INTRO: I reviewed the amazingly small and inexpensive FiiO E5 back in this blog’s infancy. I was fairly impressed with the build quality and even found the audio performance acceptable considering the $20 price. But it did have some significant flaws. FiiO saw fit to release a supposedly improved successor to the E5 and named it, appropriately, the E6. It’s also interesting to see how it compares to my recent review of the $65 FiiO E11.
THE FiiO E6: The street price has gone from $20 for the E5 up to $25 – $30 for the FiiO E6. FiiO unfortunately ditched the dedicated EQ switch and has combined that function with the power switch. The good news is the controls are now easier to use without looking at the amplifier with the multi-function switch and volume control on opposite sides. It comes with a USB charging cable and a short 3.5mm male to 3.5mm male audio cable to connect to a portable player, etc. Like the E5, the E6 uses a very common mini-USB connector for charging so if you lose the cable you probably have another one lying around. Just to be clear, the mini USB port is only for charging--the E6 is not a DAC. Unlike the E11, you can use the E6 while it’s charging.
GOING BACKWARDS: For the extra 25% – 50% FiiO removes from your bank account (compared to the E5) you get an easily scratched shiny black plastic enclosure instead of the sexy satin finished metal one on the E5. The solid spring loaded metal clip on the back of the E5 has been replaced with a removable clear plastic clip seen flanking the amp in the photo above (click for a larger view). Both of these appear to be cost saving measures and a step backwards in build quality. It’s sad to see a company substantially raise the price and give you less. But the cheaper case and clip may not matter much to some—especially those who don’t want a clip.
SIX IN ONE SWITCH: The sliding spring loaded power switch (which also has a “lock” position) provides six functions in the E6: On, Off, EQ OFF, EQ1, EQ2, and 2 volt mode, There are two levels of bass EQ versus the single EQ option on the E5. There’s also a new mode to allow 2 Vrms of input without overloading the amp. These three options are indicated by a tiny LED on the back that glows red, blue, or purple depending on how many times you momentarily move the power switch to “ON” to cycle through the options. It remembers the last setting. Holding the switch for 3 seconds turns the E6 on or off. Because the switch does different things with long and short activations, and you have to remember the order and/or LED colors, it can be a bit confusing. In my opinion, a power switch should just be a power switch and a dedicated EQ switch, as on the E5 and E11, would have been nice.
NO AUTO SHUTOFF & DESKTOP USE: One of my biggest complaints about the original E5 is the lack of an automatic shutoff of any kind. If you accidentally leave it on, it runs the battery dead. That’s hard on Li-Ion batteries and can easily leave you without a working amp while you’re away from home. Even worse, if you want to use it as a desktop amp plugged into a USB port on your PC, it will still run itself dead when you shut your PC off unless you remember to turn the amp off with the PC every time (or your PC has “stay alive” USB ports designed for device charging). Sadly, the E6 suffers the same problem. I left mine untouched for hours and it was still running and there’s no mention in the very brief operating instructions of an automatic shutoff.
SUBJECTIVE LISTENING: I listened to the E6 with several headphones. With my Ultimate Ears IEMs it has plainly audible hiss but it’s not seriously objectionable with music playing. With my Mee M11+ 16 ohm dynamic IEMs the E6 was reasonably quiet and had plenty of volume but the M11’s already edgy high frequency response sounded even more edgy than normal. I thought I also noticed some harshness with my Etymotic ER4s. But it’s hard to say for sure without a blind test. My inexpensive Sennhesier HD201s sounded about the same as usual but they tend to gloss over flaws. Trying my HD650s resulted in rather nasty clipping on peaks. Unless you listen to highly compressed music, and don’t like it very loud, the E6 is a poor match with headphones like the HD650, HD600, etc.
