tomscy2000
Headphoneus Supremus
In recent months, as part of FiiO's internal testing programme, I've been privileged to test out revisions to FiiO's well-received E10 and E11 products, the E10K and E11K, respectively.
The E10K and E11K, despite being named 'K' revisions of the original models and thus might connote minor changes, are significantly reworked over their predecessors. The E10K, despite sharing the basic overall chassis of the E10, sports an all-new DAC chip and analog output stage --- little from the old E10 is recycled. The E11K additionally wears new clothes and has an analog topology that has been significantly redone over the original E11. It is not change for the the sake of it, either --- these changes are unquestionably for the better, in both measured performance and subjective enjoyment.
The following are my notes for the E10K and E11K; they are direct, dry, and to the point --- in some ways academic.
Figure 1 -- FiiO E10K, 3/4 view.
FiiO representative [b]JoeBloggs[/b] announced the arrival of the E10K in this thread.
With the exception of the switches used, the E10K is largely unchanged in appearance (Fig. 1). The biggest change is the move of the gain switch from the bottom of the unit to the back, a welcome ergonomic improvement. The large metal switches have been changed out for smaller plastic ones, but according to FiiO, these switches are actually more robust, are rated for a higher number of toggles, and have lower failure rates.
Figure 2 -- Top Side, E10K PCB (Beta/Pre-Production, Q1 2014)
Figure 3 -- Bottom Side, E10K PCB (Beta/Pre-Production, Q1 2014)
The E10K preserves the Galaxy Far-East Company TENOR TE7022L USB receiver --- one of the few parts carried over from the E10 of old (the E07K, E17, and E18 all also use this part, in addition to many other devices from other brands, such as the JDS Labs ODAC).
As such, the E10K remains an isochronous USB device. Upon inspection of the PCB board, I discovered a ROM part (see Fig. 2) that most likely serves as an elastic digital layer buffer for I/O. In that sense, the USB transfer protocol is likely more of an "adaptive" variant of isochronous transfer. The TE7022L uses a 12 MHz oscillator to generate its transport clock; the XO can be found in the top right-hand corner of the TE7022L in Fig. 3.
The E10K is an USB Audio Class 1.0 (UAC1) device, and thus only supports up to 96 kHz sample rates. To support sample rates beyond 96 kHz, FiiO would have to use an USB Audio Class 2.0 part (e.g. XMOS, C-Media CM6631A) and thus necessitate installation of device drivers in the Windows environment (OSX natively supports UAC2).
The largest drawback of the TE7022L is its lack of support for 88.2 kS/s sample rates. It's difficult to fathom why it's so, but if you intend on playing 24/88.2 music with the E10K, you'll have to perform a downsample with a decimation factor of two, from 88.2 to 44.1 kS/s, using a plugin such as SoX resampler.
I asked FiiO about the possibility of switching to an asynchronous USB receiver part, such as the affordable Bravo SA9027 from SaviTech (used in products like the JDS Labs C5D, Stoner Acoustics UD110, and HiFiMeDIY U2 Sabre DAC), but FiiO stated that they'd tested the SA9027 and decided the TE7022L was still a more stable, mature part. With their long-standing experience with the TENOR, and multiple product offerings that use the part (i.e. lots of ready stock, lower bulk prices), it makes sense that FiiO wanted to stick with the TENOR part. If well-implemented, in an ideal situation and board layout, I've heard that the TE7022L can get down to the order of a couple hundred picoseconds of jitter --- not world-class, but certainly not bad at all.
It also possesses built-in S/PDIF transceiver capabilities, making for extra functionality that carries over from the original E10, allowing for a penalty-free preservation of the coaxial output in the device.
There is the possibility that the E10K might work with Android devices over OTG, but I have neither confirmed this functionality with FiiO, nor have I tested it myself.
The DAC chip has been changed, from the often-used and venerable Wolfson WM8740 to the TI/Burr-Brown PCM5102A.
