Fosi Audio SK02

A huge thanks to @fosi_audio for providing me with the SK02 DAC for review purposes. However, my opinions remain unbiased and my own.
Testing Duration

• 15 Days

Tested With

• Simgot EM6L
• Simgot EW200
• HIDIZS MS-1
• TruthEar GATE

Specs:


What‘s In The Box？

• Fosi Audio SK2 x 1
• USB Type-C cable x 1
• Optical cable x 1
• User’s Manual x 1

Unboxing

Design, Build Quality & Input/Outputs

The SK02 has a really nice and honestly unique design for a desktop DAC, offering a super compact form that frees up space on your desk without compromising quality. The body, faceplate, and knob are made with a full aluminum construction, featuring a semi-matte black finish that feels incredibly premium in hand. The knob offers a consistent, smooth scroll, while the buttons provide a satisfying tactile bump.

On the faceplate, there’s a row of LED indicators on the left— the first set shows whether you’re in high or low gain mode. The next row indicates your PCM frequency, and on the top right, you'll see the input mode. Below that, another row lights up to indicate if DSD mode is enabled and what sample rate you're using.
Moving to the front, you’ll find two outputs: a 3.5mm and a 4.4mm. On the back, there's the power/USB-C input, optical input, and a 3.5mm input. The bottom has a nice set of rubberized feet that ensure the unit stays firmly in place on your desk.

Overall, I really appreciate the premium and sleek design that the SK02 offers. Combined with excellent build quality, I honestly can't find a single flaw—it feels incredibly well-built throughout.



Summaries

• Compact, premium aluminum design with smooth knob and tactile buttons.
• LED indicators for gain, PCM frequency, input mode, and DSD status.
• Multiple outputs and inputs with stable rubberized feet.

Knob

The knob has a smooth semi-matte finish, just like the rest of the body. While some knurling would have been a nice touch, there’s really nothing to complain about here. The knob has a smooth scroll with slightly defined notches, and honestly, it feels really good to use. Clicking the knob once works as a play/pause button, and holding it down acts as the power button for the SK02. Overall, I really like the premium feel of the knob, with the added functionality being a great bonus.

Summaries

• Smooth scroll with defined notches, doubles as play/pause and power button.
• Feels premium and adds great functionality.

Sound

When it comes to sound signature, the SK02 offers a fairly neutral tuning that leans slightly toward the warmer side. There’s no overly harsh emphasis on the treble or bass, allowing you to experience the true sound signature of the IEMs or headphones you connect to it. Personally, I don’t use headphones, so I can’t vouch for how well the SK02 performs with them. However, when it comes to IEMs, the SK02 offers more than enough power, leaving nothing to be desired.
Honestly, I’ve never heard my EM6L sound this good. Even when hooking up more affordable pairs like the GATE, they still sound way better—almost like they’re more expensive. This is thanks to the SK02’s ability to provide clean, clear sound without altering the tuning of the devices you connect, while offering plenty of power to drive any IEM out there.

Summaries

• Neutral, slightly warm tuning with clean sound.
• Drives IEMs well, making even budget models sound great.

Gaming


When it comes to gaming, I highly recommend the SK02. Thanks to its neutral tuning, there’s no emphasis on overly harsh sounds, allowing the tuning of your device to shine through. I found that the SK02 provides a really good and open soundstage in games, handling busy audio environments exceptionally well. You can clearly distinguish where a grenade is going off or where footsteps are coming from, even during chaotic gunfights with shots flying everywhere. There’s no muddiness in the sound, and overall it delivers a really clean and detailed audio experience, whether you’re playing esports titles or enjoying casual gaming.

Summaries

• Clear, open soundstage; handles busy audio perfectly.
• No muddiness, great for distinguishing in-game sounds.

Conclusion

In conclusion, I can wholeheartedly recommend the SK02 to anyone looking for a budget DAC, especially IEM users. I don’t see you needing anything more to drive your IEMs. It’s packed with features, offers outstanding build quality, and comes in a really compact size with a premium aesthetic that fits any setup. In actual use, the SK02 delivers amazing, clean audio in every situation and really stood out to me during gaming, providing crystal-clear audio cues. For the price—and even beyond—I can’t think of anything I’d recommend over the SK02. It’s simply an amazing device without a single flaw that I’ve found during my time with it, and it’s definitely going to be a staple on my desk moving forward.

Summaries

• Great budget DAC, especially for IEMs.
• Compact, feature-packed, and delivers clean, impressive audio.

Pros

• Great build quality
• Amazing looks
• 3.5mm and 4.4mm output options
• Quality feel on the knob and buttons
• Various input options
• Great power output
• Compact form factor
• Excellent price-to-performance

Cons

• Could have better-looking packaging, but that’s the only thing I can think of.

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Disclaimer:

• - Fosi Audio sent this unit to me in an exchange for an honest, unbiased review. Rest assured that this review will do its best to devoid from any bias/es as much as possible.
• - I have not tested this with MQA files or MQA streaming since I don’t use MQA at all.
• - The following remarks and observations shall be made and owned only by me.
• - No monetary compensation is/was involved before, during, and after the period of creation of this review.
• - I have only tested this with earbuds and IEMs only.
• - Your mileage may (and always, will) vary.

Burn-in time: 5-10 hours per day, 10 days.

IEMs/Earbuds/Source used:

• - Etymotic ER3SE
• - Sivga Que
• - Simgot EW300
• - Letshuoer S08
• - Tanchjim 4U
• - Kiwi Ears KE4
• - Kiwi Ears KE4
• - Temperament X6
• - Sony Xperia X Compact
• - Aiwa XP-V710C CD Player (12 sec. EASS)
• - Non-HiFi smartphone (Infinix Note 12 G96)
• - Desktop PC, Laptop.
• - Local Files via Foobar, YouTube Music, Deezer, and Qobuz with UAPP.

Setup configuration: Fosi Audio SK02 paired with phones/laptop/pc.

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Essential Product Specifications:

• - 3.5mm Output:
• - High Gain: 280mW @ 32Ω, 130mW @ 64Ω
• - Low Gain: 90mW @ 32Ω, 50mW @ 64Ω
• - 4.4mm Output:
• - High Gain: 1100mW @ 32Ω, 550mW @ 64Ω
• - Low Gain: 350mW @ 32Ω, 180mW @ 64Ω
• >Inputs: USB, Optical (OPT)
• >Outputs:
• - 3.5mm Headphone
• - 4.4mm Headphone
• - 3.5mm Line Out/OPT
• >Headphone Matching Impedance: 16-300Ω
• >PC-USB Sampling Rate: 32Bit/384kHz DSD256
• >OPT Sampling Rate: 24Bit/192kHz
• >DAC Chip: ES9038Q2M
• >Power Supply: 5V, USB Type-C

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Sound signature:

• Just like its smaller, older siblings, the Fosi Audio SK02 presents itself in a neutral, nearly transparent manner. This can be a good or a bad thing depending on the user’s preference and pairing, and it paired well with all of my IEMs and earbuds. The SK02 is not as transparent as what the Tanchjim Space exhibits, especially on the upper frequencies, but it isn’t a deal-breaker, or even noticeable on its own for me to hear.

Build Quality:

• Build quality is rigid, compact, and has a good amount of heft to it, for me to call it a desktop DAC instead of a “dongle”. I also believe that this is not meant or designed to be used as a dongle as well, due to its size and device compatibility (will be discussed later). Its size is also in and within the desktop DAC territory, along with the iFi Uno, or Topping DX1 in terms of size.There are the ports that you usually see in most desktop DACs as well, such as optical and out ports, aside from the usual 3.5 and 4.4mm ports.The SK02 is operated with two buttons, which are the gain and mode buttons. There are also plenty of LED indicators here as well which tells the file type being used, its bitrate, on and off, mode, and a “real time indicator). This desktop DAC is controlled with the use of its volume knob, that also acts as a play/pause/mute/unmute button when pressed. Its volume is also independent from the software volume and can be controlled precisely since it has a bit of soft “clicks” when turned. Overall, I do not have any problem nor encountered any problems when using the Fosi SK02. However, if I were to nitpick, it would be its volume knob, because I am used to volume knobs having a “tactile” volume limiter on both ends of the volume level, which this do not have.

Device Compatibility:

• I am unable to use the Fosi Audio SK02 on my phones due to its high power requirement. I have already anticipated this way before due to its specification, so I am not surprised that this happened on my end. Laptops and Desktop computers will connect with this USB DAC with no problems since this USB DAC is plug and play and does not have any bundled software with it. As for the tablets, It can be a hit or miss depending on the brand. Huawei tablets do not work with this USB DAC, while Samsung Tablets pair with this dongle with no problem. I haven’t tested this on iPads.

Battery Consumption:

• This desktop DAC requires more battery juice when compared to the usual USB DACs. It consumed around 50% of the battery of the Samsung tablet I have tested with after 3 hours of usage. This added to my conclusion that the Fosi Audio SK02 is designed to be used with desktops or laptops rather than being used as a portable dongle.