BASS EQ: I didn’t much like either EQ setting with any of my headphones or music. EQ1 is relatively muddy and bloated. EQ2 is a bit more restrained but still boosts way more than just the deep bass. Both settings seriously “thicken” male vocals. Some, however, might like the EQ—especially if they have really bass shy headphones—like say those you get for free on airplanes. The E6’s EQ came closest to being useful with my sterile sounding Etymotics but even then, with a lot of music, I couldn’t get past the muddy lower midrange and upper bass.
GAIN & OVERLOAD: The E6 has the same 2.5X (~ 8dB) gain as the E11 and O2 on low gain. This should work well for most users. But if you have higher impedance headphones that need a lot of voltage, beware you need a source capable of 1 Vrms to get the most out of the E6. An iPod LOD, for example, is only good for about 0.5 volts. The input overload in the default and EQ modes was around 1.1 Vrms. In the special 2 volt mode, it was about 2.1 Vrms. For more on gain in general see: All About Gain
BATTERY LIFE: I didn’t test the battery life. FiiO rates it at 10 hours. As mentioned above, however, there doesn’t seem to be an automatic shut off. So expect to find the battery dead when you forget to turn the E6 off. Unlike the E11, the battery is sealed inside (AFAIK).
MEASUREMENT SUMMARY: The E6 results are mixed. FiiO improved the low frequency response, low frequency distortion and noise a bit over the E5. But they went backwards on the CCIF IMD high frequency distortion, clipping behavior, and ultrasonic noise. Rumor has it the E6 is based on the same TI chip amp as the E5 so I’m not sure where some of the differences come from (although I speculate in the Tech Section). Overall the two are relatively similar in their performance. The E6 offers a lower output impedance and a bit more output than most portables can manage on their own. But it also may add some distortion to higher quality portables like the iPod Touch. Here’s a summary and comparison table:.
|Measurement||FiiO E6||FiiO E5||FiiO E11||O2||AMB Mini3|
|Frequency Response||+/- 0.5 dB A||+0/-3 dB C||+/- 0.1 dB A||+/- 0.1 dB A||+/- 0.1 dB A|
|Phase Error 100-10K||4 deg||N/A||4 deg||< 1 deg||< 1 deg|
|THD 1 Khz 150 Ohms||0.008% A||N/A||0.004% A||0.0016% A||0.002% A|
|THD 1 Khz 15 Ohms||0.03% C||0.012% B||0.011% B||0.0023% A||0.017% B|
|THD 20 hz 15 Ohms||0.1% C||0.7% D||0.017% B||0.0023% A||0.01% B|
|THD 10 Khz 15 Ohms||0.04% C||0.05% C||0.011% B||0.010% A||0.45% F|
|IMD CCIF 15 Ohms||0.006% C*||N/A||0.002% A||0.001% A||0.043% D|
|IMD SMPTE||0.019% C||0.006% A||0.0079% A||0.002% A||0.009% B|
|Noise A-Wtd||-95.2 dBu||-93.8 dBu||-101.3 dBu B||-114 dBu A||-103.2 dBu B|
|Max Output 15 Ohms||122 mW A||108 mW A||63 mW B||337 mW A||104 mW A|
|Max Output 33 Ohms||59 mW C||N/A||101 mW C||613 mW A||98 mW C|
|Max Output 150 Ohms||24 mW D||N/A||52 mW C||355 mW A||38 mW C|
|Output Impedance||0.25||0.7||0.5 Ohms A||0.54 Ohms A||0.9 Ohms A|
|Crosstalk 15 Ohms||48 dB B||46 dB B||48 dB B||65 dB A||40 dB C|
|Channel Balance||< 0.1 dB||N/A||1.1 dB B||0.6 dB A||1.14 dB B|
|Battery Life||10 hr rated||?||~10 hr rated||~8 hrs / ~30 hrs||~5 hours|
* Note: the IMD distortion letter grades take into account the spectral graph and not just the raw number.
