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Review and Measurements of Fiio K5 Headphone Amp

amirm

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This is a review and detailed measurements of Fiio K5 headphone amplifier. I purchased this unit last fall and it has been sitting patiently for a review. The K5 costs USD $110 including free shipping from Amazon. What is unique about this product is that it has a dock mechanism to mate with the USB connector on Fiio portable audio players:

Fiio K5 Headphone Amplifier Review.jpg
By flipping the gray door on top of the unit different Fiio players can connect to it. You can then select that input with the front panel switch. In the back there is a USB jack that routes to the portable player, allowing it to be used as DAC. Without it, there is an analog-only amplifier with NO DAC built-in.

The case is metal but it has a paint on it that is normally is used to make cheap plastic look like metal. As such, it looks rather cheap to me. The volume control feels nice though. And it is fairly hefty so sits there without the cables pulling on it.

Power is provided by a laptop-sized 15 volt switching power supply delivering 1.5 amps from memory. So one would expect plenty of power to be available on tap.

There are a set of 3.5 mm jacks in the back that provided balanced output. I did not a 3.5mm to XLR cables so didn't bother testing that. And at any rate, that is more useful with their portable players.

Let's get into measurements and see how the K5 performs.

Measurements
My dashboard for headphone amps involves feeding 2 volts in, and getting 2 volts out ("unit gain"). The Fiio K5 conveniently has a "0 dB" low gain switch for this purpose:

Fiio K5 Headphone Amplifier Measurements.png


Distortion is limited by second harmonic at -108 dB or so. SINAD (signal over noise and distortion) is therefore shy of the 114 dB that its competitor, JDS Labs Atom produces. In other words, respectable but not top of the class.

I am not a fan of SNR measurements (as it ignores distortion) but you all want it so here it is: :)
Fiio K5 Headphone Amplifier Signal to Noise Measurements.png


This ranks well:
Fiio K5 Headphone Amplifier Signal to Noise Table Measurements.png


Frequency response is rule flat and excellent:
Fiio K5 Headphone Amplifier Frequency Measurements.png


Output impedance is likewise 1 ohm which is low enough for just about every headphone load:
Fiio K5 Headphone Amplifier output impedance Measurements.png


The most important measurements for headphone amplifiers is power versus distortion+noise. Here it is using 300 ohm load:
Fiio K5 Headphone Amplifier Power at 300 ohm Measurements.png


Noise level dominates the sloping down part of the curve and there, the K5 almost keeps up with the JDS Labs Atom. But then distortion starts to set in around 10 milliwatts and performance degrades some (gracefully). Importantly the power output is half of what the Atom produces. At 121 milliwatts though, it easily clears my requirement of more than 100 milliwatts to provide good power for high impedance headphones.

At low test impedance of 33 ohm we are measuring current delivery capability:

Fiio K5 Headphone Amplifier Power at 33 ohm Measurements.png


Here, the Fiio K5 becomes noisier than Atom and again, distorts more. Power output is similar though and very good at > 1 watt.

Intermodulation distortion versus output level (and hence power) repeats the same story:
Fiio K5 Headphone Amplifier IMD Measurements.png


Low and mid-gain again show somewhat more noise level than JDS Atom (dashed lines). High gain though was much worse. Not sure what went on there.

Channel matching is very good until you get down to low levels where it goes nuts:
Fiio K5 Headphone Amplifier Channel Imbalance Measurements.png


Given the 0 dB low gain setting, hopefully you don't have to operate it in that region much. FYI I changed the output level to relative dB so that you can tell the amount of attenuation (red) for every imbalance level (blue). Let me know if you like that better than previous graphs that showed the voltage instead.

Listening Tests
Throwing my bass heavy tracks at the Fiio K5 while driving my Sennheiser HD-650 high impedance headphones resulted in very satisfying sound and high levels of power. I could literally vibrate my ear lobes with it. :D Alas, while you have ample power at 12 to 1:00 o'clock, going beyond that I could hear the bass distortion in the amplifier prior to driver doing the same.

Similar story emerged with Hifiman HE400i low impedance headphone. Lots and lots of power, great dynamics, etc. until you pushed hard past 2:00 to 3:00 where bass distortion in.

Note that outside of testing, I would not need to go to the region where distortion was quite evident. So in practical use, there is plenty of distortion-free power available.

Conclusions
I can't find anything wrong with Fiio K5. The issue it has though is the impossible battleground created by the JDS Labs Atom with its combination of high power and extraordinary low distortion. Compared to that reference, the Fiio K5 falls behind one step or so.

I am happy to recommend the Fiio K5 if you need its dock capability or like its volume control, etc. Good job has been done here by Fiio.

This unit is available for sale if anyone is interested.

------------
As always, questions, comments, recommendations, etc. are welcome.

