Objective Reviews & Commentary - An Engineer's Perspective

November 23, 2011

FiiO E6 Amp

fiio e6 package dscopeINTRO: 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.

fiio e6 e5 ipodNO 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).

fiio e6 dscope ipodMEASUREMENT 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:

FiiO E6 Frequency Response Both Ch 16 Ohms (blue) 150 Ohms (yellow) Vol=Unity 400 mV


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:

FiiO E6 Phase Response 150 Ohms Vol=Unity 400 mV


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:

FiiO E6 1 Khz THD N vs Output 15 Ohms vs Mini3 (yellow) & E11 (orange)


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:

FiiO E6 1 Khz THD N vs Output 150 Ohms vs Mini3 (yellow) & E11 (orange)


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:FiiO E6 100 hz Max Output & Impedance 15 & 100K Ohms


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:

FiiO E6 400 mV THD N vs Frequency 15 Ohms (blue) 150 Ohms (yellow)


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:

FiiO E6 SMPTE IMD ~400 mV 15 Ohms (ref ~ 400 mV)


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):FiiO E6 CCIF IMD ~400 mV 15 Ohms (ref ~ 400 mV)


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):

FiiO E6 Noise Vol=Max Ref 775 mV (dBu)


CROSSTALK: By avoiding a three channel design the E6 has respectable crosstalk of –66 dB at 150 ohms:

FiiO E6 Crosstalk 150 Ohms (ref ~400 mV)


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:

FiiO E6 Volume Steps & Tracking (ref 400 mV)


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

FiiO E6 Gain Vol=Max 150 Ohms (ref 0225 mV)


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:

FiiO E6 Input Overload 150 Ohms (ref ~400 mV)


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:

FiiO E6 Input Overload LO 2V Mode 150 Ohms (ref ~400 mV)


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:

FiiO E6 Freq Response EQ OFF (yellow) EQ1 (LED red) EQ2 (LED blue) Vol=Unity Ref 400mV

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

FiiO E11 Frequency Response EQ=2 EQ=1 EQ=0 Top to Bottom


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):

FiiO E6 10 Khz Square Wave CX300   10 nF 2Vp-p


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:

FiiO E6 DC-DC Converter Noise 400 mVp-p at ~ 770 Khz


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:

FiiO E6 10 Khz Square Wave & Slew Rate 600 Ohms (just under clipping)


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):FiiO E6 10 Khz Sine Wave Clipping Performance 600 Ohms

FiiO E11 10 Khz Sine Wave Clipping 600 Ohms


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.


  1. Yuck. A bit of a messy execution in that box.

    Have a safe and happy thanksgiving!


  2. Thanks for another great article. I stumbled on your blog after googling udac2 channel imbalance after hearing it with mine. Honestly you're my hero. Not just for exposing them, but also for building O2.
    So you think it's bad to pair it with Grado RS1, making it more harsh on the upper end? I'm struggling to find an affordable amp for them and I don't care much about portability. My understanding is that MrSlim is not building O2 any more. Is there any other way to get a built one? Or do you have another recommendation?


  3. I've found that the E5 clip feels solid and reliable long-term, but doesn't actually clip that strongly. Many people don't use the clip anyway.

    Also the position of the buttons:
    back - input, USB mini-B charging
    front - headphones out, volume, power, EQ

    is not that good. With thicker headphone jacks, the volume control is almost partially obstructed. Then you try to turn it off (without looking at it), but accidentally hit volume up, since they're right next to each other.

    So I have no idea about the clip on the E6, but at least it's detachable, and the volume control seems to be in a better place.

    Aside from the weird EQ / on switch control (and move from metal to plastic), I think the E6 may be more of a functional improvement to the E5 more than anything else. Working with higher-output sources sounds good to me. Portable amps are probably a good way to "add" a headphone jack to something like a TV that may not have a headphone output, and I suspect many of them would clip the E5 but not the E6.

    The actual electrical performance issues are kind of disappointing though, that's for sure.

    A happy Thanksgiving to you, though I suppose in "northwest" that may not be until another hour or two.