- Seriously small and light
- Very low output impedance
- Some improvements over E5
- USB battery charging
- Falls 25% short of FiiO specs for output power into 16 and 150 ohms
- Lower build quality, poor quality clip, and more plastic compared to cheaper E5
- Single control has 5 functions which is not intuitive and may be confusing
- Alarming levels of ultrasonic/RF leakage of DC-DC charge pump into audio output
- 50% higher price than E5
- Very marginal clipping performance
- Excessively broad bass EQ results in muddy/bloated sound
- Moderate phase error
HEADPHONE COMPATIBILITY: For most headphones with high sensitivity the E5 should be OK. In short, the E6 is best used with headphones rated at a minimum of 108 dB/Volt or 97 dB/mW. If you don’t like to listen very loud, you can subtract up to 5 dB from those numbers. If you listen to wide dynamic range classical or jazz you may want to add 5 dB. For InnerFidelity reviews, the headphones should be rated at less than 0.13 volts for 90 dB SPL. See my More Power article for more details on matching headphones to amps.
BOTTOM LINE: The E6 is not much of a step up from the E5 and in some ways is a step backwards. Overall, they’re fairly similar in most ways. Both are best suited for driving portable low impedance and balanced armature IEM headphones on a budget or when something ultra portable is desired. Both offer a lower output impedance than many portable players and cell phones which is a significant help with balanced armature IEMs. For a tiny $30 headphone amp the E6’s performance is reasonable enough and improves on the E5 in a few areas. But if you’re serious about sound quality, and have headphones around 50 ohms or higher, the FiiO E11 might be worth the extra $35 for mainly portable (but not desktop) use. The E11 can better drive higher impedance less sensitive headphones, has much better clipping behavior, lower distortion on many tests into 150 ohms, much less ultrasonic crud in the output, and much lower noise. For 16-32 ohm headphones, however, both the E6 and E11 have some problems if you’re genuinely concerned about sound quality. For an even cleaner, more powerful, and quieter portable amp that can drive low and high impedance headphones well, you might want to check out the O2 but it’s significantly less portable and more expensive in assembled form than even the E11.
HARDWARE: Rumor has it the E6 uses the same Texas Instruments TPA6130 “chip amp” as the E5 and E7 and despite FiiO’s claim of a “new power amplifier circuit” my measurements seem to confirm it is the same chip. The TPA6130 is rated at 127 mW into 16 ohms when running from a nominal Li-Ion battery as used in the E6. It’s max rating, with 5 volts of USB power, is 138 mW. This makes FiiO’s claim of 150 mW into 16 ohms more than a bit suspicious. As documented below, it only managed 114 mW into 16 ohms on a nearly fully charged battery.
FREQUENCY RESPONSE: The FiiO E5 rolls off the bass to an audible –3 dB at 20 hz. Fortunately, FiiO improved the E6 to where it’s only down an inaudible 0.75 dB at 20 hz. It also has slightly flatter response at 20 Khz for slightly less high frequency phase shift. The channel matching is nearly perfect. There are 4 lots below, 2 for each channel at each load, but they’re all right on top of each other. Somewhat ironically even some high-end gear can’t match the channels anywhere near as well. That’s one of the advantages of using IC’s instead of discrete components:
PHASE ERROR: The goal is less than 1 degree of error from 100 hz to 10 Khz where the ear is most sensitive. The E6 fails to meet the goal at both ends of the audio spectrum. The phase is off by about 4 degrees at both 100 hz and 10 Khz. This isn’t awful, but it’s not ideal either:
1 Khz THD+N vs OUTPUT 15 OHMS: The E6 falls short of its claimed specs. The graph below looks a bit jumbled but shows the E6 vs the $65 E11 and the $150+ AMB Mini3. Interestingly, from about 0.75 volts to 1.25 volts the E6 has significantly lower distortion than either of the more expensive amps. That’s likely because the 3 channel design of the E11 and Mini3 harm their performance into low impedance loads. The max output was 1.35 Vrms into 15 ohms or 122 mW. Into 16 ohms that’s 114 mW which is well short of FiiO’s 150 mW claim and a bit shy of TI’s claim of 127 mW for the chip. The E6, however, outperforms the Mini3 both in overall distortion and maximum output. I tried this test with the E6 running on USB power fully charged and got a nearly identical result—I suspect because the charge pump in the TP6120 is the limiting factor (see: Clipping Performance). Into 33 ohms (not shown), the E6 managed 1.4 Vrms at 1% THD+N for 59 mW:
1 Khz THD+N vs OUTPUT 150 OHMS: Here’s the same test as above except with 150 ohms running on USB power. The results were essentially identical on battery power. Most notable is the E11 has much lower distortion across the board and much higher output into this load. Into the easier load the E6 produced 1.9 Vrms which is 24 mW into 150 ohms and 12 mW into 300 ohms. FiiO claims 16 mW into 300 ohms which is 2.2 Vrms. TI specifies the TPA6130 at 5.3 Vp-p at either 3.6 V or 5.0 V supply voltage. That’s 1.87 Vrms which is very close to the 1.9 Vrms I measured. Given this, and the result above, FiiO seems to be applying some very creative marketing to their specs:
CLAIMED OUTPUT vs ACTUAL OUTPUT: FiiO Claims 150 mW into 16 ohms but, on USB or battery power, the E6 can only manage 114 mW. Even TI only claims 127 – 132 mW for the chip used in the E6. Into 300 ohms, the E6 only managed 12 mW against the 16 mW claimed. In both cases the real output is about 25% lower then FiiO’s spec. Given there’s nothing in the Texas Instruments TPA6130 datasheet to support FiiO’s claims, and my rather black and white measurements, it’s likely another case of creative, and misleading, marketing. This sort of thing is unfortunate as I believe it makes FiiO’s specifications for all their products more difficult to trust.
100hz OUTPUT IMPEDANCE & MAX POWER: At 100 hz the E6’s distortion starts to rise rapidly above 1.23 Vrms into 15 ohms. Removing the load at that level causes the voltage to rise to 1.25V. This works out to a very low output impedance of 0.25 ohms. It’s almost as if the E6 has current feedback as that’s a surprisingly low number. Current feedback senses the output current and uses it to provide an error signal to the amplifier to correct for voltage drop. I measured a more normal 0.7 ohms with the E5. In any event, both are well below the desired 2 ohms which is great:
THD+N vs FREQUENCY: The older E5 had some fairly serious low frequency distortion. Into 15 ohms the E5 exceeded the 0.05% threshold at 200 hz, was over 0.4% at 30 hz, and off the top of the graph at 20 hz. At the same 400 mV RMS, the E6 does better and doesn’t hit 0.05% until 30 hz—that’s eight times less low frequency distortion—and much less likely to be audible. I suspect FiiO beefed up the power supply capacitance, especially on the charge pump, which is likely what hurts the E5. The E6’s distortion into 15 ohms is still a bit bothersome as it’s about 0.03% across most of the spectrum which is above the ideal 0.01% but below the worst case threshold of 0.05%. So it’s overall acceptable but mediocre. Into 150 ohms it’s below the magic 0.01% from about 100 – 2500 hz and rises from there to a modest 0.025% at 9 Khz (it would keep rising if the audio analyzer didn’t cut off at 22 Khz). Into 32 ohms (not shown) it’s around 0.02% through the midrange. This isn’t great performance but it’s better than the E5 at least:
SMPTE IMD 15 OHMS: At the same 400 mV I tested the E5 at, the E6 is surprisingly worse for SMPTE IMD. The “mountain” of E6 IMD products at the base of the 7 Khz signal is much higher reaching up above –80 dB. The THD (harmonics) from the 60 hz signal were similar to the E5. My best guess is the higher IMD is due to the PC board routing/layout, or perhaps the EQ/input level circuitry which is different in the E6 vs the E5. It could also be due to power supply changes. Regardless, this is marginal IMD performance but not unacceptable for a $30 amp:
CCIF IMD 15 OHMS: The E6, not surprisingly, is also marginal on the CCIF test. The first pair of “sidebands” flanking the 19 Khz and 20 Khz signals are well over –80 dB at about –72 dB. The difference signal at 1 Khz is just below –80 dB. Like the SMPTE performance, this isn’t awful, but it’s not great either. As is often the case with IMD, the reading doesn’t tell the whole story. It’s at least better than the AMB Mini3 (I didn’t test the E5 for CCIF IMD):
