Fiio K5 Desktop Headphone Amplifier

Pros: Price to quality ratio; K5 allows for docking with FiiO DAPs; Plug and play; aesthetically pleasing; Low output impedance; Three gain settings
Cons: Power output will struggle with some inefficient planars;

The Good: Price to quality ratio; K5 allows for docking with FiiO DAPs; Plug and play; aesthetically pleasing; Low output impedance; Three gain settings
The Okay: Power output will struggle with some inefficient planars;
The Bad: No stated power at 600ohms, but likely not very high based on 150mW at 300ohms
Tonal Balance: Mildly warm leaning
Listening Set-Up: Musicbee (WASAPI+FLAC) -> E17k/K5 -> Various headphones
Cost: K5: $110, E17k: $140

Reviewing Process

The FiiO K5 and E17k were sent to me from FiiO as a review unit. I have had the combination plugged into my computer and kept running for the entirety of my time of possession, approximately one month as of now. I have tried a variety of headphones with it with some notable headphones being the Audio Technica AD2000, RHA S500i, ZMF Omni, and Sennheiser HD600. I have the Schiit Magni 2 Uber & Schiit Vali 2 (connected to the Modi 2 Uber) and the Matrix HPA-3u that I’ve done AB testing with to compare.
I feel comfortable sharing my opinion on these two products due to my time and experience with them, but I always recommend demoing a product first-hand to form your own opinions.

Build Quality

FiiO K5
The unit is housed in some sort of metal chassis which feels rather lightweight given the size of the unit. The volume potentiometer is large and turns cleanly and smoothly, actually a nice feel to it when turned. All of jacks are secured and offer no issues when used. When the E17k is docked it is seated nicely.


FiiO K5
Despite the USB out, the K5 does not have an integrated DAC, it’s used as a bridge for a docked FiiO product. It does feature RCA line-out and line-in, as well as 3.5mm balanced out. The docking feature is the biggest draw on the K5 in regards to features, this allows for existing FiiO products with a DAC to be docked into the K5. Other DACs can be used, but the major draw is the capability to work seamlessly with existing FiiO products.

Power Output & Impedance

FiiO K5
The power output peaks at 1,700mW at 16 ohms with a published 150mW at 300 ohms with a published output impedance of less than 1 ohm - low enough to have a high damping factor even with low impedance IEMs. I am unable to find output power at 600 ohms, but I’m not very optimistic of it outputting enough power at 600 ohms to be considered for headphones at that impedance. FiiO seems to agree, in the specifications the K5 is specced for 16-300 ohms.
The K5 has no issues with low impedance and high sensitivity IEMs like the RHA S500i with no noise floor until volumes that would likely kill the driver if music played through them. The K5 powers the Audio Technica AD2000 without a hitch, though that’s to be expected based on their impedance and sensitivity ratings. The HD600 get close to being maxed out with some recordings, but most users will find plenty of headroom here. The K5 does struggle with the ZMF Omni though, which sit around 55 ohms and between 90-94dB/mW. High-gain is a must for the Omni, and some recordings simply don’t get loud enough with this set-up.

Sound Quality

FiiO K5
In my listening and comparisons I find the K5/E17k combination to have mild warmth without sounding veiled. Slightly smoothed over in details, but very easy to listen to as opposed to the Schiit Magni 2 Uber which I find to be a little bright in comparison. I notice no signs of distortion, nor any added grain. Overall a very nice sounding amplifier for the price when docked with the E17k.


The K5 is a no brainer amplifier if you’re integrated into FiiO’s ecosystem and don’t have huge power requirements. It’s closest competitor would be the Magni 2 and Modi 2 combination, which offers a stronger maximum power output and less vertical space real estate making it easier to sit beneath a shelf, for instance. I prefer the sound of the K5 with the E17k unit though, it’s not as detailed as the Schiit stack, but it lacks the treble grain that causes fatigue over long-term listening and presents music in a slightly more euphoric manner.
The K5 is a wonderful amp if you have a FiiO DAP or portable DAC that can be docked into the K5. If you’re buying a DAC and an amp from scratch then I think that the Schiit stack is a better value due to the added output power making it a little less replaceable if you move onto power hungry planars.


New Head-Fier
Pros: Output power, 3 steps gain, smooth presentation
Cons: Restrained dynamics
I use this desktop amp more than a week and here is my quick review.
I mostly use this gear combination : Fiio X1 + iFi iCan nano + Audio Technica R70X
For K5 testing purposes : Fiio X1 + Fiio K5 + Audio Technica R70X or MSR7
I tested only with the top side USB dock connector. Mid gain with R70X and low gain with MSR7.
The amp build quality is in pair with other Fiio devices, well built but not premium level.
The SQ is definitely better in every aspects than the X1's built in headphone amp. This is not a surprise of course. :)
Compared to the iCan nano : 
The K5 have a little bit less dynamics and zing at the upper regions but better performance at the lower end.
The high impedance (470 ohms) R70X's bass is grateful for the bigger power and give you more enjoyable lower frequencies.
With the lower impedance (35 ohms) MSR7, the K5 don't have this extended bass but successfully reduce the elevated upper mid character of the headphone and produce much less hiss than the nano.
Overall :
This amp is very well balanced, powerful and smooth but detailed sounding.
If you have a newer Fiio DAP and want a good price/value ratio desktop amp, go for it!
Pros: Transparency, build, value, gain, power, pairing versatility
Cons: Rear line out is fixed, 11 pin micro dock could be a weak point, should include micro-USB to micro-USB cable
To view images fill size (1200 x 800), simply click any image in the review


