Fosi Audio is a Chinese brand known for its affordable stereo amplifiers, pre-amplifiers, Monoblock amplifiers, and Bluetooth receivers, such as the
V3 Mono Monoblock Power Amp with
300W output and balanced input. Their stereo products are super popular in my country, especially in the DIY speaker scene. This brand is also quite popular globally for its affordable, high-price-to-performance ratio equipment.
Fosi has entered the portable game recently and has been quite successful so far. I have tried their
DS1 and
DS2 dongles, both of which provide excellent value for the money. SK02 is a bit different from typical dongles. I will not call it a complete desktop solution, either. Form factor and functionality-wise, it is close to the
Micca Origen DAC Amp, which has not been updated for years now, and I do not think we will see another Origen Amp.
There is hardly anything like the SK02 in the market, especially at such a tempting price point, and
I absolutely adore the SK02!
Disclaimer: I am an audiophile and a reviewer who works with Mr. @Sajid Amit of Amplify Audio Reviews. Amplify generally covers high-end IEMs, Accessories, DAC Amps, and Headphones, with occasional reviews of some budget products. Check out our video reviews at: https://www.youtube.com/@amplifyaudioreviews
Price:
$99 ($79 with coupons when applicable)
Specifications:
DAC Chip: ESS SABRE ES9038Q2M
Output Power:
3.5mm Single-End Output: Up to 280mW at 32 ohms.
4.4mm Balanced Output: Impressive 1100mW at 32 ohms.
Signal-to-Noise Ratio (SNR):
3.5mm Output: 120dB
4.4mm Balanced Output: 116dB
Noise Floor:
3.5mm Output: 13μV
4.4mm Balanced Output: 6μV
Supported Formats:
PCM: Up to 384kHz
DSD: Up to DSD256
Input/Output Interfaces:
3.5mm Single-End & 4.4mm Balanced Outputs, additional 3.5mm output on the rear
Supports both Optical & USB Inputs
Unboxing, Build Quality, and Features:
Fosi Audio SK02 arrives in a mid-sized cardboard packaging with Fosi Audio branding and slogan on the top side (
Hifi made fun). The only mention of SK02 is on the top right (
It is basically a small sticker with SK02 printed on it). Opening the cardboard box reveals the Fosi SK02 unit safely nestled in between foam cutouts, alongside a small manual and a long 1-meter USB cable. I actually liked the USB cable quite a bit. It is an OTG-supported Type C to C cable with an integrated Type C to USB A adapter on one end. I highly appreciate this adapter inclusion as it makes switching between ports and different devices seamless. The cable has some memory out of the box but it is above average overall in terms of quality.
The Entire Fosi SK02 outer shell is milled out of Aluminum. For a budget device, the powder-coated aluminum exterior feels extremely well made. There is no rattle or loose parts, and the connectors seem to be of very high quality. SK02 has three outputs. Primary outputs are the 3.5mm unbalanced and 4.4mm balanced port on the front. There is also an additional 3.5mm aux/optical output on the back. The rear output's power is still tied to the volume wheel, and SK02 can function as a Pre Amp via this output. The output power of this port is less compared to the front 3.5mm port. On the rear, there is a single USB port that handles data and power input simultaneously. SK02 also has a SPIDF optical port on the rear, which is an awesome inclusion. I can easily connect affordable streaming devices like the WiiM mini via this optical port whenever I want and turn the SK02 into a dedicated mini streamer.
I liked the multifunctional volume knob as well. It has really nice, tactile steps and micro-adjusting volume is a breeze. There is no sudden jump or drop in sound pressure level while adjusting the volume. The volume decrease/increase increments are highly linear and granular; therefore, finding the sweet spot is super convenient. Pressing the volume knob once pauses music; pressing it twice mutes the device and vice versa. Pressing the knob for a few seconds turns the device off or on.
SK02 relies on LED indicators to display the current status. There are separate LEDs for different bit rates, and the gain switch and input toggle switch have their own LED indicators as well. I loved how ingeniously Fosi audio has integrated volume level into a single LED. The volume indicator pulses with music beats, and depending on the volume level, the pulse rate increases exponentially, alongside subtle LED color changes (Purple to Blue and then to Red). Constantly lit volume LED without pulse means the SK02 has reached a very high volume. You might want to reduce the volume at this point to preserve your precious hearing.
Output Power and Sound Quality:
Though priced similarly to mid-fi dongles, SK02's output power is no joke despite being a single USB-powered device. The output power from the 4.4 mm port can reach up to 1100 MW @ 32 Ohms, which is in the same ballpark as serious portable devices like the
iFi Gryphon, Questyle CMA 18 Portable, and Shanling H7. The 3.5mm is also quite powerful
(280mW) if compared to dongles. 280 mW is where most dongles top out nowadays, that too on 4.4mm balanced out (understandable given the power efficiency and heat management dongles must maintain). There is a catch, though. Max power is only achievable when connected to a computer. SK02 works flawlessly with smartphones and tablets and remains quite powerful still, but as it is not as power-efficient as dongles, It will drain the source device's battery life at a much faster rate.