  4. I can hear my headphones cracking by just looking at that EQ. :o

  5. Just wanted to quickly point out that Fiio claims the clip is made out of higher quality polycarbonate, not standard ABS plastic. According to them this should mean it is not very likely to break - I've seen pictures of it being stretched a ton without breaking either, so I'm inclined to believe this.

    Looks can be deceiving!

  6. Nwavguy, my E6 remembers its EQ/gain state after turning off, there's no need on mine to switch to the 2VRMS each time its turned on. Mine also has noticeably less hiss than the E5, even with the most ridiculously sensitive IEMs (SE530, UE11).

  7. @dfkt, Thanks for the correction. You're right. I thought it reset when it was powered off but it does remember the setting. I've revised the article.

    @wcesharp, Thanks for added info on the clip. I just abused one and you're correct, they seem fairly durable. I've revised the article.

    @mikeaj, the controls on the E6 are spread out more and easier to use without looking at it. But the multi-function switch and EQ LED on the back are still poor ergonomics. I've revised the article to add some of your points.

    @Anon, Epiphany in the UK is selling assembled O2s and there should be some more sources soon. Some are doing small batch builds to use up extra boards/parts they purchased from component group buys. And others are talking about perhaps stocking assembled boards. Anyone who can use a screwdriver can assemble an O2 from a pre-assembled PC board. Check the existing links in the O2 Resources section and check back there now and then for updates. You might also want to post on some of the forum threads listed there.

    @heycarnut, Happy Holidays to you, and everyone, as well!

  8. Wow. I almost got one of these but it won't supply the power I was hoping into my AKGs. Thanks for this article!

  9. hey nwavguy..i'm curious if you have ever, or would be interested in measuring more expensive DACs or amps.. e.g. like the dacmini, anedio, or the more expensive amps like the zana deux, gs-x, etc... it'll be interesting how do the big boys measure up..

  10. @akgk171, you're welcome.

    @Anon, As for more expensive DACs, you'll find lots of measurements of my $1600 Benchmark DAC1 Pre sprinkled around this blog and a write up on it as well.

    In my opinion, if a DAC cannot support 24 bit over USB to allow use of software volume controls without compromising performance, it's not worth reviewing unless it's very inexpensive such as last six DACs I reviewed.

    A lot of DACs are in transition right now. Anedio stopped making their DAC (which didn't even support USB). Emotiva is closing out the impressive XDA-1 to make room for a new model that will support 24 bit over USB. MF has replaced the 16 bit USB V-DAC with the 24 bit V-DAC II. HRT has a new DAC coming. Even FiiO has the new 24 bit E10.

    You don't have to spend $1000+ to get fully transparent DAC performance where the DAC contributes no sound of its own. It's been demonstrated DACs can be fully transparent in blind listening tests if they measure sufficiently well. Meyer & Moran demonstrated this in their large blind listening trial published by the AES. It's also demonstrated in the Matrix Audio testing linked in the right hand column of this blog. At Matrix the DAC in a really cheap Sony CD player sounded just like the one in a high-end Wadia.

    Put simply, a lot of the high-end DACs on the market are a big waste of money if you're buying them thinking you're getting better sound quality. And many likely perform worse on a test bench than the $300 Centrance DACport--especially the ones with performance degrading marketing gimmicks like vacuum tubes, etc.

    I'll soon be publishing my most complete DAC measurements yet for a relatively inexpensive DAC that supports high resolution 24/96 over USB. I helped design it and its first application will be as an optional daughter board to the upcoming desktop version of the O2 headphone amp (the "ODA"). I'll put it up against my Benchmark DAC1 in blind testing and see what happens. If it sounds as good as the DAC1 I'll wager it will also sound as good as an Anedio, etc.

    The other problem with testing expensive gear is getting it. Manufactures don't exactly love me as, unlike the regular review sites and magazines, they have no influence over me with ad revenue, etc. And the anonymous nature of this blog doesn't help either.

  11. I think it's safe to say that FiiO is definately using the TPA6130A2 chip. TI once listed the 6130 at 150mW but lists the current chips at 138mW. Nothing else I found comes close to those numbers and still has a charge pump, so it can't be anything else with any probability.