For many newcomers to portable audio, especially in this community, Fiio has been a good choice for their portable audio players, and also their amps and DACs.  They have a very good range of product from entry point through to top of the line.  Many of their players also have their own DACs, and for a lot of users will also double as desktop equipment – for our laptops, PCs, etc.
But the issue with this has often been twofold:
  1. Generally when we’re using home desktops set-ups, we’re also using full sized headphones, and sometimes we need a little more power than our portable devices can deliver
  2. The lack of adequate and easy to use volume control (at our finger tips) can be frustrating
So what would be the ideal solution in this sort of situation?  Perhaps a desktop dock which you can mate your existing player into, use the players interface or DAC, and the dock’s amplifier and other features.  We’ve seen this before with Fiios original E9 and E7 pairing – but never like this.
Welcome to Fiios new desktop amplifier / dock – the K5.  Or as Fiio likes to call it “an exclusive ride for Fiio players”.
In my time both owning and reviewing provided samples of many of Fiios products, I’ve often though how handy it would be to have a truly versatile docking system – and it has been something Fiio has been implementing quietly for a while now across their range (the use of the common 11 pin micro USB port).  So let’s have a look at how the K5 interacts with Fiios Xi, X3ii, X5ii and X7 players – and why I also think it is a winner with the E17K DAC/amp.
By now, most Head-Fi members should know about the Fiio Electronics Company.  If you don’t, here’s a very short summary.
Fiio was first founded in 2007.  Their first offerings were some extremely low cost portable amplifiers – which were sometimes critiqued by some seasoned Head-Fiers as being low budget “toys”.  But Fiio has spent a lot of time with the community here, and continued to listen to their potential buyers, adopt our ideas, and grow their product range.  Today, their range includes DAPs, portable amps, portable dac/amps, desktop dac/amps, earphones, cables and other accessories.
Fiio’s products have followed a very simple formula since 2007 – affordable, stylish, well built, functional, measuring well, and most importantly sounding good.

The K5 was provided to me gratis as a review sample.  I have made it clear to Fiio that I still regard any product they send me as their sole property and available for return any time at their request. But I thank them for the ability to continue use of the K5 – both for follow up comparisons and also for my own personal use.
I have continued to use K5 for follow up reviews, and I recently inquired if I could purchase the device from FiiO.  They have insisted I keep the K5 for my own use. So I acknowledge now that the K5 I have is supplied and gifted completely free of any charge or obligation.  I thank FiiO for their generosity. 

(This is to give any readers a baseline for interpreting the review).
I'm a 48 year old music lover.  I don't say audiophile – I just love my music.  Over the last couple of years, I have slowly changed from cheaper listening set-ups to my current set-up.  I vary my listening from portables (Fiio X5ii, X3ii, X7 and iPhone 5S) to my desk-top's set-up (PC > USB > iFi iDSD).  I also use a portable set-up at work – either X3ii/X7 > HP, or PC > E17K > HP.  My main full sized headphones at the time of writing are the Beyer T1, Sennheiser HD600, and AKG K553.  Most of my portable listening is done with IEMs, and lately it has mainly been with the Jays q-Jays, Alclair Curve2 and Adel U6. A full list of the gear I have owned (past and present is listed in my Head-Fi profile).
I have very eclectic music tastes listening to a variety from classical/opera and jazz, to grunge and general rock.   I listen to a lot of blues, jazz, folk music, classic rock, indie and alternative rock.  I am particularly fond of female vocals.  I generally tend toward cans that are relatively neutral/balanced, but I do have a fondness for clarity, and suspect I might have slight ‘treble-head’ preferences.  I am not treble sensitive (at all), and in the past have really enjoyed headphones like the K701, SR325i, and of course the T1 and DT880.
I have extensively tested myself (ABX) and I find aac256 or higher to be completely transparent.  I do use exclusively redbook 16/44.1 if space is not an issue.  All of my music is legally purchased (mostly CD – the rest FLAC purchased on-line).
I tend to be sceptical about audiophile ‘claims’, don’t generally believe in burn-in, have never heard a difference with different cables, and would rather test myself blind on perceived differences.  I am not a ‘golden eared listener’.  I suffer from mild tinnitus, and at 48, my hearing is less than perfect.
For the actual listening part of this review I used the K5 paired with all of the compatible Fiio products I have here, and and also compared it with my iDSD (my usual desktop DAC/amp).  This is a purely subjective review - my gear, my ears, and my experience.  Please take it all with a grain of salt - especially if it does not match your own experience.
  1. Volume matching was done with a calibrated SPL meter and test tones (1 kHz) when required for comparison.
  2. Other measurements were taken using a relatively cheap Startech USB soundcard, which I used primarily for recording THD on the headphone-out socket using loopback, as well as confirming the gain measurements. These measurements should be taken as an indication only, but at least show (in the case of the THD) that noise would be well below the threshold of audibility.
I thought I’d list (before I start with the review) what I would look for in a desktop DAC/amp. This is useful to remember when looking at my reasoning for scoring later in the review.
  1. Clean, neutral signature
  2. Easy to use
  3. Low output impedance – in case I want to use sensitive IEMs
  4. Reasonable output power – should be able to drive both IEMs and my full sized headphones
  5. Good gain control
  6. Good input and output options
  7. A variable line-out to connect my active speakers (and control from the device pot)
  8. Easy installation of DAC drivers and
  9. Value for money
  1. Desktop = Audio-gd NFB-12, Aune X1S, iFi Micro iDSD
  2. Portable = Fiio X3ii, X5ii, X7, E17K, Q1