Power and volume:

• This is where the Fosi Audio SK02 shines - its power output. I had no problems pairing this with any IEMs and earbuds I have with me. Whether it be easy to drive or hard to drive planars, the Fosi Audio SK02 will handle it well, due to its two gain modes and precise, tactile volume knob. Here are the IEMs I have tested with this USB DAC and the volumes required for me to drive them properly:
  • Etymotic ER3SE - 10/100
  • Temperament X6 - 14/100
  • Letshuoer S08 - 12/100
  • Simgot EW300 - 8/100
  • Rose Technics Star City 5 Pro - 10/100
  • Tanchjim One - 20100
  • Kiwi Ears KE4 - 8/100
  • Sivga Que - 10/100

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Pros:

• One of the “most powerful” USB DACs under 100 USD in terms of power output! (as of today)
• All-rounder “neutral” sound with nearly zero coloration!
• Pitch-black background!
• 3.5mm and 4.4mm ports!
• Can be used in optical mode.
• LED indicators!
• Two levels of gain!
• DSD256 support!
• Tactile, dual-function volume knob!
• Durable, premium feel and design!
• Plug and play!

Cons:

• Will not work on some phones/tablets due to its high-power requirement/demand.
• Volume knob does not have a tactile/physical limit on both extremes of volume level.
• No bundled application/EQ software (not really a con but I have to point it out apparently)
• Meant for desktop/semi-desktop use as it demands more power than most DACs (not really a con but I have to point it out)

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Fosi SK02 Review: THE BEST UNDER $100​

WATCH FULL REVIEW HERE:​

PROS​

• One of the best desktop sources under $100
• Very high power output for the price
• 4.4mm Balanced Output for sub $100 desktop amp
• 1100mW on 4.4mm balanced
• Clean, neutral tone with no coloration
• Improves transients and dynamics drastically
• Immersive headstage and imaging performance
• Perfect headroom for most gear
• Solid build quality
• Very informative LED presentation
• Solid features
• Interesting form factor
• High quality interface
• Intuitive layout

CONS​

• Phone compatibility
• No RCA input
• Non-traditional shape (nitpick)

WHO THIS UNIT IS FOR​

• Anyone looking for a good quality desktop source
• People looking for a powerful, clean but affordable source
• People looking for neutral source that improves the best parts of your headphones
• People looking for a feature-rich source
• People looking for the best value source in the market

WHO THIS UNIT ISN’T FOR​

• People who want a portable source
• People who want a more colored source
• People who want a source with better phone compatibility
• People who want a more traditionally shaped source

SHORT REVIEW:
I cannot think of any major cons with the SK02 that bars it from being arguably the best desktop source to get in 2024. Insanely high output, rich features and a superb sound that enhances everything I plug into it with enough power to drive anything. Maybe you’ll take issue with its compatibility, the shape or the lack of RCA, but as someone who’s been searching for the one source I can use to not only review but listen to music, the SK02 lived up to my expectations and more. HIGHLY RECOMMENDED

FULL REVIEW


In the world of portable dongle DACs littering the market, it’s hard for desktop jockey's like myself to find a reliable all-in-one device to power everything that I have with enough driving force and a clean output at a reasonable price.

That was until Fosi came along and released the Fosi SK02. But what exactly makes the Fosi SK02 the best budget desktop DAC/AMP in the market today?

DISCLAIMER:
Big thanks to Fosi for sending over the SK02 in exchange for my honest thoughts.

CLEAN SOUND, AFFORDABLE PRICE​

As someone who has been searching for affordable, high quality and powerful sources, Fosi has always been under my radar for seemingly being the only brand that can offer all three in the market. Maybe it’s their marketing, but all other brands I’ve seen have fundamental flaws in the products I’ve tried that make it somewhat iffy to not only use but recommend to other people. Whether it’d be awkward volume shifts or an insanely inefficient and noisy sound, it’s a truly rare sight to see a brand come up with a fundamentally good source. So when I heard that Fosi was coming out with a combo DAC/AMP that can do 1100mW on 4.4mm Balanced for under $100, I just had to bite and taste what a package deal Fosi seems to be offering.

SPECIFICATIONS:​

Model SK02
Input USB/OPT
Output 3.5mm Headphone,4.4mm Headphone,3.5MM line out/OPT
Amp output maximum power 3.5MM：
High Gain: 280mW@32Ω, 130mW@64Ω, 40mW@250Ω, 30mW@300Ω
Low Gain: 90mW@32Ω, 50mW@64Ω, 15mW@250Ω, 10mW@300Ω

4.4MM：
High Gain: 1100mW@32Ω, 550mW@64Ω, 150mW@250Ω, 120mW@300Ω
Low Gain: 350mW@32Ω, 180mW@64Ω, 50mW@250Ω, 40mW@300Ω
Frequency Range 20Hz-20kHz (±0.02dB)
THD ≤0.001% @ 1kHz
SNR 3.5mm Headphone:
Low Gain:116dB
High Gain:120dB

4.4mm Headphone:
Low Gain:110dB
High Gain:115dB
Headphone matching impedance 16-300Ω
PC-USB Sampling Rate 32Bit/384KHz DSD256
OPT Sampling Rate 24Bit/192KHz
DAC Chip ES9038Q2M
Device Dimension 4.76*2*1.69inch (121*51*43mm)
Net Weight 0.84lb/380g
Power Supply 5V, USB Type-C

BUILD​

The SK02 is arguably the most unique desktop source that I’ve seen in a while due to it’s somewhat peculiar shape. While most sources are flatter and wider, the SK02 is taller and thinner with a somewhat brick-like shape.



Starting on top, you can find the bulk of the features of the SK02 with the Fosi logo up top, two buttons with the left changing gain modes and the right changing connection modes, the plethora of LEDs with the left side showing your current gain mode and your PCM decoding and on the right with the connection mode as well as your DSD decoding and power/volume status. At the very bottom is the massive infinite volume knob that also acts as a universal pause button by pressing down on the volume.



Moving down to the front side of the device, you can find the 3.5mm and 4.4mm jacks.



The sides are bare with just a solid aluminum panel wrapping them.



The bottom features the rubber stoppers.



On the back, you can find the inputs including the Type C, optical and AUX/Optical out.

While the build might not be so different from other desktop DAC/AMPs, the construction is sturdy and the interface is well-made. I don’t feel scared to wear out the jacks and the buttons feel tactile and satisfying. The knob infinitely spinning might be a problem for those who want a true analogue knob, but I’d say that it does the job really well and allows for a very fine level of volume adjustment. Plugging in jacks have a very satisfying click, especially on the 4.4mm which fills me with confidence that this won’t wear out quickly.

FEATURES​

One of the most surprising things about the SK02 is how much features this thing has for a sub $100 desktop amp.



Firstly, you get the aforementioned gain switch that allows you to change from low gain to high gain. The difference is VERY audible on both and can mean the difference between being able to drive something comfortably with good headroom and not having enough power.

This is thanks to the over 1100mW of power on high gain through the ES9038Q2M DAC and SGM8262 AMP and balance that makes the SK02 one of the best combo DAC/AMPs to drive high impedance and low sensitivity headphones. Besides dedicated amps, I don’t know other DAC/AMPs in this price range that has that high of an output.

You also get your usual mode switching from optical, USB or coaxial for those who would like to plug this into home theater setups.



But arguably one of the best features of the SK02 is how much information it provides on the top LED display. PCM decoding, gain mode, input mode, DSD decoding and power inputs are exactly the kind of information you wanna see while listening to music. This made me realize that MusicBee does NOT decode higher than 96kHz PCM on its own but Foobar with the SACD plug-in does. Being able to know what gain mode and connection mode are also very useful when troubleshooting or testing different gears. The argument could be made that they could’ve just made it more compact and just use different LED colors to indicate these things, but I’d argue this makes it easier for someone to know exactly what they’re playing.



You can also use the volume knob as a pause button that works surprisingly well for even applications that usually can’t get paused by the system. From foobar to MusicBee, if I pressed the volume button down, it will pause the music.

SOUND​

As someone who’s spent their time on portable dongle DACs as their main source for both mobile and PC and having only experienced a handful desktop options, the SK02 seriously impressed me with how much it opened out the sound of anything I plug into it. This is further compounded by the option to have a balanced output that makes this a seriously impressive source in both sound and power.

First off, the sound is properly neutral. I didn’t find this to color any of the headphones that I plugged into it. However, it does improve upon the strengths of whatever I plug into it. It opens up the sound and presents the soundscape in a cleaner, more transparent and nuanced way that is nothing like I’ve heard in any other source. I’ll explain more when I compare this to other sources, but I was ge nuinely impressed with the headroom I got with this and how much it improved everything I plugged into it.