  12. Thanks for another great review. Are you planning on reviewing FiiO E10? I just got one this morning and I did A-B comparison with the udac2. I'm listening through a Grado RS1 and with the udac2 there is annoying distortion for the snares and metal string guitars (not sure if that's what maps to your measurements) . E10 sounds much cleaner in comparison and no channel imbalance that I can detect at all. Very high gain though, at 2 or 3 (from 8) it's pretty loud. Have't tried it yet with my Shure SE530 yet but I'm expecting my ear drums to blow if I attempt that.

  13. Hisham, I am planning an E10 review. I'm not surprised it sounds better than the flawed uDAC-2.

  14. hey..it's interesting that you mentioned the dacport in the previous comment.. have you measured it?? i cannot find it on your site.. is it also one of those that measures well??

  15. @Anon, I haven't measured the DACport but Stereophile has and it did fairly well. I also, indirectly, know some of the talent behind Centrance and they take a much more engineering oriented, and rational, approach to DAC design than many audiophile makers who seem more interested in chasing various FOTM fads, chips, etc. Centrance also responded to my criticism of their 10 ohm output impedance by offering 1 ohm versions of their products on request. Finally, the Centrance high resolution USB technology is used (under license from Centrance) in my Benchmark DAC1.

  16. Bass is still much better sounding to me on it over the E7. I wonder if the IMD you found on it is responsible for the slightly glassy, edgy quality it has over the E7. Did any of the other measurments improve in the low-gain, high-input mode... other than clipping?

    Did you manage to grab a 0204 when it was on sale for under $70?

  17. @Reticuli, I didn't test other parameters in the high input mode but I'll try to if I get the chance. I really doubt much changes but it's possible. The E7 and E6 use the exact same TI chip amp and have very similar performance. Besides differences in EQ, I suspect any difference you're hearing is either due to something else or is imagined. If anything, the E7 measures slightly better than the E6. Most notably the E7 has less ultrasonic crud in the output.

  18. This is currently on sale at head-direct.com for $22.99.

    I bought one and look forward to comparing it to the O2.

  19. thanks on your reply regarding the dacport. now i have a couple of questions in mind..
    do you think power supply plays a big role in the performance of dacs or amps?? i remember Jason of Schiit mentioned in a head-fi thread that his bifrost should not be compared to usb powered dacs in the price range because..well, they're usb..
    also, what do you think about the dacport and dacport lx?? if the regular dacport is used as a dac only, then the output signal is already amplified, would it hamper the performance compared to the dedicated line out in the dacport lx??

  20. Hi NwAvGuy,

    I have listened to different players with my and E7 and E9, like Fidelia, PureMusic, Decibel and Amarra, and although the differences aren't night and day (I guess it's another story with a 24Bit/96-192 DAC), they are still audible.
    I believe it would make sense to take a look at the players and their performance and features, since they're also part of the audible results of listening chain. In this sense, I wanted to ask if you have considered taking a look at different players in the future (and if that makes sense to you)?

    Thanks a million for sharing with us all.

  21. @Anon #1, the line out Dacport might have a slight advantage in terms of measurements but I suspect it might be hard to hear the difference. It's worth checking out my More Power article and figuring out if the 1 ohm version of the headphone Dacport can directly drive the desired headphones and then no amp is required.

    I'm not sure what Jason at Schiit is trying to say but that's nothing new as he seems to talk in marketing-speak (i.e. the Asgard transient problems). It's fair to compare to Bifrost to any DAC around the same price or less. Why not? There are ways to make USB power work very well. I'm fairly comfortable the upcoming 24/96 DAC for the desktop version of the O2 (ODA) will roughly match or beat the Bifrost on a test bench and match or beat it in blind listening tests as well. And it will do so for a lot less money. I would also put the Dacport up against the Bifrost while the DacMini has way more features and probably outperforms the Bifrost.

    Anon #2, I hate to say it but unless you have EQ or some other processing enabled, there are not likely any differences between software players. Most of the decent ones are capable of bit accurate audio. And, by definition, bit accurate audio will all sound the same. Most players don't actually do the heavy lifting of playing the tracks. They simply make API calls to the operating system or an audio/media API that does it for them. Hence most are using the same code for that functionality. I would suggest reading my Subjective vs Objective article if you haven't already. It's very easy, and common, to imagine hearing differences that are not really there (for example, see the McGurk Effect video).