The PCM5102, like the WM8740, is a voltage output DAC chip. However, since it has a charge pump integrated into the IC, the PCM5102 is capable of delivering a true, Red Book friendly, ground-referenced 2 Vrms at the output. As such, the design methodology centered around this chip solution is less complex than with other DAC designs, simplifying both PCB layout and the number of components necessary. The built-in PLL mode of the PCM5102A also allows the E10K to function without a master clock oscillator or a clock generator (e.g. PLL1707), further simplifying digital design by accepting just a three-wire I2S input from the TE7022L. The simplified design also reduces possible EMI. Using a discrete clock design probably just complicates design a lot more and balloons the BOM cost. Thus, these parts choices inform us of the following: one of the design goals of the E10K was to improve performance without raising costs (if not outright cutting costs). Switching to this design helps get FiiO to that goal.
During the development process, I requested that FiiO look into implementation of the low-latency IIR minimum phase interpolation filter built into the PCM5102; both the Meridian Explorer and the JDS Labs C5D have the filter enabled. In the end, FiiO chose not to enable the filter, opting for the normal FIR linear phase filter. While pre-ringing is not eliminated, there are no phase distortions introduced.
Set at 0.55fs, the low-latency filter would have also introduced additional aliasing images, suppressed by about -40 dB, and thus aliasing would perhaps be audible at very high frequencies. Oversampling in PLL mode is conducted at a lower system rate, so the E10K wouldn't have the luxury of using shallower reconstruction filters.
This section is all-new for the E10K. The current buffer, as mentioned in marketing materials, is the LMH6643, a voltage-feedback opamp capable of delivering 75 mA current, and is employed in both the E18 and the X5. Full scale output is referenced to 2.6 Vrms, which equates to roughly 200 mW into 32 ohms.
There's an LM2663 switching power regulator that serves to double/invert the power supply to meet different power needs across the board.
There is a gain stage to the E10K, which is responsible for switching between the +1/+9 dB gain selection, the duties of which are performed by the OPA1642,located right behind the ALPS potentiometer and surrounded by a bevy of resistors (different groups of resistors for feedback for different gain?). The volume pot is rated for <0.4 dB of tracking differential.
There is also an unknown opamp located right next to the LMH6643 in the middle of the board; at first I thought it was the OPA1642, but it was not the case. The printing is too faint to decipher. It is a TI part (FiiO uses TI heavily) in an SOIC package, but I cannot decipher anything else beyond that (see Fig. 2). It's possible it's used in the bass boost feedback loop, but I cannot say for sure. While I've improved my knowledge in audio design, I can only say I'm a mere dilettante and not a learned EE.
Residual noise of the E10K's line output is at a healthy <10 uV RMS, while the headphone output is <15 uV RMS. That's admirable performance for an USB-powered DAC at the ~$100 price point. Take, for example, the HRT MicroStreamer, a well-received USB DAC that competes at a similar (but higher) price point to the E10K and has 18 uV RMS. Those little linear regulators that you see littered across the E10K's PCB board, while not boutique parts, are definitely doing their job.
The E10 of old had an issue of lots of noise rustling through when plugging/unplugging headphones (too much DC bleeding through?). That issue has been resolved in the E10K. While plugging in headphones isn't a completely silent affair, it is quiet enough not to be a bother for anyone.
Overall, I find the the FiiO E10K to be a very competent unit and generally a very good improvement over its predecessor. The E10 was a warm, intimate unit that sounded pleasant but rolled off on its ends. The successor E10K is a far more neutral-sounding device with little roll-off and more detailing, though it does still generally hint at warmth.
Presentation-wise, the soundstage and center image are cast somewhat intimately, but not quite forward. Overall, it feels laid-back. The E11K sounds more spacious a bit brighter (more later).
Bass boost this time around is more subtle than it was in the E10, aimed at bringing presence to music, rather than boosting the "boom" of added mid-bass response. Thus, the effect is somewhat subtle but still present.