Arguably the strongest sonic feature about the SK02 is how much it improves the dynamic range of the headphones I plug it on. The nuances in music, especially when listening to higher resolution files are evident with how the nuances are more prominent and the space in between instruments make music sound more immersive than other sources that I’ve tried.

This is further compounded when using the 4.4mm balanced as it opens up the sound further and gives you even more headroom and provides a very immersive listening experience unlike anything I’ve heard prior.

Pairing​

Normally, I have a favorite pairing for the sources I review. However, the SK02 is the one source that I found to pair with basically everything I throw at it. From the humble in-ears to my 500ohm beast of earbuds, the SK02 is more than capable of providing sufficient and clean power to give me a satisfying listening experience. I can pair almost anything with the SK02 with little to no issues, so pairing is very versatile.

Noise​

Despite outputting almost 1100mW, I never experience any issues when it comes to noise floor on even very sensitive IEMs on balanced output. I paired the SK02 with the Simgot EW200 with a balanced cable and I did not hear the noise floor.

USABILITY​

From the moment I set-up the device to the hours of listening I’ve put into it, the SK02 has given me a hassle-free and versatile experience as I often never have to think of anything after plugging whatever headphones and adjusting the volume accordingly. No complex instructions from the manual, no fumbling with the cables, buttons or connectors. Just the perfect definition of plug and play.

I really appreciate Fosi sticking purely with USB audio for both power and data as adding another power supply will just cause problems if you don’t have an outlet ready. Despite that, they were still capable of provide 1.1w of power in the measly 5V DC. At that point, it’s inexcusable how other companies can’t achieve that level of power and sound cleanliness in the budget segment.

The one thing that I will say that someone both impressed but bothered me was the form factor. While I do think that this form factor is great for those who want a slimmer footprint, the height forced me to place the SK02 elsewhere due to its height and not being able to fit into my desk without obstructing my monitor. I know it’s a niche problem, but it’s something to consider if you put your sources on your risers or in between areas.

Otherwise, I found 0 issues with the SK02 in my weeks of listening. I could not think of a single con of this product for the price and perfectly compliments everything I plug into it.

COMPARISONS​

First, let’s compare it to two of my other desktop options. The Topping DX1 Combo DAC/AMP and the combo of the NEOHIPO DC10 and Douk U3.

vs Topping DX1​

Prior to the SK02, the DX1 was my main desktop source. For the time, it was the best source I’ve ever had as it brought about the best in the IEMs and headphones I plugged into it with superb quality and headroom. This was when I realized that desktop sources were a completely different beast from the little dongle DACs I was used to.

Come today and I realized that the DX1 wasn’t even the best I could get in the budget. The SK02 provided a cleaner, more dynamic and more open listening experience compared to the DX1. The DX1 had a warmer tone that provided a more natural timbre and paired better with neutral bright headphones, but the SK02 was able to provide a more transparent listening experience while improving upon the dynamic presentation and cleaning up the transient response.

But arguably the biggest upgrade from the DX1 was raw functionality and features. The DX1 is just a DAC/AMP through and through. You get your analogue volume knob and a gain switch at the back, but that’s it. The SK02 has dedicated LED for decoding, gain modes and power all in the same side. No fiddling at the back to change gain modes. The DX1 does have RCA connection going for it, so you can use it as a DAC to pair with your headphones while the SK02 is limited to being used as a pre-amp through the AUX at the back.



On top of that, the SK02 features both a 3.5mm and a 4.4mm output that can do 280mW @ 32ohms on 3.5mm and 1100mW on 4.4mm Balanced. Compare that to the DX1 that only features 3.5mm and maxes out at 280mW, you start to see why the SK02 is just the superior source in general

While the DX1 has a place in my heart, I cannot deny that the SK02 is just the better device overall. More features and a more powerful sound at the same price makes the SK02 the clearly superior choice.

vs Neohipo DC10 + Douk U3​

This set-up is a newer set-up of mine as I wanted to get a really powerful source to pair with a nice pure DAC.

First things first, the SK02 wins in pure convenience. The amount of setting up you have to do to is something only enthusiasts would find enjoyable. You need to find a free outlet for the Douk U3, a decent RCA to connect the U3 to the DC10 and the USB that eventually plugs into the PC. The SK02 just needs you to plug and play. The space you need to setup both devices might also be a problem for some, but both devices are pretty small and you can stack them on top of each other to minimize the amount of space being taken.

As for features, the DC10 may have a very simple display but the tactile levers and straight forward dual LED indicators are perfectly adequate, albeit will require you to thoroughly read the manual to know what color is which. The U3 has an on and off switch at the back and an analogue volume knob. Unfortunately, this volume knob is borked as the sudden jump in volume means that this is practically unusable with in-ears.

The issue with the volume isn’t the only reason why this combo isn’t great for in-ears as the noise floor of the U3 really cannot pair with in-ears well. On less sensitive in ears, it’s perfectly adequate and actually enjoyable with the likes of the KZ PR3. But anything more sensitive than 105db and lower than 32ohms will just be a noisy mess. I understand the DC10 has basically nothing to do with that and I can use an op-amp to improve the noise problem a little bit, but the SK02 commits all those issues in a single, convenient package.



The only benefit to the U3 + DC10 combo is that you can essentially change either to improve your listening experience. Want a cleaner sounding amp to something cleaner, more powerful or has tubes? Replace the U3. Want a more feature rich DAC? Replace the DC10. But that means going out of the $100 budget that the combo asks for which goes higher without sales.

At that point, the SK02 is just the better device for those who just want a good source and nothing more. The combo source is great for those who like to DAC/AMP roll or want to think of the long term when one of the parts die and needs to be replaced. Versatility is also the strength of the combo, but at what cost? I’d personally just take the SK02 and call it a day, but I get the appeal of the combo and is still a viable choice for hobbyists.

CONCLUSION​

Whether you’re a casual listener or a power user, the SK02 might just fit into your set-up to have the best listening experience. A near seamless user experience paired with a very powerful output that rivals dedicated amplifiers that require a separate power supply isn’t something you see a lot, moreso under $100.

If we’re talking hard flaws, I really cannot think of anything that the SK02 is flaunting. Lack of mobile support? Get a dongle instead, there are many powerful portable dongles in the market today. Height? That’s justified, but it’s also slimmer than your usual desktop DAC/AMPs, so unless you have literally no more space anywhere else, the SK02 is genuinely the perfect budget reference desktop DAC/AMP you can get for under $100 today.

Thank you for reading my full review on the Fosi SK02. If you would like to order one, consider using the non-affiliated link below:
https://fosiaudio.com/products/fosi-audio-sk02-desktop-dac-headphone-amp

I recently had the chance to check out the Fosi Audio SK02, a new DAC/amp combo that Fosi Audio sent over for me to review. It's currently priced at $99.99 and you can grab it here. In this review, I'll be sharing my honest thoughts and experiences with the SK02, aiming to give you a clear picture of what this device has to offer. Let's dive in and see how it stacks up!



Starting with Packaging:



The SK02 is packaged minimalist. Inside the box, you'll find the DAC amp nestled alongside necessary cables (USB Type-C to Type-C, with fused Type-A Adapter) The packaging is very straightforward.

Affordable, All Rounder Desktop Dac Amp

Priced competitively, the Fosi Audio SK02 provides excellent value. It excels as an all-rounder DAC amp, offering solid sound quality, feature richness, and a sturdy build. For those seeking a potent DAC amp for IEMs that require high power, such as planar, it can drive any headphones on the market due to its high power output.

The Maximum Output Power:
- 3.5mm Output:
- High Gain: 280mW @ 32Ω, 130mW @ 64Ω
- Low Gain: 90mW @ 32Ω, 50mW @ 64Ω
- 4.4mm Output:
- High Gain: 1100mW @ 32Ω, 550mW @ 64Ω
- Low Gain: 350mW @ 32Ω, 180mW @ 64Ω
Other Specifications:
>Inputs: USB, Optical (OPT)
>Outputs:
- 3.5mm Headphone
- 4.4mm Headphone
- 3.5mm Line Out/OPT
>Frequency Range: 20Hz-20kHz
>THD: ≤0.001% @ 1kHz
>SNR:
- 3.5mm Headphone:
- Low Gain: 116dB
- High Gain: 120dB
- 4.4mm Headphone:
- Low Gain: 110dB
- High Gain: 115dB
>Headphone Matching Impedance: 16-300Ω
>PC-USB Sampling Rate: 32Bit/384kHz DSD256
>OPT Sampling Rate: 24Bit/192kHz
>DAC Chip: ES9038Q2M
>Power Supply: 5V, USB Type-C

Functionality Details:






Buttons and Knob: •Volume knob: It's smooth and precise, doubles as play/pause with a press, and powers on/off when held. While it's good, there are some cons with this type of smooth volume knob, like accidentally turning the volume up too high. • Left Button: Toggles between high and low gain settings, ideal for different headphone types. • Right Button: Switches between USB and line out modes, catering to various audio sources.