The K5 arrived in Fiio’s retail box – a black retail carton measuring 150 x 195 x 60mm. The front had a picture of the K5 docked with the new X7, and the rear has specifications and other descriptive information in English and Chinese. The box is very smart – but some of the grey on black text is a little hard to read (better contrasting print colour would have been preferable).
K5 retail box front
K5 retail box rear
Opening the outer retail box reveals an inner box for accessories, and the K5 securely wrapped with a thin foam protective cover. The accessories include:
  1. An AC power adaptor and cord
  2. A USB data cable
  3. Some rubber stick on feet
  4. Small silicone spacer pads (for docking with smaller units such as X1 and E17K)
  5. 3.5 – 6.3mm adaptor
  6. Warranty and user guide
Inside the outer packaging
K5 and all accessoriers
The power cord and converter
The accessories cover pretty much anything you would need, apart from rear interconnects or rear connector cables – but those are usually user preference anyway.  The one cable missing which might have been handy would have been a USB mini to USB mini.
USB cord
Other accessories
The table below lists many of the relevant specifications for the K5.
Output Impedance H/O
<1 ohm
Max Output Power @ 16 ohm
>1.7 W
Max Output Power @ 32 ohm
>1.5 W
Max Output Power @ 300 ohm
>150 mW
>110 dB (AUX IN)
0.002% (1 kHz 32 ohm)
Frequency Response
20 Hz-20 kHz
0 dB / 6 dB / 12 dB
>70 dB (1 kHz)
Max Output Voltage
20 Vp-p
120 x 130 x 55mm
Outer Material
Titanium coloured brushed aluminium
Headphone Out
6.3 mm
Power Supply
For full specifications including detailed line-out and balanced out parameters, along with Fiio’s measurement graphs – follow this link
The K5 is rectangular shaped with rounded edges over the face, and a flat – but slightly recessed front and back plate.  The main body is titanium grey anodised aluminium with a nicely smoothed finish. The dimensions are pretty good for a small footprint amplifier (120x130x55mm).
Front face of the K5
Side view with dock tray up
Alternate side view
The front face is flat but nicely recessed, while still giving easy access to the controls. The most noticeable feature on the front face is the volume pot which has a diameter of 4cm and doubles as an on and off switch as well as the volume control.  When turned on, there is a deep blue LED which lights up around the volume knob – so you can easily tell if the unit is switched on.  I personally don’t find it too bright or distracting – it is actually rather soothing really. The tracking is super smooth and very easy to adjust.
On the left hand are two toggle switches – one to switch between the dock or line-in being active, and the second is 3 stage gain switch (low, med, high). To the right of the volume pot is the 6.3mm headphone jack.  It is reassuringly solid with a firm connection and feels very secure.
At the top of the unit is an ~ 67x 32mm hinged door, which when opened exposes the 11 pin micro USB dock.  The dock successfully mates with Fiios X1, X3ii, X5ii and X7 DAPS, and also the E17K DAC/amp).  I tried briefly to also mate the K1, Q1 and original X5 but none of these would fit.  None of the DAPs or DACs will fit the dock with cases intact either. As mentioned in the accessories, Fiio has included some rubber spacers for Fiios thinner devices (X1 and E17K) but I’ve found they fit well without using them. The dock itself has some forward and back play, and although it feels a little flimsy, seems quite secure once the connection between K5 and device is made. Sometimes I’ve had to wiggle a little to get the connection to align and slide in – but so far I’ve had no issues with actually making the connection, and it has remained stable.
Full rear panel
Balanced out and RCA port
Alternate dock input, USB-B connection and power input

At the rear of the unit is the input and output ports, and from left to right include:
  1. Dual 3.5mm balanced outputs
  2. A pair of RCA line-outs
  3. A pair of RCA line-ins
  4. A micro-USB line-in
  5. A standard USB-B digital input
  6. A DC 15V power input
I’ll go into more detail on the inputs and outputs later in the review.
I also tried to get some internal shots of the K5, but it’s a testament to how well the K5 is put together that the photos below are as far as I got.  There is a locking mechanism in front that I could have probably popped to remove the boards, but as the K5 is a loaner kindly supplied by Fiio, I didn’t want to push it.  What I will say is that the fit and finish of the interior matched the exterior.  The K5 internals are extremely tidy, and extremely well ordered – testament to the care that I’ve seen Fiio take with all of their products.
Dock internals exposed
Close up of the caps on the man board
Internals from the rear - really tidy!

