Closer Examination

The Fosi Audio K7 is a desktop class DAC and headphones amplifier, although it's not that much larger than some of the more imposing portable sources from the likes of xDuoo and FiiO. It measures in at 155 x 90 mm, with the height going from 32 mm at the front and 38 mm on the back. This makes it a very convenient device to place on your desk without taking too much room on it, and this also makes it more likely to find place for it closer to where you sit, since interacting with the buttons and knobs onboard is an ongoing process. That said, the Fosi K7 does not feel flimsy or cheap in any way thanks to its anodized aluminium chassis that weighs ~522 g for a solid feeling in the hands and on your desk. It only comes in black, albeit the use of white and orange accents help break away from monotony. There's a lot going on in the front and top, with two large knobs that rotate freely in either direction and are sat upon analog potentiometers—not the finest for volume control, but can be worked around with a good controller. These come knurled, making it easier to grip, and there is an accent mark in addition to position markers at the base to help you visualize the current position of the knob. The left knob is for volume control for the headphone outputs, and it also helps change the gain level as we will see later. The right knob is for microphone volume, in addition to help with the built-in bass and treble EQ functions. Between the two is a 1.5" LCD panel which the manual mistakenly refers to as using an OLED screen. This has orange symbols and letters come up to help with the built-in controls, and further branding is seen above.

Underneath the dials are a series of low profile buttons, some of which had more play horizontally than I'd like to see—certainly one of the things that helps distinguish a more affordable product from a more premium one, yet far from being a dealbreaker. From left to right, Fosi Audio provides a power button which doubles up to toggle through UAC 1.0 or 2.0 connectivity depending on what you are connecting to—some older consoles only work on UAC 1.0, for reference. Next are buttons to toggle through the various input and output modes, followed by a bypass button to, well, bypass any EQ settings on the device. The tone/mic button all the way to the right toggles through the three functions for the right knob—bass EQ, treble EQ, and microphone control—which you then customize using the knob itself. On the front, facing the user directly, we find a 3.5 mm TRS microphone input, a 3.5 mm TRS single-ended headphone output, and a 4.4 mm TRRRS balanced headphone output.


A look from the side shows the angled nature of the Fosi Audio K7, with the front being thinner than the back. This helps position the knobs and the display at a more approachable viewing angle for the user too. There are no vents to be seen here, so the hardware inside doesn't seem to necessitate active cooling. The max power input being 24 W from the external power supply, this is far from having a hot or power hungry Class A amplifier inside. The rest of the I/O is seen on the back, including a set of RCA outputs to bypass the amplifier and use with, say, an external amplifier or powered speakers. We also get a connector for the provided Bluetooth antenna to use for wireless Bluetooth input to the device, with coaxial, optical, and USB being the other input options. I appreciate that we get a USB Type-C input here rather than the larger, older USB Type-B ports we still see on many desktop DACs today. Finally, there's a 12 V barrel power input to use with the provided power supply itself.


The underside of the Fosi Audio K7 has one more of the thick anodized aluminium panels, similar to the one on the top, except this simply has four circular silicone rubber feet for minor vibration dampening, as well as to add friction against the resting surface and prevent any scratches to the metal chassis. These come with the brand logo applied on top too. After all testing was finished, I attempted to disassemble the device to get a better look at the internals. This began with simply pulling off the knob cover, showing one of those potentiometers we often see used in keyboards with volume knobs too—it works, but not the most precise volume control for a headphone amplifier. The bottom panel is held in place via four screws under the rubber feet, and it comes off easily enough to reveal the back of the PCB, with a thick thermal pad on the other side of where the amplifiers are probably located. Further disassembly necessitates more work, including potential de-soldering and removal of the hot glue copiously used on the internal screws. It's a good thing then that Fosi Audio shares more details on the hardware used in the K7, including an XMOS XU208 USB bridge, an older and less expensive part compared to, say, the X316, but one that should still work fine in minimizing any audio latency/skips. We see more component cost savings in the form of another older and less expensive DAC from AKM, the 32-bit AK4493SEQ stereo digital to analog converter that doesn't boast the best THD and SINAD numbers. Whether it matters in reality is a whole other matter, as the implementation of the DAC and other components ultimately is more important. This is associated with Texas Instruments OPA1612 low pass filters, with amplification coming via a pair of Texas Instruments TPA6120 op-amps. A Nisshinbo Micro Devices NJU72315 volume IC helps compensate for any channel mismatch with volume control from the potentiometer, with a Nisshinbo Micro Devices NJW1119A 3-band tone IC helping with the onboard EQ functionality.