LED Indicators: • Gain Setting: Indicates selected gain level (high or low). • Input Mode: Shows active input mode (USB or line out). • Format and Sample Rate: Displays PCM or DSD format and sample rate. • Power: Indicates power state. • Volume Level: Displays relative volume via LEDs on the knob.

Disclaimer: I received a review unit from Fosi Audio; however, my review is impartial and reflects my honest appraisal.

Sound Signature:

This DAC/amp has a neutral-ish sound signature that's very transparent, though in my opinion, it's a bit on the dry side. I do sense a slight touch of warmth in the midrange, but it's not too prominent. Overall, it delivers a clear and detailed sound, which some may find a tad analytical. It's great for revealing nuances in music, but if you prefer a warmer, more lush sound, or bright more energetic sound, this is not the one.

Fosi SK02 Sound Signature by Genre:

The SK02's balanced sound signature lends versatility across different music genres:

Bass-Heavy Genres (EDM, Hip-Hop): ♪ The SK02's balanced bass suits these genres well, delivering deep bass extension without overshadowing the mids.

Note, its neutral character means bass may not be as pronounced as with bass-boosted amps, ideal for those preferring a less thumping low-end.

Acoustic Genres (Folk, Jazz, Classical): ♪ The SK02's slight touch of warmth adds body to instruments and vocals, enhancing the natural sound of acoustic music. It ensures clarity and detail, preserving the subtleties of the music.

Balanced presentation ensures clear vocals and instrument separation.

Rock and Pop: ♪ The SK02 offers lively performance for rock and pop. Guitars retain their energy, vocals clarity, and controlled bass without muddiness.

Its neutral signature preserves the artist's intended sound.

Metal: ♪ Metal benefits from impactful bass, and while the SK02 delivers solid bass presence, it may not satisfy those seeking aggressive lows.

Nevertheless, it maintains clarity, crucial for separating instruments in complex metal mixes.



The SK02 DAC chip is renowned for its neutral and transparent sound signature, which pairs well with various IEMs:

Tri i3 MK3: The Fosi SK02 complements the Tri i3 MK3 effectively with its 4.4mm jack delivering 1100mW, meeting the MK3's high power demand and unlocking its true potential. The SK02's neutral and clean sound preserves the overall sound signature of the Tri i3 MK3.

Dita Project M: The SK02's balanced sound and slight warmth in the midrange help to mitigate the brightness of the Dita Project M, renowned for its emphasis on the upper midrange and treble. This results in a more pleasant and controlled listening experience despite the SK02's transparent nature.

BQEYZ Wind: The Wind benefits from the SK02's clarity and transparent presentation, although it can make the IEMs' sound signature feel a bit dry. Nonetheless, this enhances the overall naturalness of the listening experience.

BQEYZ Cloud: The SK02's neutral and clean sound helps to balance out the Cloud's bright signature, making it less fatiguing for extended listening sessions, but it feels like the airiness of the treble and vocals diminishes slightly.

Additional Info:

The SK02 supports plug-and-play on most devices, requiring no additional drivers for Windows or macOS. For mobile use, it doesn't work with all phones somehow, my LG v60 is doing just fine, but Poco M4 Pro it doesn't work at all, also for phones user you should note that it may drain batteries significantly due to its power demands.

Phone Battery Drain:

The SK02 may significantly drain phone batteries compared to laptops due to phone battery limitations.
Phone: With a typical battery of around 5,000mAh, phones can really feel the SK02's power draw, especially when you're using high gain for demanding headphones or power hungry iems.
Laptops, with their larger battery capacities (typically ranging from 30 watt-hours to over 100 watt-hours), can efficiently handle the power requirements of devices like the SK02 without significant impact on battery life

Estimating Phone Battery Drain:

> Phone Battery Capacity: Most phones have a battery around 5,000mAh (or 5Ah at 3.7V, which is roughly 18.5Wh).
> SK02 Power Consumption: The SK02 uses about 2W.
> Phone Power Consumption: Phones typically use around 3W.
Calculation:
> Total Power Consumption: 3W (phone) + 2W (SK02) = 5W
> Battery Life (in hours) = Battery Capacity (in Wh) / Total Power Consumption (in W)
-For the phone: 18.5Wh / 5W = 3.7 hours
So, if you're pairing the SK02 with your phone, you might see your battery life drop to around 3.7 hours, This is just an estimate. Actual battery drain will depend on things like:

The specific phone model and its battery health, How you use it (volume level, high vs low gain), other tasks running or what else you're doing with your phone, examples using mobile data, and streaming the music makes the phones drain a lot faster though, etc.

Pros:
+Solid Build: The SK02 is constructed with durability in mind, suitable for both home and portable use.
+High-Quality Sound: It offers a balanced sound profile featuring deep bass, warm midrange tones, and natural highs, delivering detailed clarity across a wide range of musical genres.
+Ample Power: Boasts high output power to effectively drive even the most demanding headphones and IEMs, ensuring clear and powerful audio playback.
+Feature-Packed: Includes versatile connectivity options such as USB and Optical inputs, dual headphone outputs, and user-friendly controls like the versatile volume knob.
+Supports High-Resolution Audio: Capable of handling high-resolution audio formats up to 32Bit/384kHz PCM and DSD256, catering to audiophiles seeking enhanced sound fidelity.

Cons:
-Neutral Sound Signature: While its neutral sound profile is great for accuracy, it may not appeal to users preferring a warmer or more toward energitic or bright-is sound.
-Limited Phone Compatibility and also drain much battery: Not universally compatible with all smartphones due to power requirements, potentially causing significant battery drain during use. Its desktop DAC amp design makes it less suited for mobile applications.
-Volume Knob Sensitivity: The smooth-operating volume knob, while precise, could lead to unintended volume adjustments, which might be a minor inconvenience.

Overall:

The Fosi Audio SK02 is a great DAC/amp combo that offers solid value for its price. It packs a punch with its high power output, versatile connectivity options, and support for high-resolution audio formats. The sound is neutral, transparent, and detailed, making it perfect for various music genres. However, if you prefer a warmer or more energetic sound, this might not be your cup of tea. It's well-built and easy to use, but it doesn't play well with smartphones and can drain your phone battery quickly due to its power demands. Overall, it's a reliable and affordable desktop DAC/amp solution with excellent audio fidelity and plenty of power.

Summary
The Fosi Audio SK02 is a desktop dac amp coming in at 99$. Some of its highlights are, solid build, pretty high power output, very low noise floor, ease of use, big bold knob, both BAL and SE outputs and decent sound, etc.
So is it any good? Yes, this checks ofd all the boxes when looking for a desktop dac amp. This has plenty good features and additionally what I find appealing is the form factor and versatility, this is a great source for both iems and headphones. I would say this is like a dongle dac on steroids lol.



Intro
Hey guys, Whats up
Today I am checking out the Fosi Audio SK02. This is a budget desktop dac & amp combo coming in at 89$. This has been getting a lot of positive attention lately, is it actually any good? Lets discuss…

About the brand
Fosi Audio is a fairly new company in the international audio scene. Fosi Audio is a Chinese brand famous for their affordable source gears and amps. They recently started focusing on portable sources as well. Although this is my first Fosi product, I did try their DS01 dongle and some of their other stuffs.

Disclaimer: thanks to Fosi Audio for providing this unit. But as usual my review is unbiased and my honest opinion.



Specs

Packaging
Starting off with the packaging of the SK02, it is simple and straight to the point. This comes a simple blue Fosi branded box. Inside you will find a instruction manual, usb cable and the device itself, all neatly nestled in foam. Honestly the minimal packaging is pretty fair for the price.


Build and Design
Moving on to the build and design of the SK02, this is very well made. The device is made from solid metal, CNC machined aluminum to be exact. Design wise it is different from most other desktop dac amp at this price. Fosi has gone for a vertical layout with the buttons, knob and LED indicators on top. The top is also slightly protruded, giving the device a bit of character. The front side has the outputs (3.5mm and 4.4mm) and the back side has the inputs (USB C and optical) and line out. All the front and back ports are of good quality. The left and right side are blank. All the sides have rounded off edges. The device has substantial weight, feels good in the hands, and there are rubber feet below to stop it from moving around. The knob and buttons also seem to be made of metal.



Functionality:

Buttons and Knob
There are two buttons on the top of the dac amp, one is to change between high and low gain, and the other is to change input mode between usb and line out. The volume knob is one of the best parts of the SK02. It is an infinite rotate type of knob, and the rotation is in very gradual tactile increments. As you would expect the knob controls the volume, but additionally single press does play/ pause and press and hold turns power on and off.

Inputs
For inputs we get a USB type C port for both data and power, and an optical port.

Outputs
For outputs we get a 3.5mm single ended and a 4.4mm balanced on the front of the device and a 3.5mm line out on the back side.