For internal components, the K5 uses TI’s TPA6120A2 headphone amplifier chipset, which I researched and found that it is an AB amplifier architecture capable of delivering high bandwidth and power output with extremely low noise (up to 128 dB SNR and THD of 112.5 dB).  Fiios specs show the entire circuit having 110 dB measured SNR and THD+N at less than 0.002% (1 kHz @ 32 ohm), so the K5 is a very quiet unit.
So far I’ve noticed no heat build-up at all with the K5.  Even after several hours (driving my HD600s), it’s still cool to touch.
Fiio rates the target headphone impedance in their literature as being suitable for 16-300 ohm, and I can confirm that with my HD600, and utilising the E17K docked, and playing Amber Rubarth’s album “Sections from the 17th Ward” (which is an extremely well recorded binaural album which is normally quieter than my mainstream recordings), on medium gain with the pot at 12 o’clock I was consistently achieving an easy to listen to 70-75 dB range (measured with my SPL meter).  Switching to some well recorded rock (Dire Straits), and pushing the gain to high, and the volume to max, the HD600 sounded like speakers (I wasn’t wearing them at this stage), and the SPL meter was showing 95-100 dB.  Power?  Yes – plenty of it.
Next I switched to the 600 ohm T1, and again a really good performance from the K1.  The T1 sounded (subjectively) pretty well driven.  Comparing side-by-side with the iDSD and using the X3ii for input into both units, there really isn’t much noticeable difference at all.  The X5 might be marginally brighter – but we’re talking small margins here. And the T1 has about the same headroom as the Hd600.  Again – impressive.
So the K5 has plenty of power – what about some finesse? For the next test I used the very sensitive (8 ohm, 102 dB sensitivity) DUNU DN2000J.  Now I had the K5 on low gain and the pot at around 9am for a comfortable listening level.  There was still enough play to go lower still, and no signs of channel imbalance.
Verdict – the K5 is extremely versatile and will power a wide range of headphones and/or IEMs.
As I said earlier, I was able to test the K5 dock with a variety of Fiio DAPs and also the E17K. There are some pretty nice things they’ve integrated.  First up, if the DAC is enabled, the device will immediately enter DAC mode, the sample and bit-rate will show on the device screen.  It’s pretty seamless really. The issue you will have though (if you have multiple Fiio devices all using the TUSB DAC driver) is that the latest version of the driver uninstalls the old one – so for now it is impossible to have the X7 exist as DAC alongside the X3ii or X5ii.  It’s all a bit messy.  The good news is that the devices like the E17K use the windows default DAC driver, so it will still work OK. I’m not sure how many people will have multiple Fiio DAPs, and I’d bet that most would use only one device as DAC – but it is something to note anyway.
In USB storage mode, the X3ii and X5ii automatically connect to the PC if both they and the K5 are powered. They are automatically also charged (this happens whether the K5 is on or not).  The X7 in USB mode asks on screen if you want to connect the USB (when it is docked)
X1 on the dock an recognised
Integration is great with the device recognising it is docked

If the device (X3ii and X5ii) is docked and the K5 is off (but still connected to the PC), you still get access to the drives.  Turning the K5 on brings a message on the device screen telling you the device is docked,
Finally – if you turn the K5 off while the device is still docked, the device recognises this, and will power down automatically within 10 seconds unless you touch an input button to stop it.  The actual integration with the dock is pretty slick.
Connected to PC and hard drives available
On power down from K5, device will automatically turn off.
And the last thing you can do with the dock is simply use the device as a player, sending an analogue signal to the amp.  This makes it ideal as a small room or bedroom unit – where you don’t have need for use as a DAC.  This also brings the X1 into play with the K5 – as a player and amp only.
In the rear of the device are 3 inputs – the main USB input, the pair of RCA inputs, and the micro-USB “dock-in”. The USB in is straight forward – connects to your PC, and allows interaction between the dock and the computer.  The RCA inputs allow a line-in analogue signal into the amp, and I successfully used this with all of my other DAPs (L5 Pro, L&P5, X5 original) using a 3.5mm to dual RCA plug.  They worked successfully, and were very good in displaying how neutral and clean the K5’s amplification stage is.
The micro-USB “dock-in” is a bit puzzling though.  Fiio suggests it as an alternative way to connect the exact same devices that the dock uses (E17K, X1, X3ii, X5ii, X7) and the bit that has me stumped is why it is there at all. Logic would say you would use the dock. Unfortunately Fiio doesn’t supply a cable, and there is no cable supplied in the Fiio device accessories either.  I have a couple of micro to micro USB cables, but while I could get power, I could get no audio – so the pin-outs are obviously different. I guess it could be a good back-up if the dock ever breaks – but aside from that, and lacking a cable – it is a little pointless (to me anyway).
For outputs, there is a pair of balanced-outs (3.5mm), and I’m sorry I was unable to test these.  Then there is the RCA rear outputs – which are handy if you want to connect another amp, but unfortunately being fixed, they are useless for my primary use as speaker outputs to a pair of active monitors – which have no volume controls.  I hate using windows mixer to control the volume, and the idea of having the pot control the volume on the speakers would be perfect.  My iDSD does it and so does the NFB-12 (you can switch between fixed or variable on both).  The K5 (like the Aune X1S) only has fixed, therefore for me personally could never become my main amp for desktop use. And that is a real pity because it is practically perfect in every other sense.
I mentioned the gain earlier, and Fiio’s stated 0dB / +6dB / +12dB specification is spot-on (measured using loopback).  Like I said with the E17K, it’s pleasing to see a decent top end gain utilised which makes it quite practical. Gain does exactly what it says – simply raising the volume by a set amount. And the K5 has a suitably black background that raising the gain does not seem to be noticeably raising the noise floor until at very high volumes.  To check this, I used my wife’s super sensitive hearing (she can hear a cat walking on carpet from 10 meters away!).  I used the DN2000J again, set gain to low, and pushed the volume up until hiss was present – this was almost at the end of the pot (at least 80-90%).  On medium gain hiss was present at around 50% of the pot. On high gain it occurred at around 25-30%.  All of this was with no music playing, and utilising the extremely sensitive 8 ohm DN2000J. The reality is that if you’re using IEMs (and most won’t be with the K5), then on low gain you’ll have no issues, and you’d blow your brains out with volume before any hiss started.
Gain measurement
THD from the headphone out
With higher impedance headphones – it simply won’t be an issue. As a final test I also took the THD measurement for the Headphone out at - 3 dB on medium gain with a 1 kHz signal.  THD was actually much lower than Fiios stated % measurement, coming in at below 0.02%, and the total harmonic distortion + noise at below 0.07%. THD came in at .018%  and THD +N .069% - so it was clearly measuring the limits of my external sound card (cheap little thing it is) - still below the level of human audibility no matter which measurement you use.
I think I stated earlier that the K5 is essentially neutral – to me it is the way an amp should be – a window to the source. However I know people will want to read about individual pairings, so here is my very subjective take on the K5’s performance.
In the comparisons I used 4 tracks to get a feel for overall performance:
  1. Dire “Straits Sultans of Swing” for detail and overall tonality
  2. Amber Rubarth’s “Tundra” for soundstage and imaging
  3. Amy Winehouse’s “You Know I’m No Good” for bass performance
  4. Pearl Jam’s “Elderly Woman Behind The Counter In a Small Town” for vocal performance and tonality
I used IEMs for the X1 comparison – due to power limitations, and the HD600 for everything else. To compare apples with apples, I used the player mode – with K5 as amp, and also volume matched everything with an SPL meter.  Comparisons were sighted. 
K5 + X1 vs X1 (using q-Jays)
To be fair, this is the test that subjectively I saw no improvement on at all. The q-Jays don’t need the extra amping (despite being 50 ohm / 103 dB). On every test I ran the sonic qualities were to all intents and purposes identical – and this for me is a good things.  It shows the neutrality of the K5. The big benefit continues to be the ability to charge while docked, the access to the storage, and of course (when playing) the analogue volume pot’s ease of use.
X1 with K5
X3ii with K5
X5ii with K5 - ready to go in DAC mode