A/B-ing between the E10K and the Resonessence Labs Concero HP, the E10K decidedly lost the competition (and with good reason --- the Concero HP costs more than eight times that of the E10K). The primary goal wasn't whether the E10K could acquit itself; it was to subjectively measure the E10K against a well-implemented jitter rejection paradigm of the Concero HP, a DAC that employs low-latency asynchronous USB transfer, discrete clocks for 44.1/48 kHz multiples, additional FPGA sub-routines for jitter timing, and ESSTech's built-in asynchronous sample rate converter. The E10K sounded a bit splashy compared to the Concero HP in the high frequencies. I tried testing some "jitter-sensitive" tracks, such as the evolution of the sound of the shakers in Rebecca Pidgeon's 'Spanish Harlem', and I did find the E10K to be a bit more indistinct with less dimensional movement across the soundstage, but if you weren't specifically looking for problems, I doubt anyone would even notice. I also found subjective jitter performance to be a little better on the AudioQuest Dragonfly 1.2, but the Dragonfly sounded a little boring to me overall.
The E10K performed well with low-impedance, full-sized headphones such as the NAD Viso HP50 and the Focal Spirit Classic. Neither headphone is exactly "hard-to-drive", however.
With IEMs, aside from the smaller center image cast, I found the relaxed, very slightly warm presentation of the E10K ideal for my collection of earphones, ranging from the UERM to the Noble 4C. Never did I ever feel the E10K was somehow "slow", "lacking weight", or anything like that.
The majority of these notes will center around design, usability, and subjective sound performance.
Figure 4 -- Top side of the FiiO E11K.
Figure 5 -- FiiO E11K placed upright, viewed from the top.
The exterior is significantly improved over the E11. Not only does it look sharp and sleek (it takes a little after the shape of a liquor flask), it sports a brushed metal body that looks and feels premium. The body feels like one-piece aluminum (with the exception of the front and back plates) and does not bend or flex at all.
Styling stays in line with the FiiO minimalistic look, but adds an added dimension of a curved surface that I feel enhances the sleekness of the entire unit (see Figs. 4 & 5). Contrast this look to the boxy, plasticky E11 of old, and it's obvious that the E11K is a huge step up in the looks and durability department.
Size and dimensions are about the same size as an Astell&Kern AK100. One could probably use the E11K in conjunction with the now affordable AK100 and get a very nice quality portable rig that manages to still look great.
Keep in mind, however, that the metal chassis balloons the weight of the E11K to 92 g, up from the 65 g of the E11.
Since the exterior fascia of the E11K is now a much sleeker looking entity, it does now lose the ability to change batteries.
The E11K has one huge step up in functionality over the E11: playback during recharging.
The inability of the E11 to operate during playback was one of the most oft-cited complaints in E11 reviews; FiiO has responded in kind by adding that functionality.
To conform to EU standards, charging is now performed via micro-USB, located at the center of the bottom plate. Battery life is pretty good; I'm able to use the E11K across multiple sessions (each several hours each) without needing to recharge. The manual of the E11K states that battery life is ~18 hours per charge.
When the battery is low, the E11K will shut down automatically and the blue LED (located immediately to the right of the micro USB port, in Fig. 6) will blink slowly. It was good to know, because I've used the E11K to depletion a couple of times and would wonder why my music suddenly turned off, only to find the blue blinking light in the back.
Figure 6 -- Bottom plate of the E11K.
Figure 7 -- Top plate of the E11K.
Interestingly, the inputs and outputs of the E11K are located at the "bottom" of the unit, while the volume pot, gain switches, and bass boost toggle are at the "top".
While the exterior of the unit looks great, real world usage of the E11K feels slightly awkward because of the placement of the 3.5 mm sockets, and the convex curvature of the body.
Most people prefer to plug in their headphones and directly start adjusting the volume and other controls, so it feels a little strange to have to plug your headphones into the bottom of the unit and then move to the top before being able to adjust gain/bass/volume. Once you get used to it, the change in the locations of controls is not so bad, but it takes some time.
While I personally don't feel too inconvenienced, there definitely will be people who won't get along well with the E11K's curved body, as it does tend to spin atop a smooth surface and would be difficult to strap securely to a DAP such as the AK100. A simple fix would be to place a piece of anti-slip grip sheet between the E11K and the DAP, so perhaps it'd be a good idea if FiiO included a small square of that material with every E11K, as well as tension bands.