LED Indicators
There are a total of 14 LED indicators showing the setting you are in. The indicators show cases: gain setting, input mode, PCM or DSD file format and sample rate, power on/off, and volume indicator.

Power Output
One of the more significant features of the SK02 is its power output. The SK02 boasts a wapping 1100mW at 32ohms in balanced and 280mW at 32ohms in single ended. The full list of power output at different impedance level is mentioned the specs list section. The power output from such small usb powered seems crazy, maybe a bit too good? I dont know, I do not have proper gear or know how to measure it, but performance wise this seems fine.


User Experience

Pairing with my gear
I used and tested the SK02 with several of my gear, I will put the list of devices I used below. I specially loved it with my over ears, because of its crazy power output and good sound.

Ease of Use
One of the things I really like about this device is the simplicity. Basically its a dac dongle on steroids . All you need is just ine cable for both power and data, and just plug and play. The form factor ie also really good. The big old knob is a huge added bonus.

Versatility
Another one of the most important things I love about the SK02 is its versatility. I mean, although this is marketed as a desktop unit, the form factor allows it time be portable. The high power output yet a very quite noise floor allows for a very acceptable listening experience both with sensitive iems to power hungry planar headphones (except for the crazy power hungry ones ).

The Cable
The included cable is good. This is unique that the C to C cable has an OTG adaptor built in with the cable. The cable is memory prone, but it is knit picking. Build wise the cable is average, maybe a bit above average when compared to the cables you get with other dac amps at this price.

Power consumption and heat management
I used the SK02 with my pc and my phone, mainly my phone though. With phone this sounds fine but this does drain the battery. With pc battery drainage is not an issue and due to the better power supply I feel like you get max power output. Heat management in this device is really good, it might get slightly warm when running for a while in high gain and high volume, but it never got hot.



Sound
Please note when it comes to sources the sound change are usually not that significant, this will not change the sound of your current gear, but rather will add flavor to it.

Now most importantly sound, is it any good? Yes it is plenty good I would say. Fosi has gone for a balanced, almost neutral sound, with a small touch if warmth. No matter what gear I throw at it, it holds up strong from sensitive iems to power hungry over ears.

Starting with bass, it has a very balanced presence. The quality of it is good, it goes fairly deep in the sub bass and the mid bass has nice punch. Bass texture and layering is good but nothing extra ordinary. Midrange of the SK02 is not exactly warm, but I would say has a touch of warmth. Vocals are pleasant with the right amount of crispness in female vocals and in upper mids in general. Treble is balanced yet natural. This handles bright sounding iems and headphones very well and makes it more pleasent. Soundstage is wide with decent depth. All in all this provides a great sound experience for the price.

Tested with:
IEMS: Simgot EA1000, Simgot EA500LM, Thie Audio Hype 4, Thie Audio Hype 2, Campfire Audio Andromeda
Headphones: Koss KPH30i, Sennheiser HD600, Aune AR5000, Hifiman Arya V2



Conclusion
To conclude the review, is this actually worth 99$? Yes, very much, this provides great value for the price with decent sound and many good features. Who is this for? If you are looking for a high power, small form factor desktop dac amp for headphones, look no further. But if you want to use only with iems and do not need high power output then I would go for dongles instead for the portability factor. So, do I recommend it? Yes, if the features meet your requirements. Anyways props to Fosi Audio, you have done a great job with this one. And big thanks to you all for sticking around, see yall in the next one

The Fosi Audio SK02 differs significantly from the SK01, which was solely an amplifier with an integrated battery. The SK02 enhances the device's design by incorporating an additional DAC, making it an ideal travel companion.
The device is well-made and costs under $100, making it an excellent bargain for audiophiles.


Specifications


Model : SK02
Input : USB/OPT
Output : 3.5mm Headphone,4.4mm Headphone,3.5MM line out/OPT
Amp output maximum power

3.5MM ：

High Gain: 280mW@32Ω, 130mW@64Ω, 40mW@250Ω, 30mW@300Ω

Low Gain: 90mW@32Ω, 50mW@64Ω, 15mW@250Ω, 10mW@300Ω

4.4MM ：

High Gain: 1100mW@32Ω, 550mW@64Ω, 150mW@250Ω, 120mW@300Ω

Low Gain: 350mW@32Ω, 180mW@64Ω, 50mW@250Ω, 40mW@300Ω

Frequency Range 20Hz-20kHz (±0.02dB)

THD ≤0.001% @ 1kHz

SNR :
3.5mm Headphone :
Low Gain:116dB

High Gain:120dB


4.4mm Headphone :

Low Gain : 110dB

High Gain : 115dB

Headphone matching impedance 16-300Ω

PC-USB Sampling Rate 32Bit/384KHz DSD256

OPT Sampling Rate 24Bit/192KHz

DAC Chip ES9038Q2M

Device Dimension 4.76*2*1.69inch (121*51*43mm)

Net Weight 0.84lb/380g

Power Supply 5V, USB Type-C




The Fosi Audio SK02 offers a neutral and analytical sound profile. The bass is crisp and well-managed, boasting adequate dynamics and texture. Notably, the sound signature leans towards neutral and bright, yet retains a touch of warmth in the lower midrange. The SK02's technical prowess is impressive, especially given its approximate $80 price point.

I consider it a valuable device to carry along, and I prefer to couple it with the SK01 to enhance the warmth of the sound.

INTRO


SK02 is a DAC/AMP offers portability and high power output driving music gear with ease. It a simple plug and play source which uses 3.5mm and 4.4mm Balanced terminations. The multifunctional volume knob is huge plus for a portable DAC/AMP you can adjust the volume to your liking in a most convenient way.


Disclaimer


I would like to thank Fosi Audio for arranging a unit for me. My opinions are unbiased, and I haven't been influenced or instructed to praise these gear. Every detail in this review is actual experience made by listening for hours everyday.






Specifications


Model : SK02
Input : USB/OPT
Output : 3.5mm Headphone,4.4mm Headphone,3.5MM line out/OPT
Amp output maximum power

3.5MM ：

High Gain: 280mW@32Ω, 130mW@64Ω, 40mW@250Ω, 30mW@300Ω

Low Gain: 90mW@32Ω, 50mW@64Ω, 15mW@250Ω, 10mW@300Ω

4.4MM ：

High Gain: 1100mW@32Ω, 550mW@64Ω, 150mW@250Ω, 120mW@300Ω

Low Gain: 350mW@32Ω, 180mW@64Ω, 50mW@250Ω, 40mW@300Ω

Frequency Range 20Hz-20kHz (±0.02dB)

THD ≤0.001% @ 1kHz

SNR :
3.5mm Headphone :
Low Gain:116dB

High Gain:120dB


4.4mm Headphone :

Low Gain : 110dB

High Gain : 115dB

Headphone matching impedance 16-300Ω

PC-USB Sampling Rate 32Bit/384KHz DSD256

OPT Sampling Rate 24Bit/192KHz

DAC Chip ES9038Q2M

Device Dimension 4.76*2*1.69inch (121*51*43mm)

Net Weight 0.84lb/380g

Power Supply 5V, USB Type-C






Packaging

Fosi Audio Sk02 Headphone Amp
2-in-1 USB-A/C to C Cable
User’s Manual


Build and features

The build is made from aluminum CNC ensures solid durability and long lasting use.

The Multifunctional volume knob serves as volume adjustments, play/off button and to turn on/turn off the SK02.

It also features low/gain mode buttons for quick switching to your liking

The light indicator helps the user to determine the sampling rate of songs.

The high power output of SK02 whooping 1100mw driving mostly of your gears with ease.


Sound Aspects

Fosi Audio SK02 sounds neutral and analytical. Bass is clean and well- controlled it has enough punch and texture. I just want to emphasize the highs have more bite lowering the volume help this department. Technicalities is above average for the asking price. It picking up enough micro details and nuances as well as creating wide stage performance.


Source used :

Rosetechnics Quietsea
Tangzu Xuan NV
EPZ Q1 Pro
Letshuoer DZ4

DDHIFI TC05 Cable
Stock Cable

This DAC spend 30-40 hours of burn in before taking details of this review


Pairing






With Rosetechnics Quietsea

The bass shows tactility and more punch. The V shape tuning of quietsea affects the mids become recessed but with sk02 it helps the mids to make more frontal presentation. As for the highs it has more bite and crisper quality.






With Tangzu Xuan NV

It is a neutral-warm tuning benefits more with this SK02. It shows more controlled and textured bass. Mid is smooth and lusher. Vocals is airier and more intimate. Treble is still safe and engaging enough to enjoy the presentation.






With EPZ Q1 Pro

Another harmanish tuned gear synergized well with SK02. It has already full sounding bass but when paired the bass takes it to another whole new level. It is tighter, punchier and well controlled. Mids is airer and more frontal. Treble is livelier and engaging. The technicalities have noticeable improvement such as imaging snd layering.