K5 + X3ii vs X3ii
I’ve always quite liked the X3ii and HD600 – I need to be at the upper end of the volume to get the best out of it (around 80/120 with a track like Dire Straits, and up to 100 for some of my more dynamic classical tracks). But I’ve often wondered about the mystical “being driven to its potential”. With the K5 there is a slight difference. The X3ii is very slight more “in your face” vivid and a little peakier. The K5 brings just a little more balance through the upper mid-range, and the bass is very slightly stronger – but overall it sounds just a little more relaxed in presentation (almost effortless).  Again we are not talking big changes – they are small – and I don’t think this is a form of colouration, but maybe of more power available to the HD600.  Imaging is similar, and if anything I would say that the slightly more relaxed “apparent” tonality of the K5 makes things appear a little wider.  Vocal presentation overall is too close to call – but I am amazed with both devices how well they can convey sheer musicality.  Detail in the Pearl Jam track is incredible with both devices.
K5 + X5ii vs X5ii
This time the two are a lot closer, and again the main (but extremely minor difference) coming through is the sense of relaxation in the presentation.  I actually had to recheck my SPL calibration to make sure I wasn’t hearing anything that wasn’t matched. The bottom line here is that the K5 will bring you a lot of extra headroom, but this time it really is providing a very transparent window to the source.  Details, vocal presentation, imaging are all really similar, and this reminds me again how well the X5ii is able to drive the HD600 on its own. Longer term listening and then switching still gives a sense of a slightly more relaxed overall presentation with the K5 – which is a lot harder to discern with quick AB switching. Both devices are a pleasure to listen to – but for desktop use I would again go with the K5 simply for the analogue pot and additional headroom.
X7 in DAC mode
X7 playing via the dock
Dialogue asking for USB data connection