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graz_lag

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#2
Very nice review @amirm as usual.
Product very well engineered for its price, unfortunately it cannot keep up the comparison with the Atom as you said.
Chapeau to FiiO for the great job though.
 

flipflop

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#3
So it has a DAC but it can't be used at the same time as the amp? Would have been an absolute killer product in that case.
Any chance you're going to measure the DAC portion?
 

mindbomb

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#5
I like the new channel balance results being in decibels. Previously, I would bust out a calculator to do the conversion myself to make sense of the results.

One question is how fiio got the output impedance so low using the buffer they were using. Doesn't everyone else use 10 ohms with it?
 

trl

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#7
[...]

One question is how fiio got the output impedance so low using the buffer they were using. Doesn't everyone else use 10 ohms with it?
Hope it helps, but Russ White got an 10mH inductor in parallel with a 22Ohms resistor: http://www.twistedpearaudio.com/docs/linestages/ventus_ez_schematic.pdf, others found a different way to reduce output impedance without affecting the stability.

PA probably did something similar, otherwise couldn't achieve 3mOhms of output impedance: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?start=6.

L.E.: Actually I don't know how PA achieved that low output imepdance, maybe he simply connected the TPA6120A directly to the headphones jack after all: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?showall=1 and http://sjostromaudio.com/hifi_pics/hifi_100pr/qrv07r0_TPA6120.jpg might help, but I see that the two 10.2Ohms blue resistors are connected directly to the output pins and I guess from J1/J2 jumpers these resistors could be shorted. Also, on QRV09 the output impedance is 10/120Ohms: http://sjostromaudio.com/pages/index.php/hifi-projects/130-qrv09-headphone-amp?start=5
 
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#8
While having an amp you can dock one of their portable players in is an incredibly nice feature Fiio really needs to get on adopting USB-C across their entire lineup of products
 
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#9
The Atom is very hard competition indeed, but the K5 is still a respectable unit it, probably on par with the venerable Objective 2.

Amir, do you have the new Fiio K3 available?
 

graz_lag

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#10
While having an amp you can dock one of their portable players in is an incredibly nice feature Fiio really needs to get on adopting USB-C across their entire lineup of products
Being FiiO a satellite within the Oppo's solar system, for sure they have the resources and know-how to keep up with the market trends as far as the audio portable gear businesses are concerned.
 

graz_lag

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#11
@amirm : thank you for adjusting the shot's exposure, the face-plate details can be clearly identified now !
Why not posting a shot of the back / connections as well as a general rule in your reviews ?
Yeah we find everything on the Internet but a shot of yours on the back as well may give us additional nice information's such as the unit serial number for example ...
 
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Jimmy

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#13
In this thread from another forum there are high res internal pictures :

https://soundnews.ro/2016/03/13/fiio-k5-docking-power-2/

It seems they just used 1 ohm output resistors instead of the usual 10 ohm for the TPA6120, how they make it stable, I don't know, but other designs even allow bypassing the output resistors with jumpers at your own risk.

Maybe using a better power supply will help to improve performance, at least it does with the Monoprice Desktop Amp/Dac which is a more textbook TPA6120 design (almost a copy paste from TI's example application).


Hope it helps, but Russ White got an 10mH inductor in parallel with a 22Ohms resistor: http://www.twistedpearaudio.com/docs/linestages/ventus_ez_schematic.pdf, others found a different way to reduce output impedance without affecting the stability.

PA probably did something similar, otherwise couldn't achieve 3mOhms of output impedance: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?start=6.

L.E.: Actually I don't know how PA achieved that low output imepdance, maybe he simply connected the TPA6120A directly to the headphones jack after all: http://sjostromaudio.com/pages/index.php/hifi-projects/128-qrv07-headphone-amp?showall=1 and http://sjostromaudio.com/hifi_pics/hifi_100pr/qrv07r0_TPA6120.jpg might help, but I see that the two 10.2Ohms blue resistors are connected directly to the output pins and I guess from J1/J2 jumpers these resistors could be shorted. Also, on QRV09 the output impedance is 10/120Ohms: http://sjostromaudio.com/pages/index.php/hifi-projects/130-qrv09-headphone-amp?start=5
 
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amirm

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#16
Why not posting a shot of the back / connections as well as a general rule in your reviews ?
Besides laziness :), if I put another picture there, both show up on the home page making the snippet a lot longer. Maybe I can squeeze a small one there....
 

flipflop

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Besides laziness :), if I put another picture there, both show up on the home page making the snippet a lot longer. Maybe I can squeeze a small one there....
You could try spoilering it.
 

amirm

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You could try spoilering it.
Ah, I could also leave it as a thumbnail but not sure how the article system treats them. Thanks for the suggestion.
 
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Besides laziness :), if I put another picture there, both show up on the home page making the snippet a lot longer. Maybe I can squeeze a small one there....
Why not reserve the first reply and add additional media there?

Edit: this would also give you a great place to aggregate additional results from further testing you frequently do during the discussion!
 

amirm

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