  22. What difference does ultrasonic crud make on most headphones? Don't the transducers act as low-pass filters?

    Have you ever tried testing an electrostatic amp?

  23. @Reticuli, I can't say at this point what difference the ultrasonic crud makes. There's no question it's not a good thing. Headphones, combined with human ears, are indeed a low pass filter. But that doesn't mean the ultrasonic noise is entirely inaudible. For example, the audio signal may interact with the ultrasonic frequencies and form difference signals within the audio band much as happens with the CCIF IMD test. In that test the 19 Khz and 20 Khz tones can form an audible 1 Khz distortion component. Something similar could happen with the E6 significant ultrasonic crud and the audio signal.

  24. thanks..your blog has been a great resource for many audio enthusiasts, including me.. I'm looking forward to your ODA.. any ETA on it??
    also, you said that a USB powered devices could perform as well as another one with a dedicated power supply.. but why do ppl always ramble about beefy power supply, like the gilmore lite+DPS is said to be better than without it (at the cost of twice the glite itself). or the apex peak and arete amps, todd is selling the volcano power supply for about $700 to improve the sound.. is it really matter or is it just exaggerated?

  25. @Anon, some inherently poor amplifiers, especially singled-ended MOSFET amps like the Schiit Asgard and single ended triode tube amps, can benefit from better power supplies because they are unusually sensitive to power supply noise and ripple. But properly designed amplifiers with decent Power Supply Rejection Ratio (PSRR) just need a supply that's reasonably low noise and can supply enough voltage and current.

    With a decent amp, "upgrading" the power supply beyond the basic requirements won't make any difference in the performance. It's a classic case of another audiophile myth with a grain of truth behind it.

    The bottom line is nearly any amp that can genuinely benefit from a power supply upgrade is likely a seriously flawed design. You would nearly always be much better off spending your money on a properly designed amplifier instead. But many of the power supply "upgrades" are pure snake oil and close cousins to Sonic Bricks, expensive cables, fancy power cords, vibration isolators, etc.

    I plan to announce more ODA details in December and anticipate releasing the documentation package to build one in the first quarter of 2012.

  26. "I'll soon be publishing my most complete DAC measurements yet for a relatively inexpensive DAC that supports high resolution 24/96 over USB. I helped design it and its first application will be as an optional daughter board to the upcoming desktop version of the O2 headphone amp (the "ODA"). I'll put it up against my Benchmark DAC1 in blind testing and see what happens. If it sounds as good as the DAC1 I'll wager it will also sound as good as an Anedio, etc."

    That's just awesome. :)

  27. Thank you so much for all your painstaking work. Coming into hi-fi with very little understanding of electronics, I have learned so much from reading your articles and reviews to help me figure out what really affects SQ and what my best equipment options are. Thank you!

    After reading your reviews of the E7 and E5, I decided to get the E6—just before you reviewed it! A mixed bag, it seems.
    A couple questions about the E6 with my setup and about configuring sources with an amp:

    I've got Fischer DBA-02 IEMs (108dB/1mW, 43 Ohms) and Grado SR-80 cans (98dB/1mW, 32 Ohms), which I use with my iPhone 4, Sansa Clip Zip, and Macbook.

    1. Would the loudness or quality of the output from the E6 be marginal with either the Fischers or Grados? From what I've read the Grado's will require quite a bit more power with 11dB lower sensitivity but should get up to the 110 range and be marginally safe from clipping, unless I'm misunderstanding. I usually listen at moderately high volumes.

    2. I've read about configuring digital sources for bit-perfect output, so I've got that covered. But I don't understand how the analog output of computers and portables can affect SQ when put through an external amp. I've got a line out adapter for the iPhone, so that's covered, but how should one handle the volume settings of the source+amp? Max the source and and only adjust the amp volume? Vice versa? Or keep the source in the middle range and adjust the amp as needed? This is assuming the E6 amp is in most ways at least better than the source's amp, which maybe I am wrong about.

  28. The E6 should produce reasonable levels from the Grados. One could argue either of those headphones might deserve a slightly "cleaner" amp than the E5/6/7 but that's debatable.