K5 + X7 vs X7
I only have the AM1 (low power amp) for use with the X7 at the moment, and this comparison shows the effect of power with a headphone like the HD600.  The X7 will put 10 mW into 300 ohm, while the K5 is able to output 150 mW into the same load. The X7 can definitely get the HD600 loud enough, but like the other DAPs, there is not a lot of headroom. This time the same characteristics show though.  The K5 sounds more relaxed, and similar to the X3ii comparison. Tonally it is a little more balanced where the X7 (with the low powered amp) can get a little peaky (around the 4 kHz where we know there is a spike). I do want to make something clear though – I really like the X7 with the HD600 by itself – I think it sounds incredible. But comparing side-by-side with the K5, and the additional power is noticeable.  If you are an X7 owner, and you intend to use it also as a DAC (for PC/laptop use), I really would recommend considering the K5 as there are sonic improvements available with this combo.
I’m not going to go over old ground here – as you’ll already know from the above what improvements there are with the increased power of the K5. And the K5 is essentially window to what you’re feeding it – so there is no point going over sonics.  For this section I’m really looking at performance as far as latency goes – for gaming, video watching etc.
I’m using my PC which is home built – and has a Core i5-4690K (slight overclock to 4 GHz), an Nvidia GTX 960, and 16 Gb of onboard RAM.  I’m running Windows 10 64bit.
With the X7 and simply playing music, you’re not going to notice any difference or lagging – simply because you won’t have the visual clues. And BTW – the combo sounds really good using the X7 as DAC and the K5 as amp.  As good as my iDSD in fact (subjective).
X5ii in DAC mode and able to access DAC menu
These two were made for each other - E17K and K5
When I queued up a YouTube video, there was dramatic latency of at least a full second with the current driver set-up. I set the buffer settings for minimum latency and while it helped, they were still out. Playing a video with VLC needed around 0.4s synchronisation adjustment. Gaming is the same – with current drivers it is impossible.
Both the X3ii and X5ii show no really noticeable streaming latency with YouTube – even with the buffer set as “extra safe” in the TUSB control panel. With a movie from the PC there is no real latency either – perhaps a micro second or two, but not enough to make me immediately start searching for ways to correct it.
With the E17K there is no lag (at all), and this makes it a perfect companion for gaming, for video, for everything. So I’ll add its own section – because it deserves one - below.
E17K + K5
Purely my own personal opinion, and highly subjective – but the E17K for me is the ideal companion.  During the day I use it with my X3ii (for reviewing or for general listening).  At night I can simply pop it in the K5 (permanently set to 32 bit 48 kHz), and forget it’s there – as it charges, and handles the DAC duties without a hitch. For gaming, I pair it with Darin Fong’s OOYH surround software (highly recommended if you are a gamer or movie watcher – massively immersive). The best thing is that it doesn’t need drivers – it just uses a high-res driver inbuilt into Windows – so I tend to find I have less clashes with other software (personally I find the TUSB Fiio drivers for X3ii, X5ii and X7 clash with my iDSD driver from time to time – often the iDSD driver simply won’t load with the other enabled).  The E17K though lives happily with all my devices, never complains, or glitches.  It is rock solid.  Yes it is limited to 32/96 – but that is more than enough for my personal needs.
In side by side testing with the iDSD, they sound comparable to one another – I wouldn’t give either the edge on sonics (when paired with the K5).  The difference is in the iDSD’s ultimate power, portability and gain settings (and I guess the format support – need for testing/reviewing).  And the big one for me – the variable line-out to powered speakers controlled by the pot.  It is the K5’s one huge weakness.  If it had a switchable variable line-out, I’d be tempted to use it for my day to day private listening.
The only area I haven’t really covered so far is use of the K5 simply as a dock and using the line-out to another amp.  For this I used both my Little Dot MKIV and also the VE Enterprise (both OTL tube amps I will be reviewing at a later stage).  I own the Little Dot, and have the Enterprise as a loaner.  Both are simply fantastic amps, quite linear for tube based amps, and both brilliant with high impedance cans.
E17K + K5 to LD MKIV to HD600
E17K + K5 conencted to the VE Enterprise
This combo is really special

Once again with both combos, I’m hearing simply the sound characteristics of either the Little Dot or the Enterprise. And again it leaves me with the feeling that the K5 is an implementation done right. The K5 in particular is spectacular paired with the Enterprise – it really allows the overall dynamics and tonality of the Enterprise to shine through.


I’ve been through the entire review and haven’t once mentioned cost, so now is probably an appropriate time.  The Fiio K5 is currently listed on Amazon at approx. USD 110.00, and for that price, considering its versatility, you are getting one heck of an amplifier.
The K5 is built really well, has a reasonably compact footprint for desktop use, and has a good variety of input and output options.
Sonically it is very transparent, with low noise and reasonably high output – ideal for headphones up to 300 ohms, and certainly capable of driving even higher impedance loads.
But where the K5 shines is in its interactivity with other Fiio devices – specifically the X1, X3ii, X5ii, X7 and E17K. One caveat I would have is if you plan to use it docked with the X7 as a DAC for your computer – as there is high latency currently with video. You can’t penalise the K5 for this however, as it really is the X7 DAC driver with the issues.
The main problem the K5 has (IMO) is the lack of a switchable variable rear RCA out – which means at present you cannot use the volume pot to control powered speakers.  For me it is a bit of a deal breaker stopping the K5 becoming my default DAC/amp solution, but for others this may not be an issue.
In my opinion, the K5 will definitely suit anyone who:
  1. owns any of the supported Fiio DAPs or DAC/amps
  2. is looking for a desktop solution in tandem with an existing portable solution
  3. or is looking for a bedroom or second room set-up to give ability to pair a Fiio DAP with higher impedance headphones.
The K5 may not suit anyone who:
  1. does not own or intend to own other Fiio products
  2. does not intend to drive higher impedance cans
  3. requires a variable output to drive (active) speakers
As always, it is difficult to score an amp which is so good in so many areas, but has one glaring fault (see my original list). If this was a $200 amp I’d be tempted to give the K5 a 4.0 ranking, but when you take into account the very cheap price, the value proposition easily propels it to 4.5.
My thanks once again to Sunny at Fiio for allowing me to write my thoughts about the K5.
Thank you for your response, which one do you recommend me since you have experience for both of them? Portability is not a case here, only home. And my full-sized headphone is AKG K612. I think all of those amps can ''kill'' my K612 but which one you recommend? I feel closer to K5 since it seems really good for home.
+for my X3ii also (docking)
If you're using for home, and also with the X3ii as DAC - then the K5 is the one to go for.  For your intended use it will be pretty much perfect :)


twister6 Reviews
Headphoneus Supremus
Pros: accommodates docked X1/X3ii/X5ii/X7/E17k, Line In for other DAPs, USB In to use as USB DAC (w/docked DAPs), powerful output, soundstage expansion.
Cons: light on accessories (cables), uses generic external power converter rather than a more robust internal solution, can only dock DAPs without case/skin

I would like to Thank FiiO for providing me with a review sample in exchange for my honest opinion.
Manufacturer website:, available now from Amazon (noticed it back in stock) and B&H Photo/Video (should be in stock soon).
* Click pictures to expand.