My complaint: upon start-up, if you have your headphones plugged into the unit already, the E11K will produce a very large "pop" sound that is especially loud on sensitive multi-BA IEMs. FiiO has informed me that they've been actively working on suppressing the pop as much as possible for the final retail version, so keep in mind that this loud "pop" sound in question is found in the beta engineering unit that I have, and may not necessarily be that loud in the final retail version. However, I would still recommend that people turn on the amplifier before plugging in headphones just to be safe. Even with full-sized headphones such as the NAD Viso HP50 and Focal Spirit Professional, the "pop" sound was somewhat loud.
Tracking on the volume pot is good; Low volume imbalance disappears between the "2" to "3" mark. Because I'm generally a guy who does very fine adjustments to volume, I quite appreciate the Astell&Kern style volume pot guards.
For IEM users, low gain (+0 dB, 1x) is acceptable for fine control of volume for low-voltage output devices such as smartphones (e.g. iPhone) and low-power DAPs (e.g. Astell&Kern AK100). I paired the E11K with the Sony NWZ-F886, which has a maximum output of 1.25 Vrms, and most music was more than loud enough at the "3" to "4" mark when listening through the UERM. However, be wary of volumes when playing music from full 2 Vrms line output devices. Music volumes will be plenty loud between "2" and "3".
At high gain (+10 dB), the E11K is quite loud; coupled with its 250 mW output power into 32 ohms, the amplifier drove the NAD Viso HP50 with authority to volumes way beyond what I'm used to. I'm sure it could drive most moderate headphones on the market with ease.
Bass boost is now single stage rather than dual stage in the E11. Personally, I don't mind the omission if it means a good single stage bump in bass presence. Implementation feels similar to that of the E10K in sound.
The addition of the charge-and-play function also means that the E11K is no longer the three-channel, virtual ground design employed in the E11. However, it does still manage to use the AD8397, which is one of the most powerful opamps around, delivering both rail-to-rail output and high current. I've always been a fan of the AD8397 (if implemented properly) and the E11K feels right to me. In terms of numbers, both power and distortion are improved in this iteration.
For the price range, the E11 has always been a decent product. The E11K should be even better. In the past, I found the E11 a little "hot" in the treble, leading to some roughness and exaggerated sibilant tones. While the E11K retains some of these characteristics, the tone is mostly neutral and the roughness of the E11 is definitely improved upon.
It's tough to say which unit preserves resolution from its input best because the rough edginess of the E11 tends to overemphasize certain things and keep me from accurately assessing the quality of the reproduced music, but I do clearly sense a greater depth to the presentation in the E11K, perhaps suggestive of greater transparency in the revised design. Width of presentation is about the same.
While I haven't performed any load tests, I doubt most headphone loads will sag, so the sound should be pretty even with a lot of different headphones, even with very reactive loads --- one of the advantages of having a high current, rail-to-rail opamp like the AD8397.
Bass boost on the E11K is voiced similarly to bass boost on the E10K, more subtle than obvious. In general, I'm not a person who uses bass boost, but few people should be disappointed by the bass boost in the E11K.
Compared to the slightly warmer E10K, the E11K possesses a more open presentation; everything feels just a bit more spacious, and thus I enjoy pairing the E11K with the E10K's line output for budget 1-2 punch.
Overall, you won't get the warm refinement of tone like you'd get from something like the JDS Labs C5 (which itself outclasses pricier offerings), but the overall sound of the E11K is quite nice and will service most people quite well. I could easily live with the sound of the E11K and not feel the need to buy into the C5.
The improvements are clear; not only are measurements improved across the board, but subjective perceptions have gotten better as well. The introduction of the E10K and E11K is the culmination of FiiO's maturing know-how and I feel they've done a great job with these two products and sound-wise, they're once again punching above their weight class, whilst preserving the company's mission to bring affordable yet high-quality audio to the masses.
They're not perfect, of course, and if you're able to stretch your budget by $100-150, you can find alternatives to both units that are also very excellent and further take technology to a different level, such as the JDS Labs C5/C5D or LH Labs Geek Out 100/450/720/1000. However, if your budget is restricted, there's pretty much nothing better. FiiO improves on their ruggedized exterior designs and have added admirable audio performance to boot. Few people would be disappointed by either the E10K or the E11K.