    The source volume issue is tricky. The LOD on the iPhone is easy as it bypasses the volume control (as it does on iPods as well). But the PC volume is a different matter. I would suggest leaving the PC's volume at about 80% - 90% and then set the volume on the E6 for the desired listening level. While you ideally want the PC's volume all the way up for an external USB DAC so you get a bit accurate stream, 100% may cause clipping, or at least higher distortion, via the PC's line/headphone output.

    The E6 likely has a lower output impedance and a higher output power than your PC. Some PC's are fairly awful when trying to drive headphones directly.

  29. Thanks! After some A-B listening with the Grados from the PC directly vs. through the E6, the PC vol. was near max and was possibly clip, your suggestion is confirmed: the PC volume was near maxed and possibly clipping, while the E6 had plenty to give and sounded slightly better.

    I had read that keeping max volume preserves bit-perfect digital output, but is that relevant when feeding analog output from the jack to an analog amp input? Wouldn't the priority in this case be to set the volume to minimize the PC amp's distortion (thus your 80-90%)? Does using an external amp without LOD or DAC really just compound the various distortions of the two amps, or does a downstream amp clean up any of the source distortion?

    Based on your review I can see how a better amp would be justified. Your O2 would be great if a little overkill, and a very fun project, but I've never soldered and I'd have to learn to read schematics. I'll have to keep checking for group buys of assembled units.

    Again, thank you so much for all your work. I hope you enjoy doing it as much as your readers are benefiting from it!

  30. I should revise the O2 summary article. JDS Labs is selling pre-assembled O2 boards for $90 in their e-store. No group buy required. You don't need to even own a soldering iron. You just slip the board into the case and use a screw driver to attach the front and back panels. See:

    O2 Files & Resources

    I would suggest reading my February article about Amps/Dacs as well as the September All About Gain and More Power articles.

    An external amp can lower distortion because it represents a much easier load for your PC's analog output to drive compared to headphones. Headphones might be 32 ohms while an amp's input might be 10,000 ohms. That reduces the required current by 100 times or more which can significantly lower the distortion of the PC's output.

    An external amp also, as already discussed, lets you run the PC below its maximum output for lower distortion as well.

  31. Thanks yet again. I had not checked the O2 resources page in awhile. I did read the suggested articles but it's all so new I need to read them a few times to tie it all together. I'll go with your suggested handling of source/amp volumes until I feel the need for a DAC and a higher grade amp.

  32. I have allready ordered an O2 from Mr. Slim, the portable version. I wonder if your upcoming DAC can be connected to the portable O2 and a computer? And will it be preassembled?

  33. @Anon, that's the plan. The DAC board will be pre-assembled and tested.

  34. That is great news! And I really appreciate what you are doing for the Head-fi community. I visit your blog several times every day.

  35. NWAVGUY is spot-on. I purchase the CEntrance DACmini after reading his blog comments. I previously owned a E7. A month later, DACmini was on stereophile Dec front cover. Can't wait for my O2 to arrive.

  36. My E6 arrived today and it sounds less good so far, all fuzzy and lacking.

  37. Hi NWAVGUY,
    I have some doubts which Im pretty sure you can cover. Fisrt of all Im not rich. Im using a sony walkman bseries. Im planning to chuck iems and go for headphones. so obviously It needs more juice than iems. I have narrowed out on two choices j3 or ipod touch. i dont care anything but sound quality. All i expect is enough power to drive the headphones really loud. Not that i hear it loud all the time but for some songs at times you feel you need to have it in full blast. I am not a fan of in ear headphones, so i need a high amp device to power vmoda m80s which i plan to buy. my question is, should i save the money and go for fiio amp to work with my sony b-series walkman and chuck the whole idea of getting a new player? which will save me from buying a new player.
    These are the specs of b-series walkman
    Maximum Power Output (16 ohms/mW) 5+5mW

  38. @Aki, the iPod Touch will have the best sound quality and it would be close as to if it or the Cowon J3 has more output--the J3 might win that part of the fight but the iPod will likely have the better DAC, flatter response, and lower noise. Forget the Sony players. All the ones I've tested, or have seen valid tests for, have really weak headphone amps in comparison.