Can you refer to a docking desktop amp as “jack of all trades”?  You certainly can when you start playing with FiiO’s latest K5.  Prior to receiving it, I was expecting K5 to be a desktop accessory for X7 only.  But was I wrong!  In addition to being compatible with FiiO’s latest X-series DAPs (X1/X3ii/X5ii/X7) and their E17k DAC/amp, it can also work with other audio sources connected to RCA Input, and even take advantage of DAC processing inside of a docked DAP while feeding audio from your laptop.  After spending over a month with it, here is what I found.
Unboxing & Accessories.
Arrived in a sturdy cardboard packaging box, I like how FiiO choose to have an all black background with a glossy image of K5 and a docked X7 popping out in “3D” from the front cover.  All the promotional pictures of K5 I’ve seen featured X7, but make no mistake – it’s intended to work with other FiiO X-series DAPs.  The back of the box has a detailed spec, including a very impressive output power rating for such a compact desktop amp.
Before opening the box, I did take a notice of the weight since we are dealing with an amp, though later turned out that part of it was contributed by external power converter.  Once taken out, you can feel that the actual amp is not that heavy at 450g, packed into 120mm x 130mm x 55mm compact enclosure.  The power supply converter is external, a typical AC/DC supply with 15V/1.5A output you can find with a number of laptops.  As a matter of fact, my review unit arrived with non-US plug and FiiO kindly included an adapter which got temporary misplaced, so I ended up using power converter from my old Thinkpad.
Other included accessories were 4 rubber bumps/feet, 2 insert adapters for different DAPs, usb cable (full size usb-B to usb), 1/4” headphone adapter, and a user guide.  Considering a number of all the inputs and outputs, it would have been nice to see other cables included with accessories, for example a pair of RCA to 3.5mm cables or 11pin micro usb connector, and maybe balanced 3.5mm cables.  Of course, these extra cables are not a showstopper to get you going, but still would have been great to see at least FiiO’s proprietary 11pin micro-usb interconnect cable.  The docking can only accommodate X-series DAPs without a case/skin, and you need to use this extension cable connected to “dock in” micro-usb port on the back of K5 if you want to keep your DAP dressed.
fiio_k5-02_zpszfjsvft0.jpg fiio_k5-03_zpsy1hdca7j.jpg
fiio_k5-04_zpsbkmo3phy.jpg fiio_k5-05_zpsbjiqlm1t.jpg
fiio_k5-06_zpswh0lf8jx.jpg fiio_k5-07_zpsbgkogxia.jpg
Since I’m into portable audio gear, I rely mostly on standalone DAP use, though have one desktop amp and a handful of portable amps.  In my opinion, K5 design fits somewhere in the middle.  It’s obviously a docking amp designed for a desktop use, but it doesn’t weight a ton especially since power supply is external to the case.  It’s lightweight, but still has a solid build with a nice titanium color aluminum shell.  It has a relatively small footprint that not going to occupy too much space, and yet it is sturdy enough on a flat surface.  As a matter of fact, I dragged it next to me on a couch and had no problem using it even so the surface wasn’t perfectly flat.  Ergonomics of the design and tight fitment and placement of the micro-usb connector contributes to a nice weight distribution without anything tipping over, even with X7 docked.
With K5 being a “docking” amp, the key feature of this amp is micro-usb docking port on the top under the flip panel.  When not in use or using external ports, the panel is flush with a top surface with an exception of a small tab to open it up.  The flip panel mechanism is smooth and the panel turns into a solid back support of a docked device when flipped open.  Inside you can see a pocket to cover micro-usb connector when it’s closed and another elongated pocket for a rubber adapter to accommodate different DAPs, depending on thickness variation.
The main focus of the front panel is a large rotary volume knob that also functions as a power switch once you turn it clockwise, greeting you with a brief red backlight glow while it initializing and then turning blue.  I absolutely love this detail which matches X7 blue light for a visual feedback when power is on.  Turning the power on will also turn the power on X1, X3ii, X5ii, X7, and E17k, and the same when you turn it off, though you can dismiss power-off from the DAP screen.  And with power on, your DAPs will also be charging.  The knob is big, yet easy to grip, has a perfect potentiometer resistance for a better control of the adjustment, and a clear white marker indicating rotary position which goes from -90 dB to 0 dB.
The front panel (the same as a back panel) is slightly recessed with a nice bezel trim design, and you can find to the left of the knob Input switch for Dock vs Line selection and Gain switch for Low (0 dB), Mid (6 dB), and High (12 dB) gain setting.  Input switch will correspond to a source selection of either DAP from the dock (or micro-usb “dock in” port) or the Line input.  In High Gain you can drive your HO output with a VERY impressive 1.5W (32 ohm load) power which scales down to 150mW (300 ohm load), and most likely with enough juice to drive your 600 ohm cans.  I found these flip switches have a nice click action.  To the right of the knob you will find 1/4" headphone output, keeping in mind that 3.5mm adapter was included with accessories.  I was happy to see FiiO didn’t clutter the area around HO with switches, keeping it clean.