Keep in mind that these notes were written for the evaluation of pre-release, beta engineering units of both the E10K and E11K. Final production units will likely show greater reliability and performance.
The E10K and E11K, despite being named 'K' revisions of the original models and thus might connote minor changes, are significantly reworked over their predecessors. The E10K, despite sharing the basic overall chassis of the E10, sports an all-new DAC chip and analog output stage --- little from the old E10 is recycled. The E11K additionally wears new clothes and has an analog topology that has been significantly redone over the original E11. It is not change for the the sake of it, either --- these changes are unquestionably for the better, in both measured performance and subjective enjoyment.
The following are my notes for the E10K and E11K; they are direct, dry, and to the point --- in some ways academic.
E10K
Figure 1 -- FiiO E10K, 3/4 view.
FiiO representative [b]JoeBloggs[/b] announced the arrival of the E10K in this thread.
Exterior/Features
With the exception of the switches used, the E10K is largely unchanged in appearance (Fig. 1). The biggest change is the move of the gain switch from the bottom of the unit to the back, a welcome ergonomic improvement. The large metal switches have been changed out for smaller plastic ones, but according to FiiO, these switches are actually more robust, are rated for a higher number of toggles, and have lower failure rates.
Technical Details
Figure 2 -- Top Side, E10K PCB (Beta/Pre-Production, Q1 2014)
Figure 3 -- Bottom Side, E10K PCB (Beta/Pre-Production, Q1 2014)
USB Receiver and S/PDIF Conversion
The E10K preserves the Galaxy Far-East Company TENOR TE7022L USB receiver --- one of the few parts carried over from the E10 of old (the E07K, E17, and E18 all also use this part, in addition to many other devices from other brands, such as the JDS Labs ODAC).
As such, the E10K remains an isochronous USB device. Upon inspection of the PCB board, I discovered a ROM part (see Fig. 2) that most likely serves as an elastic digital layer buffer for I/O. In that sense, the USB transfer protocol is likely more of an "adaptive" variant of isochronous transfer. The TE7022L uses a 12 MHz oscillator to generate its transport clock; the XO can be found in the top right-hand corner of the TE7022L in Fig. 3.
The E10K is an USB Audio Class 1.0 (UAC1) device, and thus only supports up to 96 kHz sample rates. To support sample rates beyond 96 kHz, FiiO would have to use an USB Audio Class 2.0 part (e.g. XMOS, C-Media CM6631A) and thus necessitate installation of device drivers in the Windows environment (OSX natively supports UAC2).
The largest drawback of the TE7022L is its lack of support for 88.2 kS/s sample rates. It's difficult to fathom why it's so, but if you intend on playing 24/88.2 music with the E10K, you'll have to perform a downsample with a decimation factor of two, from 88.2 to 44.1 kS/s, using a plugin such as SoX resampler.
I asked FiiO about the possibility of switching to an asynchronous USB receiver part, such as the affordable Bravo SA9027 from SaviTech (used in products like the JDS Labs C5D, Stoner Acoustics UD110, and HiFiMeDIY U2 Sabre DAC), but FiiO stated that they'd tested the SA9027 and decided the TE7022L was still a more stable, mature part. With their long-standing experience with the TENOR, and multiple product offerings that use the part (i.e. lots of ready stock, lower bulk prices), it makes sense that FiiO wanted to stick with the TENOR part. If well-implemented, in an ideal situation and board layout, I've heard that the TE7022L can get down to the order of a couple hundred picoseconds of jitter --- not world-class, but certainly not bad at all.
It also possesses built-in S/PDIF transceiver capabilities, making for extra functionality that carries over from the original E10, allowing for a penalty-free preservation of the coaxial output in the device.
There is the possibility that the E10K might work with Android devices over OTG, but I have neither confirmed this functionality with FiiO, nor have I tested it myself.
Digital-to-Analogue Converter
The DAC chip has been changed, from the often-used and venerable Wolfson WM8740 to the TI/Burr-Brown PCM5102A.
