Fiio K9 Pro review: squeeze your digital music

For a large part of the users, their relationship with digital music is based on connecting a headset to their mobile phone and opening Spotify or any other music platform. streaming to which they are subscribed. If this is your case and if you don’t aspire to much more, then perhaps the review of the new DAC / Amplifier FiiO, the K9 Pro, you probably won’t be too interested (or maybe you will… who knows?). However, other types of users have long been acquiring or downloading digital files of the highest quality (Bandcamp is for them a place they go to again and again), or they are subscribed to platforms of streaming like Qobuz, which offer files 24-Bit / 192kHz.

Of course, this type of user is the one who cares about having a decent sound system as well, in which the quality of the speakers or headphones they use plays a prominent role. However, there are not so many who worry about improving the reproduction process of these files, trusting “blindly” on the sound card of the computer or smartphone that they connect to their headphones or speakers. And yet it is in this process, of how the digital audio signal is converted to analog and therefore we can hear it, where much of the magic occurs. That is why, more and more, for the playback of music files, having a DAC has become an increasingly popular option.

What is a DAC and why are you interested in it?

The DAC (Digital to Analog Converter) is as its name suggests, the converter that “translates” the zeros and ones of digital music, into analog sound, which is what humans can listen to. This means that all the devices that you have in your house and that are capable of emitting sound, have their own DAC: your computer, your smartphone, your CD player … etc.

What is happening? That generally and with very few exceptions, the quality of the sound card integrated in computers and mobile phones is of very poor quality, so when playing a digital file, even if it is losless, much of the information is lost.

By having a dedicated DAC, however, the device correctly interprets all the information contained in the file and reproduces it with complete fidelity, which together with good speakers / headphones… a much improved sound experience is achieved. In many cases, connecting a DAC to our computer or smartphone is as big a change as having been used to watching VHS videotapes and suddenly starting to watch DVD movies.

That said, is a DAC an investment that makes sense for everyone? Let’s go back here to the beginning of the article. If music is something “accessory” for you or if you are not a big fan, probably not. Now, if you spend many hours a day listening to music and appreciate the quality and nuances … if you are passionate about music, then is an investment worth considering.

Fiio K9 pro

An all-terrain DAC with support for MQA

Once we have come this far and we have convinced ourselves that the DAC is a worthwhile investment, let’s see what it offers us FiiO and your new K9 Pro, a complete high-end DAC that also includes amplifier functions.

Designed to be used on a desk, the K9 Pro opts for an elegant design on a sober black anodized aluminum construction, and in which a large central volume wheel stands out above all the control elements. To its right, five LED indicators that inform us of the audio source that we are using (USB, optical, coaxial, RCA or Bluetooth); and under these four flat buttons (power on the equipment, source input, gain and the selector of the different modes -heads, amplifier and DAC-).

To the left of that big volume wheel, we find two balanced XLR headphone outputs of 4.4mm and 6.35mm unbalanced jack. This is joined on this front, a balanced 4-pin XLR port. What do we find on the back of this device? Basically, the input ports corresponding to these selectors that we talked about before (USB, optical, coaxial, and RCA), to which is added an RCA output connector and a 4.4 mm Jack connector. In other words: connectivity options are not lacking and in our case, being able to benefit not only from its functionality as a DAC, but also as an amplifier, what this K9 Pro offers has been enough for us to connect our PC, a CD player, a record player and a pair of external speakers.

Fiio K9 Pro review: squeeze your digital music 34

And of course this is important, but as you can imagine, almost all the magic of a DAC occurs inside it, so let’s see what we find in this case. In the first place, the Chinese company has opted to incorporate the chip AK4499 DAC from AKM Technologies. In this sense, we are talking about a high-end 32-bit chip, which supports the decoding of high-resolution audio signals with PCM decoding up to 32-bit / 768 kHz and native DSD512.

To give you an idea, a CD is usually recorded at 16 bits, most of the compressed audio files are encoded at 8 bits, while those that we find on platforms of streaming HD audio, they do it at 24 bits. On these same platforms, the digital music that we can download has a sampling frequency of 480 kHz. In other words, we will hardly find an audio file that cannot be decoded with the highest quality and natively, since these 32 bits are equivalent to what we will find in the recording master of most studios.

In addition to PCM decoding, the K9 Pro supports the new decoding MQA (Master Quality Authenticated), a very interesting technology since it allows an audio encoding that achieves small size files (up to one tenth of conventional Hi-Res) and can be reproduced reaching HD quality. It is not trivial, because to reproduce these types of files, we will precisely need an MQA-compatible equipment: although they are lossy files, the technology they incorporate share interpretation protocols that manage to restore the quality of the file that was initially encoded. In this sense, its approach is more akin to that of aptX technology for CD-quality Bluetooth sending than the infamous MP3 file.

Fiio K9 Pro

THX amplifiers for cleaner sound

In its work as an amplifier, the Fiio K9 Pro relies on modules THX AAA (Achromatic Audio Amplifier), that guarantee the power we need, while providing a clean sound.

In fact, this is the very goal of THX when designing this module: to provide an amplification system that increases the signal and volume with maximum transparency, that is, without added elements that “soften” the signal.

What we find, as the brand promises, is a good quality in sound amplification with very little distortion, without the need for intensive energy consumption, which favors its positioning in equipment contained in size, such as the new from FiiO. THX also points out that in its new model, it achieves a reduction of harmonic and crossover distortion up to 40 dB, which minimizes hearing fatigue.

A part to highlight of this equipment is that the DAC / amplifier function will change depending on the speakers to which we have connected the K9 Pro. In this sense, if the speakers are pre-amplified, we will have to choose whether we want to work with the DAC of exclusively (so we will not be able to use the volume wheel) or we choose the PRE option (pre-amplifier). Working in this case with a pre-amplifier will be useful if we have several devices connected to our equipment, since the signal that will reach the amplifier of our speakers (or even another amplifier that we may have) will be cleaner.

That this is a complete device is demonstrated by the fact that we can also play music through Bluetooth. However, and despite the fact that it is compatible with codecs such as AptX Adaptive / AAC / SBC, Bluetooth gives what it does and in this case, we will achieve a maximum transmission speed and bits of 96 Khz. Interesting as an “extra” but of course, no one would be willing to invest 800 euros in a computer, if what interests you the most is to be able to play music through this standard. That in addition in our tests we have experienced several micro-cuts here, does not help to recommend it for this particular point either.


The Fiio K9 Pro It is a team that plays in the upper-middle part of the market and it shows in all the details: starting with its construction, continuing with its connectivity options and ending with its commitment to cutting-edge technologies such as the chip AKM4499 DAC or THX AAA amplification modules.

If we also take into account that in the upper part of the market, these devices can reach 2,000 euros without too much effort, which Fiio offers a competitive quality for 800 euros it is certainly an element to value.

We cannot of course forget that it is still a device if not for audiophiles capable of spending thousands of euros on their equipment, yes for very demanding music fans and that in this case, thanks to the portability of the Fiio K9 Pro, they want to enjoy the best audio quality, for example when they are teleworking.

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Final assessment


The Fiio K9 Pro is a team that plays in the upper-middle part of the market and it shows in all the details: starting with its construction, continuing with its connectivity options and ending with its commitment to cutting-edge technologies such as the AKM4499 DAC chip or THX AAA amplification modules.

Audio quality and performance9

Build quality9

Installation / software8.5

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