[Listening test] Fosi Audio K7 - headphone amp & gaming DAC

Product: Fosi Audio K7 - headphone amp & DAC
Manufacturer: Fosi Audio - China
Cost: ∼€150 (right now on Kickstarter, until Feb 24, 2025)
Reviewed: Lucio Cadeddu - TNT-Audio Italy
Reviewed: January, 2025

Foreword

Headphones listening, due to common living needs (restrictions?), is becoming increasingly popular. The market offers many solutions in different price ranges, for example headphone amplifiers that also incorporate a D/A conversion section. This solution is convenient because it allows you to condense everything you need in a single device: connectivity of all sources and good driveability of different headphones. The K7 by Fosi Audio falls into this typology and replaces their old K5 model which was, actually, minimal and unambitious. From its rather unusual appearance, it is clear that this K7 wants to carve out a space of its own in the crowded global panorama of headphone amps.

A closer look

The Fosi Audio K7 is defined as a “gaming headphone amp & DAC” that is, a product designed not only for audiophiles but also for those into high-level gaming, which benefits from good quality audio. In fact, there is also a microphone input, with noise cancelling software, designed for online gaming sessions. For me, however, it is an interesting unit since it contains both a good headphone amp and a good DAC, combined with very good operational functionality. Indeed, there are 4 digital inputs: coaxial, optical, Bluetooth and USB-C (both UAC 1.0 and UAC 2.0, for high resolution audio), there is a volume control, bypassable treble and bass controls and two headphone outputs, a standard mini-jack 3.5mm unbalanced and a 4.4mm balanced jack. There is also an RCA line output to use the K7 as a simple DAC with adjustable output level, for example to manage active speakers or an external power amplifier. There are neither line inputs nor a remote control. A nice LCD display provides all the necessary information.

Technically, the DAC uses a very good chip, the AKM4493SEQ, capable of managing 384kHz-32bit/DSD256 PCM signals from USB and 24bit/192kHz from coaxial and optical. Via Bluetooth, however, you get only (...so to say) 24bit/48kHz lossless PCM thanks to a chip Qualcomm QCC3031, which supports aptX HD, aptX LL, aptX, AAC, and SBC.

The headphone amp section uses double chips OPA1612 and TPA6120A2, guaranteeing the driveability of headphones with an impedance between 16 and 300Ω. The output power on the unbalanced minijack is 600mW+600mW (32Ω/THD+N<1%) and rises to 2100mW+2100mW (32Ω/THD+N＜1%) on the balanced output. The gain of the amplification section is adjustable on two different levels: for the unbalanced minijack output +7.8dB (low gain) and +12.6dB (high gain) which become +13.8dB and +18.7dB on the balanced output. Power is provided by an external 12V 2A PSU unit. For other features, refer to the Fosi Audio official website, also complete with electrical measurements.

Versatile do-it-all

I tested the Fosi K7 mainly as a headphone amp, but also as a DAC. For a comparison, given the price class, I used the iFi Audio Zen Air Can, an excellent headphone amp of comparable price which, in our recent shoot-out test, had defeated the competition. Since the latter does not have a DAC section, the comparison would have been unequal had I used a better external DAC than the Fosi's internal one. Luckily the K7 has an analogue output, so the two headphone sections were powered by the same signal; that of the DAC inside the K7. The comparison, therefore, was absolutely on a par. Comparing the two amps was easy, since it was enough to move the headphones to one amp or the other, activating the analogue output of the K7 internal DAC, connected to the iFi Audio amp.

Since these are products of comparable cost, given that the K7 costs around €150 (which will probably become around €200 after the Kickstarter campaign) but has a DAC, and the iFi Audio costs 100€ and it doesn't contain a DAC, I didn't expect any striking differences. And so it was. In terms of driving, under normal conditions, both amplifiers were able to produce a very strong output, on all headphones used, of different sensitivity and impedance. In fact, their power output is comparable.

In broad terms I can say that the sound of the K7 is slightly more lively and spectacular, especially in the high range, while the iFi remains more controlled and, substantially, more linear. With certain recordings that tend to be soft and warm, the liveliness of the K7 could be beneficial, but in general I have almost always preferred the greater balance of the iFi. The latter seems to offer a deeper bass range, also with greater control and articulation. Not only that, but the correct scanning of musical tempos, especially in presence of demanding rhythmic textures, is slightly better. Likewise, I'd say that in presence of complex musical signals, regardless of volume, the K7 tends to sound a bit muddy, while the iFi glides by nimbly. With simpler musical programs, however, the greater liveliness of the K7 tends to be preferred.

The overall dynamics appear more natural and convincing with the iFi, although at the level of micro-dynamics, i.e. those small rapid variations of certain percussion instruments, the K7 performs slightly better. From the point of view of the 3D image, i.e. the sound being more or less spatialized “outside” the head, the iFi is better, while the K7 tends to concentrate the sound a little more inside the head . These are very small differences, and audible with headphones that cost 4-5 times these small amplifiers.

In summary, the comparison ends almost in a draw, with my slight personal preference for the iFi Zen Air Can. It should be considered, however, that the Fosi K7 also has a good DAC, capable of managing 4 different digital sources in high resolution (only three line inputs for the iFi), tone controls that can sometimes help and, why not, a definitely more refined and pleasant aesthetic.

Manufacturing & finish.
With €200 (or less) you take home a good quality DAC and an excellent headphone amp, so it's difficult to ask for more. Of course, a line input would have been welcomed (for example for a turntable equipped with a phono preamp), as would a remote control, given that in dim light the writing on the switches is absolutely illegible. The particular shape of the unit, very convenient for desktop use, may not be the best in an electronics rack, but this is not what it was designed for.
Sound.
Some traces of congestion with the most complex musical programmes reveal the overall inexpensive nature of the component. Even the chip used to amplify headphones, although used in other similar devices, does not have audiophile ambitions. I would have preferred a slightly more head-free sound. For me, who doesn't particularly like listening to headphones, this is a fairly important parameter.

Conclusions

After a couple of, let's say, questionable products such as the preamp P3 (the P4 will be released soon, in fact) and the ZA3 integrated amp, Fosi Audio seems to have taken a virtuous path, which began with the V3 amp, with the V3 Mono amps and with the ZD3 DAC, all very positively reviewed here on TNT-Audio. This K7, despite being designed as a “gaming headphone amp & DAC” is by all means a competent headphone amp combined with a good quality DAC. If you love listening to headphones, from any digital source, and don't disdain listening even with active and/or passive speakers combined with a power amplifier, this K7 can solve more than one problem, effectively behaving like the versatile heart of a modern system. Its quality/price ratio is, by all means, very high.

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