Closer Examination Continued

After all testing was completed, I set to disassembling the FiiO K9 Pro ESS to see what's inside. There were no stripped head screws this time around, so I was glad when the back panel came loose somewhat. However, the potentiometer pole of the volume knob on the front was not going to make it easy. I did take a few photos, but all they do is show the decent build assembly inside, so I excluded those photos here. The one issue I have here is the use of the plastic shield over the PCB which, while I understand is there for stability, can trap some heat inside unnecessarily.


Good thing then that FiiO came through with all the relevant information on the product page, which I verified as best as I could with the limited window I had—literally. No doubt the biggest thing of note is the dual flagship-class ESS Sabre Pro ES9038PRO digital-to-analog converter chips on this K9 Pro ESS model, replacing the single AK4499 used in the older K9 Pro presently discontinued while AKM sorts its production schedules out. There are two Texas Instruments OPA1612 low pass filters for these DACs, and the amplification stage is driven by two THX AAA 788+ linear amplifiers with FiiO justifying the absence of a THX AAA 888 by saying it would increase the BOM while requiring more heat dissipation engineering. Two Nisshinbo Micro Device NJU72315 volume ICs and a custom THAILIN/BingZi transformer take the maximum 33 W input from the AC mains (220 V and 0.15 A here) to 25 W fed to the electronics (15 V/1.664 A or 30 V/0.832 A). At this point, I noticed that my unit uses a green transformer while the photo above shows a brown one, but FiiO had anticipated this question I doubt anyone has asked before, and there's no practical difference between the two. We see the same XMOS U30881C10 USB encoder as on other recent FiiO DAC/amps, which is the commercial variant of the XMOS XUF208 32-bit microcontroller handling the USB input. Rounding off the primary components is a Qualcomm QCC5124 Bluetooth 5.0 audio SoC, which has recently been used successfully in several premium TWS earphones and Bluetooth headphones. Note that the PCB is partitioned to separate the power and audio signal sections from each other, with the analog signal loop on another separated section altogether to maintain signal integrity and get around any AC mains distortion.


Using the FiiO K9 Pro ESS is simple enough—you select the input and output of your choice and plug the wires in accordingly. The power cord is a given, and seen above are both the fitted out USB and Bluetooth digital inputs since I used those for all my testing. I did try the Type-C port on the side, but it's better left for mobile devices on a Type-C OTG connection. The side connection makes more sense if using the support stand with its silicone rubber base, which places the K9 Pro ESS at a vertical angle and saves desk space, too. However, as some of the side vents are covered, heat dissipation is worse in this configuration.


As with the FiiO K5 Pro ESS, we get an RGB ring with the volume knob. This multi-functional LED provides visual feedback on the operating state of the K9 Pro ESS, including sampling rate in USB mode, whether the output is muted, and even pairing and codec type when using Bluetooth input. Note the huge red text for a potential alarm state due to overheating or general abnormal behavior—FiiO clearly saw the dual ESS DAC implementation as a source of concern, which further explains why the THX AAA 888 amplifier chips weren't used. Regardless, once you sorted out the input and made sure everything is working as planned via the RGB LED, connect to and select your preferred output, be it the line out to active speakers or another amplifier or headphone out as with the HIFIMAN HE1000se paired to a custom Hapa Audio cable here (collective review coming soon). I appreciate the option of not only having full-size balanced XLR and SE 1/4" out, but a balanced 4.4 mm output, which is handy with portable earphones and headphones, too.


Before moving on, let me share some family photos of the FiiO K-series of products I have on hand, including the portable New K3 and desktop K5 Pro ESS we saw before. There is room for a FiiO K7 too, and perhaps even a larger K11 if FiiO decides step into the higher-end realm. But note how these three are segmented not only by physical size, but features in terms of I/O, in addition to others we can't see just yet. Logically, the K9 Pro ESS also costs the most of the three, but you already knew that.