The back panel of K5 reveals a Power in connector jack for 15V supply, all the way to the right, and a number of additional connection ports.  You have usb-B USB IN connector for digital input from your computer while processing a signal through X3ii, X5ii, X7, or E17K internal DAC, DOCK In input for 11pin usb interconnect cable if you can’t dock your DAP (due to case/skin), a pair of RCA Line In and Line Out connectors for external input connection from any audio source and to other audio source inputs, and Balanced Line Output.  This dual 3.5mm Balanced Line Out output can be used only in conjunction with X5ii or X7 to connect to another external amplifier stage.
fiio_k5-09_zpsxc7whxrk.jpg fiio_k5-10_zpsxujqfzuo.jpg
fiio_k5-11_zpskazbt1se.jpg fiio_k5-12_zpsp6a7j2ze.jpg
fiio_k5-13_zpshwrvudrc.jpg fiio_k5-14_zpsh99adr34.jpg
fiio_k5-15_zps8pt6weuv.jpg fiio_k5-16_zps6wl847qd.jpg
fiio_k5-17_zpsbrnjcg3e.jpg fiio_k5-18_zpsdy9ubcbv.jpg
Sound Analysis.
While testing K5, I focused on 3 main pair up scenarios with docked DAPs, external connection from LO of the DAP, and digital input from my laptop.  In every case I found K5 as an amp to be rather neutral, transparent, and contributing to a noticeable soundstage expansion (especially in width). 
Of course, pair up with X7 was at the top of my list.  By default, this flagship DAP from FiiO comes with IEM amp module which does a good job with in-ears and other efficient headphones, though I have to keep it in high gain.  K5 pair up really stepped up X7 performance with a deeper sub-bass, more organic mids, and additional sparkle in treble - a very consistent improvement I found across R70x (470 ohm) and both planar magnetic PM-3 and EL-8C.  Another change was in soundstage expansion, in all three dimensions of width/depth/height where width was the most noticeable.  I can't judge yet how other X7 amp modules going to compare, so keep in mind this is relative to IEM module.
docked icon appears in notification bar
fiio_k5-24_zpsisimobor.jpg fiio_k5-25_zpsunafv6vl.jpg
Docked with FiiO other DAPs, I found X3ii + K5 pair up to make sound more transparent, with a slightly improved dynamics and expanded soundstage, and with X5ii + K5 a found more body in lower mids giving sound a little smoother organic tone, and also the improvement in soundstage expansion.
Docked with X5ii
fiio_k5-20_zpsctha8nda.jpg fiio_k5-21_zpskkutislo.jpg
Docked with X3ii
fiio_k5-22_zps5z9hxw94.jpg fiio_k5-23_zpsumrar3yd.jpg
The docking convenience of FiiO DAPs is great, but K5 is not limited to only that and can be paired up with other DAPs.  Using a common RCA to 3.5mm cable you can feed Line Out of any DAP into Line In of K5.  I went straight to the top using PAW Gold as my guinea pig for this test, as well as AudioQuest Evergreen RCA to 3.5mm cable, and ended up with a big surprise.  Using Beyer's T5p 2nd gen, I found PAW Gold HO to sound nearly identical to PAW Gold LO + K5.  Sure, there could be a few subtle differences, but overall it sounded very close where K5 combo even had a slightly wider soundstage.
Last but not least, I put to the test my ThinkPad T430s driving USB In through DACs of the docked X3ii and X7 while monitoring through T5p 2nd gen.  This was really a proof of concept just to verify that both of the DAPs will be recognized by my laptop while docked, function as expected in USB DAC mode, and able to play FLAC files from Foobar2k on my computer.  Everything worked flawlessly, with a loud and clear sound improvement.  Pretty much anything would be a sound improvement over my laptop's HO from integrated motherboard sound chip.  But it also fared very well against a number of my other USB DACs, especially in conjunction with X7 DAC where sound became more dynamic, more detailed, and with a consistent improvement in soundstage width.
fiio_k5-27_zpsbieyg465.jpg fiio_k5-28_zpsvtctqbmb.jpg
something crashed on my laptop at the moment when I was taking a picture, thus X7 shows 0kHz/0bit, otherwise bit rate/depth displayed correctly during a normal playback
For sure you can call K5 a docking "jack of all trades" and "master of expanded dynamic sound".  This latest FiiO docking amp is quite versatile in boosting the performance of portable FiiO DAPs as well as any other DAP, and you can also use it connected to a computer/laptop as USB DAC powerhouse.  But among all of this it really shines with X7, replacing its IEM amp module with a more powerful alternative to take full advantage of ES9018S DAC performance.  In my opinion, K5 bridges the gap between X7 portable and desktop use where on the go you can enjoy your IEMs and efficient headphones, while at home you can supercharge X7 not only by "charging" it up when docked but also by giving it an extra jolt of output power.
Very informative review as always.
One quick question, have you tried docking the E17K? I would like to know what improvements or changes the K5 provides.
Thanks @twister6 :)
I just bought it, I've only one question , if I leave all the time my FiiO X3 2nd gen, what will happen to the battery ? Is the dock stop to recharge somehow? ty
I also just ordered this to use with my X3ii and HE400i. Curious about the X3 battery and whether this thing is powerful enough to get the most out of the HE400i?