NOISE: The E6 is a significant 6 dB more noisy than the FiiO E11 and a huge 19 dB more noisy than the O2. But it’s a few dB quieter than the E5. The E5 was 93.8 dBu while the E6 is 95.2 dBu A-Weighted. The absolute noise was about double the E11 at 27 uV. This is acceptable performance but there will be some audible hiss with highly sensitive headphones (including most balanced armature IEMs):
CROSSTALK: By avoiding a three channel design the E6 has respectable crosstalk of –66 dB at 150 ohms:
CHANNEL BALANCE: Unlike my particular E5, which has some sort of channel balance flaw from the factory, the electronic volume control in the E6 (built into the TPA6130 amp chip) had flawless channel balance at any level. It’s hard to even tell, but each of the plots below are really two lines—one for each channel. Even at –45 dB below 400 mV the balance was still within 0.025 dB! There is, however, a bit of odd behavior. The plots below –25 dB were made starting at –45 dB and increasing the volume a single “click” at a time to judge the size of the steps. Most of the steps are around 2 dB but every now and then it jumps by around 3 dB (the wider gaps shown between some lines) up to –27 dB (there are a couple clicks to the –20 dB line). This isn’t a huge problem but sometimes you might find a 3 dB step a bit too much leaving you to choose between a bit too soft and a bit too loud:
GAIN: The E6 has 7.9 dB of gain or about 2.5X—the same as the E11 and O2 set to low gain. This is a good choice for this amp. To obtain the maximum 2.9 volt output it needs 1.16 volts in. But to hit the maximum 1.3 volts into lower impedance headphones, it needs only about 0.5 volts which is the LOD output of an iPod. Beware, however, if you’re trying to drive power hungry higher impedance headphones you’ll need a source capable of at least 1 Vrms output: For more see: All About Gain
INPUT OVERLOAD DEFAULT SETTING: Related to the above is the issue of input overload. Both the FiiO E5 and E7 overload, regardless of the volume setting, with any input much over 1 Vrms. That’s also true of the E6 in its default mode. The graph below shows it overloading with 1.18 Vrms input:
INPUT OVERLOAD 2 VOLT MODE: FiiO provides a “LO 2v high level input” option. To enable it you have to activate the power switch 3 more times after the E6 is already on until the EQ LED turns purple. This feature is not available together with EQ nor is it intuitive. It increases the 1% THD point to about 2.2 Vrms with a fully charged battery and around 2.0 Vrms with a typical battery. This allows using the E6 with normal home sources that follow the Redbook standard of 2 Vrms maximum output. But, as is discussed in the O2 articles, many home sources and even some portable ones exceed 2 Vrms. These are not compatible with the E6 unless they have their own volume control:
EQ: I recently criticized the E11 for having bass boost that reached significantly above 100 hz which tends to result in more “boom” along with the bass boost lower down. The E6’s EQ is significantly worse with a much more broad boost that will still be audible even above 1000 hz. The first EQ1 option (one extra “power on”) results in a red EQ LED (the red plot below) and provides the most dramatic EQ. It drops the upper frequencies by over 3 dB and boosts the bass by nearly 5 dB. The total boost is about 8 dB broadly centered around 75 hz. The EQ2 mode (blue LED and plot) is about a 4.75 dB boost centered at about 50 hz but still over +1 dB at 1 Khz without the high frequency volume drop. The subjective result with most headphones is more boom than deep thump. The E5 had only a single EQ option and it was a more subtle 3 dB boost centered at around 80 hz. For comparison the E5 and E11’s EQ is show in the second and third graphs:
SQUARE WAVE PERFORMANCE: The high speed scope shot below shows the E6 driving Sennheiser CX300 headphones with 0.01 uF of added capacitance. The “thick fuzz” is massive leakage of the DC-DC charge pump in the TPA6130 chip amp. For some reason it’s even worse in the E6 than it was in the E5. It’s much worse on the negative half of the waveform as that’s the half supplied by the charge pump. The sloping sides of the square wave are a clue this is a relatively slow amplifier (more on that below). The only good news here is there’s only a hint of overshoot on the top of the waveform meaning the stability is relatively good (click for full size view of all Agilent scope graphs):
DC-DC CHARGE PUMP NOISE: Here’s a close-up of the “fuzz” from the bottom of the waveform above. It’s a very high 400 mV peak-to-peak which is 140 mV RMS. To put that in perspective, with sensitive headphones that’s greater than the audio signal much of the time when listening at moderate levels! The scope also shows it’s around 770 Khz which is a bit higher than the 400 Khz TI specifies for the TPA6130. So I have to wonder if FiiO has altered the charge pump capacitors which may have changed the operating frequency. They may have made one or more of the caps larger to improve the low frequency distortion performance mentioned earlier. Whatever they did it made the leakage worse. Ultimately, nobody can hear 770 Khz, but one does wonder what it might do to the sound quality when it can be even greater in level than the audio signal. At low listening levels, you’re essentially listening to a modulated 770 Khz RF carrier that’s being “demodulated” by your headphones. As an aside, the E6 not surprisingly wrecks havoc with an AM radio as it’s essentially a low power radio transmitter operating right in the 510 – 1600 Khz AM (USA) band. I suspect there’s no way it can properly pass FCC or CE certification with headphones plugged in acting as an antenna:
SLEW RATE: TI rates the TPA6130 at 0.3 V/uS slew rate. As shown below, the E6 required 9.2 uS to slew from –2 V to + 2V yielding a slew rate of 0.4 V/uS. The rule of thumb is 0.2 V/uS per volt RMS output and the E6 barely meets that requirement. So, however slow and ugly the square wave might look, the E6 shouldn’t slew rate limit with any music signal you’re likely to feed it but it’s at the bottom range of what’s acceptable:
CLIPPING PERFORMANCE: The E6 had highly asymmetrical clipping even into a very easy 600 ohms with the negative rail clipping far sooner than the positive rail likely because the positive rail is direct from the Li-Ion battery and the negative rail is from the DC-DC charge pump built into the TPA6130. If you look close you can see the “digital phosphor” feature of the Agilent scope revealing the actual clipped waveform under all the hash on the negative side. Because this is worse than the E5 it’s a further clue FiiO may have altered the charge pump circuit—in some ways for the worse—with the E6. To be blunt, combined with all the charge pump ultrasonic garbage, this is the worst clipping performance I’ve ever seen from a headphone amp. This is only likely to be an issue if your headphones will push the E6 near its output limits. You won’t, for example, get close to clipping with most balanced armature IEM’s (Shure, Etymotic, etc.). Matching headphones to amps is further explained in my More Power article. For comparison the E11’s performance on the same test is shown in the second graph (click for larger):
TECH COMMENTS: In some ways FiiO improved on the E5 with the E6. The low frequency response is flatter, there’s significantly less low frequency distortion, a bit less noise, and there’s a special mode to allow a 2 Vrms input. But, on the negative side, the E6 has less useful EQ, even more ultrasonic garbage (at a frequency and level the FCC and/or CE might not approve of) leaking into the output, and significantly worse clipping behavior. The E6 also fails to meet FiiO’s power output specs, and assuming it really does use the TI TPA6130 chip, the datasheet indicates it’s unlikely it ever could reach their claimed power levels under the best of conditions. The E6 is not an especially clean or well behaved amplifier but in light of the very modest $30 price it’s likely acceptable for many applications for those on a budget. It would be interesting to conduct blind tests against the O2 and see how it compares and if perhaps there are some audible side effects to the large ultrasonic/RF output and other flaws.