The PCM5102, like the WM8740, is a voltage output DAC chip. However, since it has a charge pump integrated into the IC, the PCM5102 is capable of delivering a true, Red Book friendly, ground-referenced 2 Vrms at the output. As such, the design methodology centered around this chip solution is less complex than with other DAC designs, simplifying both PCB layout and the number of components necessary. The built-in PLL mode of the PCM5102A also allows the E10K to function without a master clock oscillator or a clock generator (e.g. PLL1707), further simplifying digital design by accepting just a three-wire I2S input from the TE7022L. The simplified design also reduces possible EMI. Using a discrete clock design probably just complicates design a lot more and balloons the BOM cost. Thus, these parts choices inform us of the following: one of the design goals of the E10K was to improve performance without raising costs (if not outright cutting costs). Switching to this design helps get FiiO to that goal.
During the development process, I requested that FiiO look into implementation of the low-latency IIR minimum phase interpolation filter built into the PCM5102; both the Meridian Explorer and the JDS Labs C5D have the filter enabled. In the end, FiiO chose not to enable the filter, opting for the normal FIR linear phase filter. While pre-ringing is not eliminated, there are no phase distortions introduced.
Set at 0.55fs, the low-latency filter would have also introduced additional aliasing images, suppressed by about -40 dB, and thus aliasing would perhaps be audible at very high frequencies. Oversampling in PLL mode is conducted at a lower system rate, so the E10K wouldn't have the luxury of using shallower reconstruction filters.
Analogue Design
This section is all-new for the E10K. The current buffer, as mentioned in marketing materials, is the LMH6643, a voltage-feedback opamp capable of delivering 75 mA current, and is employed in both the E18 and the X5. Full scale output is referenced to 2.6 Vrms, which equates to roughly 200 mW into 32 ohms.
There's an LM2663 switching power regulator that serves to double/invert the power supply to meet different power needs across the board.
There is a gain stage to the E10K, which is responsible for switching between the +1/+9 dB gain selection, the duties of which are performed by the OPA1642,
Noise/Hum
Residual noise of the E10K's line output is at a healthy <10 uV RMS, while the headphone output is <15 uV RMS. That's admirable performance for an USB-powered DAC at the ~$100 price point. Take, for example, the HRT MicroStreamer, a well-received USB DAC that competes at a similar (but higher) price point to the E10K and has 18 uV RMS. Those little linear regulators that you see littered across the E10K's PCB board, while not boutique parts, are definitely doing their job.
The E10 of old had an issue of lots of noise rustling through when plugging/unplugging headphones (too much DC bleeding through?). That issue has been resolved in the E10K. While plugging in headphones isn't a completely silent affair, it is quiet enough not to be a bother for anyone.
Sound
Overall, I find the the FiiO E10K to be a very competent unit and generally a very good improvement over its predecessor. The E10 was a warm, intimate unit that sounded pleasant but rolled off on its ends. The successor E10K is a far more neutral-sounding device with little roll-off and more detailing, though it does still generally hint at warmth.
Presentation-wise, the soundstage and center image are cast somewhat intimately, but not quite forward. Overall, it feels laid-back. The E11K sounds more spacious a bit brighter (more later).
Bass boost this time around is more subtle than it was in the E10, aimed at bringing presence to music, rather than boosting the "boom" of added mid-bass response. Thus, the effect is somewhat subtle but still present.
A/B-ing between the E10K and the Resonessence Labs Concero HP, the E10K decidedly lost the competition (and with good reason --- the Concero HP costs more than eight times that of the E10K). The primary goal wasn't whether the E10K could acquit itself; it was to subjectively measure the E10K against a well-implemented jitter rejection paradigm of the Concero HP, a DAC that employs low-latency asynchronous USB transfer, discrete clocks for 44.1/48 kHz multiples, additional FPGA sub-routines for jitter timing, and ESSTech's built-in asynchronous sample rate converter. The E10K sounded a bit splashy compared to the Concero HP in the high frequencies. I tried testing some "jitter-sensitive" tracks, such as the evolution of the sound of the shakers in Rebecca Pidgeon's 'Spanish Harlem', and I did find the E10K to be a bit more indistinct with less dimensional movement across the soundstage, but if you weren't specifically looking for problems, I doubt anyone would even notice. I also found subjective jitter performance to be a little better on the AudioQuest Dragonfly 1.2, but the Dragonfly sounded a little boring to me overall.