    If you pick the right headphones the iTouch will have plenty of output and is vastly more sexy, versatile and easier to use than any Cowon. You can also get tons of accessories for them very cheap. See my More Power (or ask around on the forums) to figure out which headphones will well with the iTouch.

    Also look at the Sansa Clip Zip (or Clip+). Again, with the right headphones it won't need an amp and sounds great. It's also cheap and great for using on the go. See my Clip+ review.

  39. Thank you nwavguy,
    It will be a day or two while i figure out your more power blog. but it helps. I am sorry about the posting on another blog. i though this one didnt go through with multiple attemps to post it.

  40. There are lots of decent sounding yet relatively efficient full size cans like many of the Denon and Grado models. Anything 32 ohms or lower rated at 100 dB/mW or higher will be OK. Or anything at any impedance rated at more than 115 dB/V. Or anything InnerFidelity rates less than 0.05 volts for 90 dB. All of those will get fairly loud with even the $30 Clip Zip/+.

  41. Which one is louder? sansa clip+ or ipod touch. I tried using the ipod touch with the klipsch image one headphones rated INPUT IMPEDANCE: 32 ohms
    SENSITIVITY: 110dB(for it being the only headphones for display), at the store today, but it was not loud at all! comparing it with the sennheiser cx180 iems I use now. Which makes me wonder should I just stick with the iems even though they are terribly uncomfortable.

    Thank you NwAvGuy

  42. @Aki, I'm not sure if you were just playing a soft track on the Clip+ or if you're into serious hearing damage "loud". But the Image Ones should easily hit peaks of 110 dB with the Clip+. InnerFidelity tested them and found they need only 0.049 volts to hit 90 dB. That means 0.49 volts for 110 dB. And that's about exactly what the Clip+ puts out.

    Most pop/metal/etc. music has a peak to average ratio of 10 dB or less. That means if the peaks are hitting 110 dB the average level is at least 100 dB. Anything over 85 dB sustained causes hearing damage. There's more info in my "More Power" article but most would consider average levels of 100 dB very loud.

    This is also getting way off topic for this FiiO E6 article. Good luck in your search.

  43. Hey NwAvGuy!

    I find your articles well written and really objective especially when it comes to measurements. I haven't seen anyone being so objective in reviewing audio equipment. I was wondering if you could publish your data in a scientific journal. And thank you for building the O2 amp. I hope I could get my hands on a pre-assembled or ready to use O2 amps here in the Philippines.

    By the way, have you heard about the digiZoid Zo headphone amp? They cloud the principles as to how the amplify the sound. I was hoping you could shed a light on this and dissect one of the Zo amps. Here's the link to their website: http://www.digizoid.com/tech/

  44. DigiZoid just seems to be yet another "branded" form of DSP much like BBE, SRS, etc. They mainly seem to be selling a shortcut for manufactures wanting to offer custom tailored DSP for their products. For example, a gaming headset maker could outsource the DSP work to DigiZoid.

    But, pending patents and marketing hype aside, I really doubt there's much "revolutionary" in their approach. The world of DSP--including frequency, time/phase, and dynamic processing-has been fully exploited and well documented. It's a lot like combining different amounts of mayonnaise, red sauce, and a handful of spices to create a new "secret sauce" for hamburgers. The raw ingredients have been around forever and there's nothing revolutionary about combining them in ways that are slightly different.

  45. Thanks for all your articles, they rock! You are truly authoritative and unbiased and that is excellent.

    Well, I just got the Beyerdynamic DT770 Pro 80 headphones to use with my iPod Touch 3rd Gen. This works just "well enough" as some songs could use a boost as I have to turn the volume up all the way. So I was wondering what amp would make my setup even better? I am thinking about the E5 and E6, but wanted to get your opinion on what would work the best for the least $$$ for an amp in my situation. Will the E5 or E6 increase the volume and quality so I don't have to turn the volume up all the way, without bad side effects?

    I don't think it is an absolute "necessary" to get an amp for the DT770s, but if it increases quality and volume, then it might be cool to have.

    Thanks again!