With Letshuoer DZ4

A neutral gear which focuses vocal clarity. It has clean and coherent sounding bass which not appealing to everyone. The mids is the star of the show here the techs of SK02 helps this department. The vocals is lusher, airer and more intimate presentation. Also it helps the treble of DZ4 a little livelier.






Conclusion

The SK02 is a versatile DAC/AMP that you can carry on the go or some desktop setup. This is the most powerful DAC/AMP I've used in this price range whooping 1100mw which is crazy imo it can drive whatever your gears is. I'm easily recommend this SK02 for those people who looking for a budget decent desktop setup.

Review on my site: https://jamesfiorucci.wordpress.com/2024/05/11/simple-audio-review-fosi-audio-sk02/

Fosi Audio are a Chinese HiFi brand famous for their budget audiophile gear. They make a variety of dongles, DAC/amps, preamps and more, with the majority of their products falling below $100 in price.

Their latest DAC/amp, the SK02, is one of their pricier units at $119.99, but can still be considered a budget-friendly device. Its development and manufacturing was funded with the help of a Kickstarter event; boasting over one watt of power and a huge knob (!) on a compact frame it was bound to secure the funding from the get-go.

The SK02 has been out for a few months now, and admittedly I’m a little late to the review party. I’ve been inundated with a mountain of gear which needs reviewing, which to be fair is a brilliant problem to have! This little DAC/amp has received plenty of positive reviews and is already being lauded as a benchmark in the sub-$150 price category.

Question is, do I agree with the general consensus regarding the little Fosi? Let’s start with what’s included.

Thank you to Cathy from Fosi Audio for organising a review unit for this evaluation.

What’s Included​

You don’t get much with your SK02. The box itself is a simple cardboard affair, and inside is the DAC/amp itself, the USB cable to connect to your playback device and a user manual.

Focussing on the cable, I’m a big fan. I love the interchangeable USB-A and USB-C connectors which are attached to one another. Makes it easy and simple to swap between using the SK02 with your mobile phone and your PC, as an example.

Clearly, the vast majority of Fosi Audio’s budget has gone into the unit itself though. Onto that then.

Design, Build and Features​

The shape of the SK02, along with its unique top-mounted volume knob, is reminiscent of the Micca OriGen series of DACs. The location of the volume control makes it easy to make adjustments, although I do wish it had a mark on its surface so you could remember preferred positions for certain headphones.

I think the whole layout of the LED indicators on the top of the unit to denote the sampling rate, and the simple gain and mode buttons to switch between high and low, and USB and optical respectively, are simple to understand and easy to read.

The knob itself functions as a play-pause button with a single press, and as a mute button when double-pressed. This is a feature I wish to see more on other similar devices.

At the front there is a single-ended 3.5mm and balanced 4.4mm output. And at the back is the USB-C input which acts as the data transfer and power draw for the device. The SK02 can be used as a standalone DAC courtesy of its aux/optical output, and as a preamp using the optical input.

Moving onto build, this is one sturdy piece of kit. It is manufactured out of an aluminium alloy that adds considerable heft; you could use the SK02 as a blunt force weapon in a pinch!

The weight, as well as the overall chunkiness of the unit means it’s not quite as portable or transportable as the small footprint may suggest. It will most likely stay firmly put to one side of your desk.

Sound and Synergy​

With a headphone output power of 1,100mW (@32 Ohms) from the balanced connection, the SK02 packs a serious punch. It’s certainly the most powerful amplifier that I’ve come across at its price point. The unbalanced connection still provides plenty of power with 280mW at 32 Ohms.

Suffice to say the SK02 will provide more than enough volume for even the most demanding and power-hungry of headphones. But will you want to? I’m not so sure, let me explain by describing its sound.

This is a very neutral-sounding device, with a slight sharpness to the treble frequencies which at times makes it sound a touch bright. This feature is a double-edged sword, pairing well with bassier headphones but accentuating any sibilance or harshness apparent in treble-focussed headphones.

Take the Beyerdynamic DT880 Edition 600 Ohm for example. It is renowned for its elevated treble, but with a decent enough amplifier the upper frequencies can be smoothed out quite nicely. Unfortunately this is not the case with the SK02, which not only has that slightly bright characteristic but also doesn’t have enough juice to tame that typical Beyerdynamic treble spikiness. Admittedly I could only use the unbalanced output with the DT880; perhaps it would have had a better time of things with a balanced connection.

I enjoyed the SK02 with my Denon AH-D5200 as well as the Sony MDR-1A. Both of those cans are on the bassy side, and the slight etch to the treble helps bring out the sparkle and details that otherwise can get lost around the heightened bass. It also helps that the SK02’s extension on both extreme ends of the frequency response is very good, and macrodynamics is decent too.

Imaging and soundstage performance is subpar on the SK02. This only becomes an issue on headphones that image particularly well, like the Audio-Technica ATH-R70x. The soundstage was squashed in by the SK02 and the layering capabilities became a little muddled, but don’t get the idea that it’s bad. It’s just about middle-of-the-road in the sub-$150 price category for integrated DAC/amps.

Overall Verdict​

The Fosi Audio SK02 DAC/amp impresses with its simple yet user-friendly design and jaw-dropping power output for its budget pricing. When it comes to the sound performance however, the SK02 is not without its flaws, but for $119.99 it’s really just a nit-pick.

Rating: 7/10​

Fosi Audio SK02

Prelude:
Fosi Audio is quite an interesting brand offering inexpensive and very functional audio equipment. Fosi Audio focuses primarily on excellent value for money and strictly adheres to the set standards. The first product I have the opportunity to test and evaluate is the SK02 model. It offers very good functionality at a very decent price/ SK02 is an all in one device and combines the functionality of a headphone amplifier with quite high power and a quite good digital-to-analog converter. This time the AUX input was omitted, instead offering us an optical input and output, both optical and linear DAC output. This is interesting and important because the Fosi Audio SK02, which costs approximately USD 119, can be a fully functional digital-to-analog converter and work as an output from a console or TV.


Unboxing and ergonomics:
In terms of packaging, it is a fairly standard cardboard box, containing the device itself, the user manual and a USB C-C cable with an adapter for classic USB. There are some compromises and savings here, but thanks to this, Fosi Audio maintains great and competitive prices, offering surprising performance at a very affordable price. Let’s take a closer look at the design of the SK02 itself. The device consists of a matte black block of uniform metal. Despite its armored construction, it is not heavy, or rather I would call it solid. At the top of the device there is a knob with infinite rotation, which also serves as a button to turn the device on and off, and also allows you to adjust the volume or pause the music. It is solid and holds securely to the mount. Overall, I can praise Fosi Audio for its high quality of workmanship. We also have a 3.5mm and 4.4mm ball output at our disposal. But that’s not all, we also get a 3.5mm LINE out and optical input and output. Of course, we also have USB C, which is used both to transmit sound and to power the device. Honestly, the SK02 offers a surprising amount of power (up to 1W into 32Ohm at high gain from the balanced output). At the same time, the SK02 maintains a very small, pocket-sized size. Which makes it the perfect companion for your desk or even on the TV stand. I wouldn’t call it a portable device or a dongle, but I would definitely call it compact and mobile. If I were to notice something, there are many markings at our disposal, but I would prefer a more clear marking of the volume, because it is easy to damage the headphones if the device is set too loud. At this point, I really appreciate EarMen’s patent in which the device resets the volume to minimum every time we turn it on, thus protecting our hearing. However, this is a marginal comment, and at this price it is not a problem. Speaking of markings, on the front of the device we will find a gain button, an input switch, a diode informing us about sampling, and an audio input button. Additionally, we have a green LED when the device is turned on and a volume LED that flashes purple.

Sound:
For my tests, I used very sensitive IEM headphones, the FirAudio E12, and my favorite full-size headphones, the HE1000SE from HiFiMAN. I played music from tidal.


Bass: The low tones are properly controlled and delight with their purity and neutrality. Fosi Audio SK02 is certainly a neutral device, focusing on transparent sound with a slight hint of warmth. The bass tracks were properly enhanced and the lower bands were properly accentuated. Importantly, the lower bands were in no way overwhelming or overly softened. Overall, I rate the sound of the SK02’s lower bands as very balanced and close to neutral. Actually, I wouldn’t lie if I used the term reference in relation to SK02. The tuning used in this device is a reference with a delicate musicality. It is true that it is not yet at the same level as in much more expensive products, but if someone is looking for a linear and coherent device, Fosi Audio SK2 will be a great choice.

Musical midrange: The midtones are linear in the case of Fosi Audio SK02, still retaining a neutrally warm tone. Importantly, the vocals are practically on the same line as the bass and treble. This proves very good tuning and a signature that is very rare in equipment in this price range. Additionally, we can certainly expect a lot of detail and a detailed, full sound. When it comes to the sound stage, it is both wide and boasts excellent depth, which makes the sound of the Fosi Audio SK02 complete and saturated. It may not be a spectacular and entertaining tuning, but instead it offers a neutral and analytical sound, which I personally value very highly. The space and separation of instruments are at the highest level, offering excellent parameters for the price range in which the SK02 is classified.

