorded jazz, is much more likely to be a problem than heavily compressed pop music.

    The E5 can improve the sound of even some really expensive gear because many have at least a 10 ohm output impedance. Please see my article on Headphone & Amp Impedance for more. The rule of thumb is the headphones have to be at least 8 times the amp's output impedance. So for the Xonar D1 (which if it's like other Xonar gear has a 10 ohm output impedance) that means 80 ohm or higher headphones.

    If you have 32 ohm Grados, or 25 ohm Denons, etc., the E5 will absolutely improve the output of the Xonar by lowering the output impedance.

    Any input up from 0.5 to 1.2 V RMS works fine which includes the output from nearly all portable players. The 2+ V line outputs of home gear, however, is a serious problem.

  13. Thank you for answer!

    Xonar D1 have 50 Ohm ouput impedance.

    How can I detect what input is higher than needed? THD on specific frequencies? I can measure some things with RMAA. On what I need to pay attention?

  14. RMAA has no concept of absolute levels (everything is just relative to whatever 0 dBFS is for your soundcard/devices inputs). So the best you can do is play RMAA test files into the E5 from various sources at various levels, keeping the volume on the E5 set as low as possible, and look for high distortion levels in the RMAA results. But you're really working "in the dark". See my RMAA article for tips on how to get the most out of RMAA.

    The E5 wasn't designed for use with home gear. It's designed for portable use. If you want something to lower the extremely high output impedance of the D1 I would suggest waiting until someone sells either an assembled O2 Headphone Amp or at least pre-assembled circuit boards. I'm pretty sure you won't find a better amp for less and it can handle any input level you're likely to ever encounter.

  15. O2 is VERY intresting amp but I doubt I can get it even in future for reasonable price as assembled device. If our chinese friends will make and sell it for reasonable price then I surely buy it. But I doubt that this happen.

  16. Would be nice if there was a meter, clipping, or input level light, assuming the input level is a problem if you go too much over 1V.

  17. Do you know how work volume control on E5? As I understand from tpa6130 datasheet it's attenuate signal by changing input impedance. It seems not worse than standart potentiometer volume control. What you think about this?

  18. The volume works great on the E5 (and E7 with the same chip). It is very accurate, has small step sizes, and apparently measures fairly well.

  19. If there's any chance to review the E6 it'd be great. First RMAA (Yes i know;) shows that the bass roll off has been fixed. This alone would make it the best bang for the buck portable amp for driving balanced armatures.

  20. Well this is all very interesting especially considering I've had the E5 dismissed as totally inadequate for driving my power hungry orthos, the Fostex T50rp's. I've been looking at getting a vintage Rotel integrated amplifier to do the job. However, it's clear that the issue isn't quite so simply as you mention that the E5 may not be enough for some phones. Do you think the E5 could drive these orthos? They are rated at 50ohms, sensitivity of 98dB and max power of 3000mW (if that means anything in this context).

    I might just have to try building the O2.

  21. There's already an O2 owner with Fostex T50 cans who's happy. But no, the E5 doesn't have enough output. Not even close. Neither does any other amp FiiO makes except the E9 but its 10 ohm output impedance is less than ideal.

  22. Great, thanks for that, NwAvGuy! I am rather hoping to have a justification for this project. I've read elsewhere on your eye-poppingly enjoyable blog some of your writings giving the impression (now that I can't find the original source) that most would be better off with a decent headphone amp, ie. not running off an old integrated amplifier. I think it was related to high output impedance. But would that also be true of orthos? I got the impression elsewhere that orthos can do mighty fine with integrated amps, even despite impedance mismatches, assuming that they are running directly off the amp (via resistors) and not through an opamp. Any opinion on that?

  23. @GregL, I'm not sure about your Fostex, but in general ortho (planar) headphones have a relatively flat impedance curve. As long as that's true, they should work reasonably OK with an integrated amp or receiver.

  24. Ok, thanks for that. In that case I think I may put off the O2 until more UK group buys come along.

  25. Great review as usual, I know I'm kinda late to the party, but my Fostex T20RP presented tough challenge (50 ohms/96dB SPL/mW) for UCA202. With added E5 I get better levels without clipping or distortion - much better sound all and all.
    I payed $19 for my Fiio E5 of Amazon

  26. Thanks for the very detailed information about the FiiO E5. I bought it through amazon and it's a great thing spent for $19. I never had any technical problems. I used a Heat Shrink to attach it to a stereo and it's perfect!


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