Closer Examination

The FiiO K9 is a desktop class DAC/headphone amplifier all-in-one device, akin to some others we have seen before. Indeed, it looks almost identical to the K9 Pro ESS to where it is clear FiiO has used the same chassis. It makes sense too since I quite liked that unit and the newer K9 is equally substantial at 200 x 225 x 72 mm while weighing ~2.66 kg—let's just say this thing isn't moving on its own. The chassis is composed of aluminium alloy but is smoother to the touch compared to the K9 Pro ESS and, more importantly in my books, is much cleaner without any gold accents anywhere. In fact, the front panel has also been improved to have far better visibility of the text to where I would personally take the K9 over the K9 Pro ESS if all other things were the same. We still have the slight cutouts and chamfers that FiiO has used in its K and KA series of DAC/amps recently to make the K9 fit into the design language of the brand. The front side has three headphone outputs in the form of a 4-pin XLR and 4.4 mm for balanced connections, as well as a single-ended 6.35 mm (1/4") out. In the middle is a large volume knob (analog pot with ADC sampling , 0.5 dB channel matching) with clear min/max and current level indicators marked. Then we get to more selections on the right including output type (headphones out, preamp, line out), gain (low/medium/high), input selector with the associated inputs at the top with LEDs, as well as a handy power/standby button for when you don't want to reach behind the back to physically power off the unit.


Such is the shift to a monochrome color scheme here that the top has all black and white branding too, including the two Hi-Res Audio logos as well as the THX logo. The FiiO logo above remains muted in color but we see the older logo being used here rather than the newer one. There are the same heat-dissipation vents on either side we saw on the K9 Pro ESS too, which could be a result of the power-hungry combination of DACs, the amplifier stages, and the integrated power supply. The FiiO K9 does not get the Type-C input on the side that was helpful on the K9 Pro ESS to connect to mobile devices though!


The back is filled with the same extensive I/O options that were present on the K9 Pro ESS. The internal power supply is on the left, as seen from the back, as opposed to the right in most other such sources. This means the left side has the AC power inlet with a dedicated power switch below, and the expected fuse between the two. The digital inputs are next and collectively marked as much, and now we see the Bluetooth antenna more clearly having been fixed on the device rather than a removable one. It does take away from the clean aesthetics, especially if you were not planning on using it, but I suspect most people will be happy to see this here rather than have two separate products in the form of K9 and K9 BT as with the FiiO K7. USB Type-B, optical, and coax complete this set before we move to the analog section when used with other devices in the chain. There are balanced 4.4 mm and singled-ended RCA line inputs to use the K9 as just an amplifier, as well as analog outputs in the form of RCA and dual 3-pin XLR to use the device purely as a DAC or preamp. On the back is confirmation that the FiiO K9 takes up a max of 30 W power as well as plenty of room to apply the rubber feet we saw in the box. A cutout here also provides access to select the operating voltage which should be already set to what your country uses out of the box.


After all testing was completed, I set to disassembling the FiiO K9 to see what's inside. As expected, the potentiometer pole of the volume knob on the front was not going to make it easy. I did take a few photos to show the decent build assembly inside but clearly it's not easy to see all the internal hardware. Note the use of a plastic shield over the PCB which, while I understand is there for stability, can trap some heat inside unnecessarily and once again is a remnant from the K9 Pro ESS design.


Thankfully FiiO comes to the rescue again in providing details about what makes the K9 tick, including the customized linear power supply section that incorporates four 4700 µF capacitors. The power supply section as well as the digital and analog sections are partitioned off from each other to avoid interference noise, with the two latter sections getting separate power too and having multiple low noise LDOs for voltage regulation. For most readers here planning to use the USB input, the XMOS XU208 USB controller is an older platform and I would have liked to see the newer XU316 instead—won't be a bottleneck to anything though! Bluetooth connectivity comes in the form of a Qualcomm QCC5124 Bluetooth 5.0 SoC to continue the theme of older hardware that still does the job. Differentiating the FiiO K9 from the K9 Pro ESS is the use of two less expensive ESS Sabre ES9068AS 32-bit 2-channel DACs compared to the dual ES9038PRO in the K9 Pro ESS, but once again I don't see any issues for the typical end user. There are two Texas Instruments OPA1612 low pass filters for these DACs and amplification comes courtesy two THX AAA 788+ linear amplifiers as well as two Nisshinbo Micro Device NJU72315 volume ICs. I will say that the volume pot used here isn't the smoothest in that I noticed the volume control with the knob has a dead zone early on, and then jumps in a more logarithmic manner rather than a smoother, more continuous approach even with analog inputs—this is down to the volume encoder and its implementation, perhaps FiiO could have gone with a different approach given this results in a reduced control range. All these provide excellent numbers for those prioritizing source measurements as seen on the front page and having been independently verified by others.