The E10K performed well with low-impedance, full-sized headphones such as the NAD Viso HP50 and the Focal Spirit Classic. Neither headphone is exactly "hard-to-drive", however.
With IEMs, aside from the smaller center image cast, I found the relaxed, very slightly warm presentation of the E10K ideal for my collection of earphones, ranging from the UERM to the Noble 4C. Never did I ever feel the E10K was somehow "slow", "lacking weight", or anything like that.
E11K
I was asked to evaluate the E11K as an end-user, so I'm much more fuzzy about the technical details of the E11K than I am about the E10K.The majority of these notes will center around design, usability, and subjective sound performance.
Figure 4 -- Top side of the FiiO E11K.
Figure 5 -- FiiO E11K placed upright, viewed from the top.
Exterior/Aesthetics
The exterior is significantly improved over the E11. Not only does it look sharp and sleek (it takes a little after the shape of a liquor flask), it sports a brushed metal body that looks and feels premium. The body feels like one-piece aluminum (with the exception of the front and back plates) and does not bend or flex at all.
Styling stays in line with the FiiO minimalistic look, but adds an added dimension of a curved surface that I feel enhances the sleekness of the entire unit (see Figs. 4 & 5). Contrast this look to the boxy, plasticky E11 of old, and it's obvious that the E11K is a huge step up in the looks and durability department.
Size and dimensions are about the same size as an Astell&Kern AK100. One could probably use the E11K in conjunction with the now affordable AK100 and get a very nice quality portable rig that manages to still look great.
Keep in mind, however, that the metal chassis balloons the weight of the E11K to 92 g, up from the 65 g of the E11.
Features/Usability
Since the exterior fascia of the E11K is now a much sleeker looking entity, it does now lose the ability to change batteries.
The E11K has one huge step up in functionality over the E11: playback during recharging.
The inability of the E11 to operate during playback was one of the most oft-cited complaints in E11 reviews; FiiO has responded in kind by adding that functionality.
To conform to EU standards, charging is now performed via micro-USB, located at the center of the bottom plate. Battery life is pretty good; I'm able to use the E11K across multiple sessions (each several hours each) without needing to recharge. The manual of the E11K states that battery life is ~18 hours per charge.
When the battery is low, the E11K will shut down automatically and the blue LED (located immediately to the right of the micro USB port, in Fig. 6) will blink slowly. It was good to know, because I've used the E11K to depletion a couple of times and would wonder why my music suddenly turned off, only to find the blue blinking light in the back.
Figure 6 -- Bottom plate of the E11K.
Figure 7 -- Top plate of the E11K.
Interestingly, the inputs and outputs of the E11K are located at the "bottom" of the unit, while the volume pot, gain switches, and bass boost toggle are at the "top".
While the exterior of the unit looks great, real world usage of the E11K feels slightly awkward because of the placement of the 3.5 mm sockets, and the convex curvature of the body.
Most people prefer to plug in their headphones and directly start adjusting the volume and other controls, so it feels a little strange to have to plug your headphones into the bottom of the unit and then move to the top before being able to adjust gain/bass/volume. Once you get used to it, the change in the locations of controls is not so bad, but it takes some time.
While I personally don't feel too inconvenienced, there definitely will be people who won't get along well with the E11K's curved body, as it does tend to spin atop a smooth surface and would be difficult to strap securely to a DAP such as the AK100. A simple fix would be to place a piece of anti-slip grip sheet between the E11K and the DAP, so perhaps it'd be a good idea if FiiO included a small square of that material with every E11K, as well as tension bands.
My complaint: upon start-up, if you have your headphones plugged into the unit already, the E11K will produce a very large "pop" sound that is especially loud on sensitive multi-BA IEMs. FiiO has informed me that they've been actively working on suppressing the pop as much as possible for the final retail version, so keep in mind that this loud "pop" sound in question is found in the beta engineering unit that I have, and may not necessarily be that loud in the final retail version. However, I would still recommend that people turn on the amplifier before plugging in headphones just to be safe. Even with full-sized headphones such as the NAD Viso HP50 and Focal Spirit Professional, the "pop" sound was somewhat loud.