Treble: Maintains the overall neutral and linear tuning character of the SK02. At the same time, they are well stretched and offer a lot of details and information. In the case of quite crowded songs with a lot of information, Fosi Audio SK02 performs very well, offering excellent sound quality and not getting lost under the mass of information. The upper midrange is smooth and consistent with the overall sound offered by the Fosi Audio SK02. Although such a presentation may be slightly boring, it allows for a thorough analysis of the sound and provides a completely clean linear sound. When it comes to signal purity, Fosi Audio SK02 provides a clean signal, which is an additional advantage.

Comparisons:


Fosi Audio SK02 ($119) VS Fiio K11 ($119)
In terms of software and number of functions, Fiio K11 definitely wins because the digital display and support for cocial input offer great convenience. However, the Fosi Audio SK02 is much more compact and does not require a separate power supply, which saves even more space. Both devices have a quite similar sound signature with neutral analytical tuning. However, in my opinion, the SK02 is slightly warmer, while the K11 offers an even more digital sound signature. Both devices are really great and have a very high value for money. In terms of sound, it’s practically the same level. While the K11 wins with the number of functions, the SK02 wins with its compact and much smaller form. It all really comes down to what sound signature we’re looking for. Both devices are great and offer excellent parameters at very decent prices. If I was looking for a slight warming, I would definitely go for the Fosi Audio SK02, but if I preferred a slightly more ruthless and even more neutral sound, I would choose the K11.

Fosi Audio SK02 ($119) VS xDuoo xp2pro ($149)
I know that this is a slightly different product category, but they have some common features. First of all, both solutions are dedicated as portable products, with xDuoo xp2pro fitting into a small box and being much more compact. However, in terms of sound, Fosi Audio SK02 sounds more resolved and wider. In terms of power after balance, Fosi Audio SK02 certainly has more power, while in the case of the SE output, the leader will be xp2pro. In terms of sound, the xp2pro offers a more entertaining sound, while the SK02 focuses on tonal balance.

Line Out:
In terms of line output, the Fosi Audio SK02 provides a very pleasant sound without adding much to the natural sound signature. This is due to the ess ES9038Q2M DAC chip and chip, which is famous for its neutral and complete sound. Therefore, even for the line output alone, Fosi Audio SK02 is an excellent and very competitive device.


Summary:
Fosi Audio SK02 is a piece of great equipment. It is a budget amplifier and digital-to-analog converter dedicated to headphones. Enclosed in a very compact housing. It offers support for digital outputs and inputs and excellent technical parameters. Its undoubted advantage is also a very good line output and excellent sound quality. However, I would like to have more secure volume control in the future to better protect the headphones and hearing. Apart from that, it’s hard to find any flaws because it is a well-designed product and well thought out in every aspect. This is an interesting alternative for people looking for a small desk amplifier, for example for work. Fosi Audio SK02 offers not only a balanced and linear sound, but also a very transparent presentation with a large sound stage. That’s why I’m quite impressed by the great possibilities offered by such a small device at a price of only USD 119. In my opinion, this is a complete all in one set for all beginner audiophiles, or for people for whom saving space is crucial. Fosi Audio SK02 is very solid and durable.

Introduction!
Friends, I welcome everyone, today in the review we will look at a DAC amplifier from the company FOSI AUDIO, called SK02 and I’m sure you probably saw it in my previous reviews of different headphones and I used it for several weeks to test it thoroughly and share my operating experience.
It comes in a very small standard box with essentially no information about this device other than this sticker SK02.

Let's take a look at what's included!
The set here is very small, we get
1.Headphone Amplifier
2.USB Type C cable two in one with this adapter.
3.User manual in several languages.

Still, I like the way this amplifier looks.
And on the front panel it has 2 buttons, one for switching the gain mode from low to high, and switching the USB mode to optics and vice versa, and under it there are quite bright LED indicators that display the sampling frequency of PCM and DSD and this is 64.128 or 256 , and by the way, the amplifier weighs 380 grams.

And the all-metal round knob here has endless rotation and tactile pleasant clicks that you can feel when you turn the knob, and you can press it like this once to play or pause the music and if you press and hold, you can turn off the power, and from the unusual thing, here is a purple volume level indicator that flashes when playing low frequencies in the track, and this is a rather unusual sight, I’ll tell you.
But on the rear panel there are 3 outputs, namely usb type c for connecting, for example, the supplied cable, as well as one optical output and an AUX 3.5 mm port for outputting an analog signal.

And in front there is a balanced output at 4.4, and a standard 3.5.

And the DAC we were given here is probably already familiar to everyone: ESS9038Q2M with a separate operational amplifier SGM8262.
The output power at high gain is 280 mW at 3.5, and as much as 1100 mW for the balanced output 4.4, so it will swing your in-ear and full-size headphones easily and with a very large margin and excellent control, so you don’t even have to worry about it here, and I advise you right away switch to high gain because even then the amplifier remains only slightly warm even after long sessions, so we get a lot more power, although the first time I got it I only listened to it at low gain, and even then it drive without problems even planar headphones with a large margin.
Well, of course, the DAC works without problems and is detected on Windows, MAC OS, Android, and iOS no additional drivers need to be installed for it everything is picked up automatically.
How about sound?
And now, friends, let's talk about the most important thing, namely the sound of this device, which has excellent measurements, which can be found in more detail on the official website of Fosi Audio. I will specifically leave links in the description so as not to waste time analyzing all this now
And I’d better start with the fact that I tested with it both various planar in-ear headphones and hybrid and dynamic full-size headphones in different price categories!
Since it offers us excellent transparency and excellent localization with a wide stereo panorama with literally crystal clarity and outstanding resolution in no way inferior to my Topping g5, and its frequency response is absolutely linear in measurements, as it should be on modern sources, I hope you agree with me!
And the overall sound signature here does not feel analogue softened and warm, but has a strong bias towards that same cold monitor quality, which I very much approve of.
And I can absolutely say that this amplifier does not try to bring anything of its own into the signal and it has absolutely what it should have: a neutral, honest sound signature with good technique and highlighted attacks, without any brightness or additional warmth, that is, again, like me and said in previous reviews of DAC amplifiers, everything here will depend on your headphones that you are going to connect to this excellent and most importantly powerful source, since it will allow you to use planar headphones such as LETSHUOER S15 or Hidizs MP145 without problems and they will sound very correct on it with amazing control and technicality and in terms of attacks and transient processes, there will also be complete order here, but what can we say about hybrid headphones, which also open up as expected and this DAC does not constrain at all and does not try to blur the sound of the headphones in some super magical way, which is especially cool to hear from some audiophiles, I hope you understand what I'm getting at.
My conclusion on this dac:
Fosi Audio Sk02 is an excellent, very high-quality DAC for a small and pleasant price, with amazing power and the most mature neutral sound, all you have to do next is find good headphones and enjoy the music, and my reviews will help you with choosing headphones.
Link where you can buy this dac!
Fosi Audio:https://fosiaudio.com/pages/desktop-dac-headphone-amp-sk02
I will be glad if you subscribe to my YouTube channel and watch this full review on FOSI AUDIO SK02!

TLDR version on YouTube: TDLR - Fosi Audio SK02

The Fosi Audio SK02 is the latest device released by the brand and has been sent to me directly by Fosi Audio for me to try it out and to share my opinions in this review. Fosi have not made any requests except for asking if I could publish my review around the 26th of February, which is when the product will be officially released. It is currently available (at the time of putting this review together) on Kickstarter as a preorder (for around 65€).

Therefore, as always, I will do my best to be as unbiased as possible in my review.

The SK02 is available from various sources that I will leave links to on my blog.

As usual, links that I share are non-affiliate.



Intro…

Fosi Audio are not a new brand, they have been around for a while and produce audio amplifiers and related products at a fairly budget level. They are not the cheapest you can find on places like Amazon or Aliexpress but they are a brand that is serious about what they do and do it at a very reasonable price point.

I previously reviewed the K5 Pro here on the channel and today we have the SK02, which is another DAC/Amp combo but in a different form factor (and with different specs).

This small desktop all in one features and ES9038Q2M DAC chip (I am actually told it uses 2 of them), which has been used in quite a few devices before by many brands. In this case, Fosi have paired it with an SGM8262 OP Amp, which is also something we have seen before in other devices.

The specified power output (according to the Fosi Audio published spec) is 280mW @32Ohm (unbalanced) and 1100mW @32Ohm (balanced). These are quite powerful numbers and are almost double, in the case of the balanced output, to what I have seen specified from other models in the past using the same OP Amps.