The SK02 effortlessly drives dynamic headphones up to 300 Ohms. I had no qualms driving the Sennheiser HD 650 on it, and the SK02 did a much better job driving the 650 than even flagship dongles
(Questyle M15 and Cayin RU7, for example). I also ran my Arya Organic at approximately fifty percent volume and enjoyed the synergy a lot! SK02 has a dead quiet output, so driving IEMs is a non-issue. I tried it with ultra-sensitive Campfire Ponderosa and FlipEars Aurora, and no trace of background hiss was to be heard. I have already praised the granular adjustment of the volume pot. No matter how sensitive or stubbornly hard to drive the IEM is, finding the sweet spot for each IEM has never been an issue.
Fosi Audio SK02 is a neutral-sounding DAC Amp with some extra warmth, though I will not classify it as a warm DAC Amp. I have never found the SK02 to be harsh or artificially boosted in the treble. I drive my Hifiman Arya Organic with it regularly, which is a significantly trebly headphone, especially in the upper treble frequency. I also drive my DITA Project M with it from time to time, which is known for its bright presence region. Neither of these two showcased any hint of extra harshness or treble sheen with the SK02. I actually find the SK02's treble to be more subdued than the Questyle M15 (artificial treble sheen) and the Earmen Angel (uses the same chip, significantly brighter in comparison).
The midrange performance is very decent. There is no recess or lower mid suck-out whatsoever. SK02 has a mildly warm-leaning, full-bodied, uncolored midrange that does nothing wrong fundamentally. SK02 showcased a very uniform, consistent performance across different IEMs and headphones in this frequency band. The vocals sound specifically good on it. In fact, I found the SK02's vocal rendition to be as good as the likes of Cayin RU7 and iBasso DC04 pro, if not better. Both of these two dongles cost more than the SK02, by the way. Guitar tones sound a wee bit soft, but that is only evident when A/B ing with much higher-end sources.
The low end is balanced and controlled, with no particular coloration or elevation in this frequency band. The bass sounds tight and properly extended with good subbass presence. Bass is also where Fosi SK02's budget underpinnings come into play. Compared to mid-fi sources like the Questyle CMA 18P, Mojo 2 and iFi Gryphon, SK02's low end is not as nuanced or textured. This comparison is unfair, though, as these three cost several times more than the SK02. Ironically, I prefer the SK02's bass to Cayin RU7's (too wooly and diffused for my taste). I would rate SK02's bass roughly at the level of iBasso DC04 pro and Colorfly CDA M1P.
Soundstage and imaging capabilities are decent, excellent, to be precise, and I have no qualms regarding SK02's resolution level. It is technically as sound as mid-high-level dongles. Moreover, SK02's exceptionally black background is a rarity, even among DAC Amps that are priced much higher. I was quite amazed when I paired the SK02 with the Aroma Audio A100TB portable combo. I understand it is a silly combo, given the A100TB costs $772, and what I was listening to was largely A100TB's own magic, but man, It genuinely sounded next level, even better than some high-end/mid-high-end portable device's raw output.
Comparison:
SK02 is a difficult device to compare due to its unusual yet practical form factor; I would still try to draw comparisons with a few portable sources, costing up to $300
Colorfly CDA M1P:
The CDA M1P is an underrated dongle that sounds awesome and provides great value for money. It is significantly warmer and denser-sounding and has a smaller soundstage than the SK02, which is less colored, has better dynamics, and is more spacious. M1P has better synergy with shrill/shouty IEMs due to its rounder, warmer top end.
iBasso DC04 Pro:
iBasso DC04 Pro is a neutral dongle and does not sound much different from the SK02. It has a slightly tighter and more textured bass response, but that is only evident when pairing both with high-end IEMs and headphones that have the capability to showcase these nuances in the first place.
Questyle M15:
M15 has a punchier, more robust-sounding low end, though I have some issues with its somewhat artificially boosted treble. M15 is more resolving than the SK02 (it is among the most resolving dongles, to be frank), but the soundstage is significantly smaller. I also prefer SK02's treble presentation.
iFi Hip DAC, ZEN Dac, Go link, and Uno:
I honestly see no reason to buy any of these over the SK02, especially the Uno and Zen DAC (as a standalone purchase), unless you are a hardcore iFi fan. The Go link is sonically inferior, but it is highly portable, so it is not a fair comparison. None of these four are particularly resolving or powerful. I am not too keen on the mythical
iFi timbre as well. they simply sound overly warm and low-res to me, especially in their budget segment.