Tracking on the volume pot is good; Low volume imbalance disappears between the "2" to "3" mark. Because I'm generally a guy who does very fine adjustments to volume, I quite appreciate the Astell&Kern style volume pot guards.
For IEM users, low gain (+0 dB, 1x) is acceptable for fine control of volume for low-voltage output devices such as smartphones (e.g. iPhone) and low-power DAPs (e.g. Astell&Kern AK100). I paired the E11K with the Sony NWZ-F886, which has a maximum output of 1.25 Vrms, and most music was more than loud enough at the "3" to "4" mark when listening through the UERM. However, be wary of volumes when playing music from full 2 Vrms line output devices. Music volumes will be plenty loud between "2" and "3".
At high gain (+10 dB), the E11K is quite loud; coupled with its 250 mW output power into 32 ohms, the amplifier drove the NAD Viso HP50 with authority to volumes way beyond what I'm used to. I'm sure it could drive most moderate headphones on the market with ease.
Bass boost is now single stage rather than dual stage in the E11. Personally, I don't mind the omission if it means a good single stage bump in bass presence. Implementation feels similar to that of the E10K in sound.
Analog Design Topology
The addition of the charge-and-play function also means that the E11K is no longer the three-channel, virtual ground design employed in the E11. However, it does still manage to use the AD8397, which is one of the most powerful opamps around, delivering both rail-to-rail output and high current. I've always been a fan of the AD8397 (if implemented properly) and the E11K feels right to me. In terms of numbers, both power and distortion are improved in this iteration.
Sound
For the price range, the E11 has always been a decent product. The E11K should be even better. In the past, I found the E11 a little "hot" in the treble, leading to some roughness and exaggerated sibilant tones. While the E11K retains some of these characteristics, the tone is mostly neutral and the roughness of the E11 is definitely improved upon.
It's tough to say which unit preserves resolution from its input best because the rough edginess of the E11 tends to overemphasize certain things and keep me from accurately assessing the quality of the reproduced music, but I do clearly sense a greater depth to the presentation in the E11K, perhaps suggestive of greater transparency in the revised design. Width of presentation is about the same.
While I haven't performed any load tests, I doubt most headphone loads will sag, so the sound should be pretty even with a lot of different headphones, even with very reactive loads --- one of the advantages of having a high current, rail-to-rail opamp like the AD8397.
Bass boost on the E11K is voiced similarly to bass boost on the E10K, more subtle than obvious. In general, I'm not a person who uses bass boost, but few people should be disappointed by the bass boost in the E11K.
Compared to the slightly warmer E10K, the E11K possesses a more open presentation; everything feels just a bit more spacious, and thus I enjoy pairing the E11K with the E10K's line output for budget 1-2 punch.
Overall, you won't get the warm refinement of tone like you'd get from something like the JDS Labs C5 (which itself outclasses pricier offerings), but the overall sound of the E11K is quite nice and will service most people quite well. I could easily live with the sound of the E11K and not feel the need to buy into the C5.
Concluding, Integrative Thoughts
Over the past year, FiiO has pushed out some excellent products. The company's X5 portable player is an immense performer at less than $400, and the entire FiiO portfolio is evolving and getting better with each release.The improvements are clear; not only are measurements improved across the board, but subjective perceptions have gotten better as well. The introduction of the E10K and E11K is the culmination of FiiO's maturing know-how and I feel they've done a great job with these two products and sound-wise, they're once again punching above their weight class, whilst preserving the company's mission to bring affordable yet high-quality audio to the masses.
They're not perfect, of course, and if you're able to stretch your budget by $100-150, you can find alternatives to both units that are also very excellent and further take technology to a different level, such as the JDS Labs C5/C5D or LH Labs Geek Out 100/450/720/1000. However, if your budget is restricted, there's pretty much nothing better. FiiO improves on their ruggedized exterior designs and have added admirable audio performance to boot. Few people would be disappointed by either the E10K or the E11K.
Keep in mind that these notes were written for the evaluation of pre-release, beta engineering units of both the E10K and E11K. Final production units will likely show greater reliability and performance.
