FiiO K9 review: The Comprehensive Desktop HiFi Headphone Amplifier

FiiO K9 Pro has gained a good reputation for its rich interfaces, powerful power output of 2100mW (32Ω), and simple operating experience, but after all, the price of $800 is not affordable for all players. The launch of FiiO K9 is to fill the vacancy of the price below $500, and it is also a further addition to the desktop headphone amplifier product line.

FiiO K9 specs and features:

  • Bluetooth 5.1 with LDAC/aptX/aptX Adaptive codec
  • Dual-mode clock management
  • Dual-voltage linear transformer
  • THX AAA 788+ amplifier
  • $499 -Check latest price on AliExpress, Amazon US or other Amazon countries

Appearance, Interface and Configuration

As the low-end version of FiiO K9 Pro, the appearance design of FiiO K9 is naturally unchanged. The size, weight, shell material, and power supply method are basically the same, but the internal core configuration has widened the gap. For example, the audio DAC has been replaced by two ES9068AS from two ES9038PRO, and does not support MQA. In terms of the output performance of the amp, both the single-ended and balanced-ends have declined, and the peak output voltage and signal-to-noise ratio have also been slightly lowered.

In the interface part, the digital/analog input interface and single-ended/balanced headphone interface on FiiO K9 are consistent with FiiO K9 Pro. The number of interfaces is quite rich, the only difference is the lack of USB-C interface. This also means that FiiO K9 is still a little worse than K9 Pro in terms of playability with compatible USB-C interface devices. But don’t forget, the price of FiiO K9 is $590 (K9 Pro is $800), so for consumers, the choice still depends on your wallet.

In terms of parameters, FiiO K9 has reduced configuration in some places, but in fact, in terms of actual experience, the difference between K9 and K9 Pro is not very big. In other words, for most players, the gap in use experience is not very obvious. For example, all support USB, optical fiber, coaxial, bluetooth (compatible with AAC/SBC/aptX/aptX LL/aptX HD/LDAC/aptx adaptive). Both the analog input and the headphone output also support the same interface standard. Therefore, in my opinion, FiiO K9 can meet the needs of most users.

In addition, FiiO K9 is also equipped with the same fully balanced THX amplifier as K9 Pro – THX AAA 788+. It has both high dynamics and high power output, and has good details and dynamics when driving low-impedance and high-impedance headphones.

Headphone Matching and Sound Quality

In terms of headphone matching options, I have FiiO FH7S and HiFiMAN HE-R10 in my hand. FiiO FH7S is a hybrid five-unit earphones, which I usually use to listen to pop, rock and folk songs. HiFiMAN HE-R10 is usually used to listen to classical music, and HE-R10 is still relatively difficult to drive. In terms of hearing, I will have a chat with these two headphones. In addition, I still want to emphasize that the subjective consciousness of sound quality is too strong, and all hearing descriptions are for reference only.

The impedance of FiiO FH7S is only 18Ω, which is relatively easy to drive, but its five-unit acoustic structure cannot be driven by just any device. However, driven by FiiO K9, this earphone is still capable of controlling different music styles. It is more obvious that it can show a wide sound field and richer music details, and the sound quality can also be fully released.

According to the usual practice, listen to “渡口” first. What is more obvious in the sense of hearing is that the vertical sound field of FiiO FH7S is stretched, and the musical instruments and vocals have a good separation. In addition, the elasticity of the drum sound is very sensational, as if a real person is playing. In addition, FiiO K9 makes the overall atmosphere of FH7S better, and the lines of music are clearer.

Using FiiO K9 to drive HiFiMAN HE-R10, the excellent sound quality of the headphone itself has been well released, the sound bottom is very clean, and the energy sense of the sound has also been improved. Thanks to the good driving force of FiiO K9, HE-R10 can also control very well when listening to some large-scale classical music, showing a better sense of presence and atmosphere. At the same time, the depiction of music details is more clear and delicate.

In addition, if possible, I suggest you to listen to a few more headphones. You may find that the headphones that are originally dull or not well driven will become more dynamic and detailed when driven by FiiO K9. It can be said that among the current desktop headphone amplifiers within $600, FiiO K9 is one of the must-choices and has strong competitiveness.


Although it is a low-end version of FiiO K9 Pro, the actual experience of reducing the hardware configuration did not lead to a decline in its sound quality. The function is not much different from the K9 Pro, but the price is $210 cheaper. For those users who don’t need K9 Pro, the FiiO K9 is undoubtedly a more save money choice. Of course, there are actually cheaper options for beginner audiophiles – the FiiO K7 or FiiO K5 Pro.

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