  46. I have the DT770 Pro 80, a Touch 3G, and the E6. You only get about 1.25 volts out of the E6 and, into the 80 ohm Beyers, the Touch can already manage about 1 volt. That means the E6 is only about 2 dB louder. While that's noticeable, it's not night and day. And the amp in the Touch is better, and quieter, than the E6 so you're taking a step backwards in some ways to use the E6.

    I would strongly suggest spending a bit more for the E11 if you really want an amp for the Beyers. The downside is it won't run from USB power like the E6 will. If you want it more as a desktop amp, I'd get an O2.

  47. Currently I'm using the PSP which sounds rather bad with the Klipsch X10s, I'm wondering if I should get the E6 or E11 or just get a phone/player with a good internal amp. Want your opinion on this. Thanks.

  48. @Question, it's your choice. The Clip+/Zip is a great player for the price and much easier to take with your than a PSP when you're not also looking to game. But if you always have the PSP with you anyway, get an E6 or E11. I can't promise adding an amp will cure all your sound quality issues, however. The PSP may have other problems with its headphone output.

  49. Is the charge pump noise present when there is no input or if the output is less than 1Vp-p?

  50. The charge pump noise is always there.

  51. You should have disassembled the unit to verify the chip (TI TPA6130) as you mention. Really, no disassembling. After all its just a 30 dollar amp, what's the risk?

  52. I am wondering if I could connect my iRiver PNP up to it and plug the out connection into my Sony Amplifier to boost the sound levels from my iRiver player? This way I could play the flac files on my small media player over my loud speakers.

    1. Generally it's not a good idea to add more stages of amplification than are necessary. Your iRiver can probably be connected directly to your Sony amplifier even if it means turning up the volume more on the Sony.

  53. I just bought E6 and have been trying it out with either my iPhone 4 (Line out) or Macbook pro. When used with Macbook pro I hear a lot of static except in the EQ3 setting. So, Macbook pro audio works only with EQ3 on E6. But I am having a bigger issue with E6. When I connect it to my iPhone using a Line Out cable and use Ultimate Ears 700 IEMs, I always hear a lot of static in all the EQ settings. What might be going on? There is no static when used with Beyerdynamic DT770 Pro 80 or AKG Q701? What might be wrong here? I thought E6 worked well with sensitive IEMs.

    1. If your Ultimate Ears came with an in-line attenuator (mine did) you might want to use it if you're hearing noise. I didn't test the signal to noise performance of the E6 with the EQ enabled. It might be FiiO did a lousy job with the EQ circuit. Because balanced armature IEMs are ultra-sensitive you're much more prone to hearing any noise problems in the signal path. See: Noise & Dynamic Range

  54. I just bought this e6… I read the power output for 16 ohm impedance is 150 mw… I use IEM soundmagic e10 and maximum input for this IEM is 20 mw… will this amp damage my IEM? thanks in advance

    1. It's unlikely you will damage your IEMs with the E6 but you may want to use care with the volume control just to be safe.

  55. hello sir will you help me to decide between e6 and fiio e11. im using sennheiser hd-419 and a nokia n8 12 megapixel smartphone.. im having a hard time deciding and reading reviews and choosing between the two amplifiers. im looking for a more balanced sound and yet powerful amplifier to drive my sennheiser hd-419.. im not looking for skullcrushing bass as the 419′s bass is good enough and needed just a little more..so im wondering which of these two amplifiers will you reccomend that have a more balanced sound and gives more power, clarity or soundstage to sennheiser 419..is the equalizer of these 2 amplifier just gives bass boost or it gives treble as well….which one will you reccomend the e6 or the e11? and lastly im confused..a smartphone has an equalizer and a portable amp has an equalizer, when playing the headphones which equalizer that the headphones uses , is it the eq of the amp or eq of the smartphone or both (if the headphone bypasses or uses the eq of the ampli then the eq of the phone will be useless)im confused.. thanks and more power. sorry for the many questions and the inconvenience, i just want to be sure on my purchase and will not make a mistake on which portable amplifier im going to pair with my hd 419…

  56. Does the battery have to be charged through a usb port on a computer?

    1. Or any 5 volt USB charger (they're $2 on eBay).


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