But we will talk about power in just a moment, let’s first take a usual look at packaging and presentation.



Presentation…

There is absolutely no doubt that Fosi Audio spend as little as possible on the packaging in order to keep the price down. Well, I guess they could go with just a generic brown box or even just a padded envelope (it wouldn’t be the first time I have received devices packed just in an envelope), so lets say that the go for the cheapest branded packaging they can.

The box is the same a the one used on other Fosi products and shows the Fosi Logo on the front with the model name added by means of a sticker in the top right corner. There are no specs about the product on the box (which is understandable as it is a generic box for multiple products) although it does mention that you have a 30 day return period, 18 month warranty and lifetime technical support. Of course, if you are buying from Amazon here in Europe (or any other European seller), the warranty will be the legal minimum of 2 years or longer, depending on which country you reside/buy it in (Spain is 3 years).

Opening the box reveals a simple foam cutout that contains the DAC/Amp, the user manual and a USB-C to USB-C cable with an attached USB-A adapter.



Build and aesthetics…

The form factor is different to the majority of small all in one DAC/Amp combos as it is focused around having the volume control and information leds on the top of the device. This is a layout that will work better or worse for you depending on how you intend to set up and place the device.

The shell of the device is aluminium in a black finish and while it is not extremely heavy, there is a bit of weight to it to stop it being easily dragged around the desk when in use.

I am a fan of this style of device for places like my work desk as it provides a small form factor that can sit at the side of my keyboard and USB microphone, with easy to access volume control and easy to read status LEDs.

The overall build quality is pretty good, with rubber strips on the bottom to also stop it from sliding easily. The volume knob does have a slight wiggle when rocked side to side but it is not bad and is not really noticeable when using the device, just when actually focusing on rocking the wheel.

The majority of the status LEDs are orange and are bright enough to see but not bright enough to be distracting, something that I am grateful for when having it within eyesight on my desk.

While I wouldn’t say that the SK02 stands out as an incredible build or has eye catchng looks, I do think that it is well built and really can’t fault it for the price range that it sits in.



Functionality…

On the top of the device we have a large volume knob that also serves as a play/pause button and a power switch, at least on Windows 10. The knob is an infinite rotary style, so you can turn it endlessly and the only real feedback in regards to level is the amount of sound coming from your headphones (or speakers). Well, I guess that is not really true, as there is a volume level LED but that is a single LED that works sort of like a clip LED on a console or other device. By this I mean that the LED only really starts to flash as the volume level starts to increase, flashing brighter and longer as the volume increases. It is a nice touch and I appreciate it being included but it really isn’t something that will give you a real idea of the level.

The volume from the SK02 is independent to that of Windows. By this I mean that the setting of the SK02 in the Windows mixer does nothing. No matter the level set, it will allow the full range of the SK02 to be used and turning the volume knob does not adjust volume in the Windows mixer, it is separate amplification on the device itself. This is something very positive in my opinion as you can use exclusive modes in apps like Tidal or Foobar and not have to worry about it blasting sound through your headphones but it also means that you have to reduce volume with the knob and keyboard shortcuts will do nothing (including mute).

The rotary knob is also a push down switch which plays or pauses the music (or Youtube video etc.) when pressed once. A long press of the knob switches the SK02 off, which means you can disconnect the device without having to unplug it. A long press to switch it back on and the device reappears in Windows almost instantly.

Above the knob, the centre of the top panel features 14 mini LEDs. As I said a moment ago, the majority of these are orange, with only the volume status LED being a purple colour and the power LED being green. To be honest, I don’t really see the need for the power LED as there are always other LEDs active when the device is on anyway, but at least it makes the layout symmetrical.

The LEDs are in two columns of 7, with the left column showing (from top to bottom):

High Gain

Low Gain

384 PCM

192 PCM

96 PCM

48 PCM

44.1 PCM



The right hand column, again from top to bottom, shows:

Optical Input

USB Input

256 DSD

128 DSD

64 DSD

Volume level status

Power



These are all identified by small white text which is simple but easily read and nicely laid out.

Above the LEDs, at the top of the panel, there are two push buttons that sit flush with the device. The left button switches the Gain level, while the right button switches between the two input modes.

On the front of the SK02 we find the headphone connectors. These are a 3.5mm unbalanced connection, with a 4.4mm balanced connection below. The 3.5mm connector is slightly off center in comparison to the 4.4mm directly below, I am guessing due to internal space restrictions. This is only really a minor thing to point out and not a complaint as you only really notice it when looking straight at it.

The sides of the device are empty of connections and moving around to the back panel we find a USB-C input, an Optical input and a 3.5mm preamp output. The output is controlled by the volume knob (hence being a “preamp” output) and is muted by inserting headphones into the headphone output.

Something that I discovered while recording the Spanish video review is that the 3,5mm output is also an optical output, allowing the SK02 to feed other systems digitally. This is something that I always find handy and is nice to see on a budget device.

That is about it as far as functionality, plug in your cables, choose your mode and volume level and that’s it, away we go.

The only real comment I have here is that I think a microphone input would have been a good idea for this kind of device, similar to the one on the K5 Pro or maybe even just a TRRS for the 3.5mm to allow the multiconnector to be used. I am not talking about a high end microphone input, just something simple to allow gamers to use their headsets with this device, even if the mic volume would only be controlled in Windows. This is by no means a complaint, just a comment, exactly the same comment I have made with other similar devices in the past.



Sound…

I have not measured the output power of this device and I am still sceptical about the 1100mW claimed for the balanced output but I have to say that it is a very powerful little device. There is no exact volume meter for me to be able to tell you at what volume level I have been using this amplifier but I have certainly not been anywhere near max level with anything I have plugged into it. In fact, as a quick example, if I set the SK02 to full and then raise the volume in Foobar (as the Windows mixer does nothing), with the KPH40 on low gain, my usual listening levels are around -25dB and -15dB starts to be far too loud for me.

As far as sound, I will make my usual disclaimer that differences in sound between sources are usually very minimal, often exaggerated by reviewers to get our point across and most probably more based on our brain's interpretation than actual differences in sound. Saying that, I find the SK02 to be neutral edging very slightly towards the warm side of neutral. Not warm as in iFi style but certainly not cold and clinical like a THX. I would say it is similar in this style to something like Earmen or maybe Aune, although not quite at that level.

There is no real sensation of it adding anything to the sound, I think it is more that details are ever so slightly rounded, giving it a bit more of a smoother response which means that it is not going to be quite as detailed as some of the other brands and models out there but it is far from being a bad music reproduction.

Testing it with sensitive IEMs I found that, especially as the volume level raises, there is a presence of some background noise. However, I found it difficult to judge if it was the actual noise floor of the amplifier itself or if it was just making the noise of the track more than I am used to. In order to test this further, I used a silent track (basically a recording of silence) and found that I could max the volume with the same IEMs without hearing any of the background hiss, so my conclusion is that, for some reason, it is making the background noise present in recordings a little more noticeable than I am used to.

NOTE: As a safety disclaimer, I strongly recommend that you do not do this test! I was using Foobar with the output via Wasapi to the SK02, which means that “in theory” no other sounds could access the device. However, if something had gone wrong and something that was not silence had managed to play (i.e: another track or a windows notification), then I would probably have damaged both the IEMs and my hearing. Again, please don’t try this at home!

Anyway, back to the sound. As I said, it is neutral edging towards warm and I found that it works pretty well with both IEMs and headphones that are easy to drive, having more power than I would ever need. However, with the KPH40 (60 Ohms & 101dB) and the HD6XX (300 Ohms and 103dB) that, when pushing the volume a little higher, things didn’t seem to be quite as clean, especially when the track had a decent amount of bass. It is not that it sounded terrible, just that they seemed to have a little bit of congestion going on in the upper mids and treble when there is a good amount of bass.

This is something that I did not notice with lower Ohm headphones, even those that have lower sensitivity, nor did I notice it with higher Ohm IEMs, so I am not sure what is going on there. I just get the feeling that things are not quite as clean as they could be in these cases.

I also put some planars to the test with the SK02 and while it did a decent enough job, I did find it struggled to keep up with fast moving bass content on some of them such as the Arya v2. With the Ananda and the Edition X it didn’t suffer as much but I would still say that it lacks enough current to be able to move planar headphones properly, at least those that I have. This is also understandable as it is powered by USB and is a fairly small device.

With IEMs and easier to drive headphones, I found performance to be more than adequate for the vast majority of people who would contemplate having this on their desk.



Conclusion…

Again I find that Fosi Audio offers a device that is going to appeal to a lot of people. I don’t think it is really aimed at the audiophile crowd but more at the general music listener/lover that wants something small and compact for their desktop.

I also think that it is a good option for the gamers out there who use independent headphones and a USB mic. It is plenty powerful and is very easy to adjust on the fly, while taking up about the same amount of real estate as a mouse.

It can also be hooked up to a secondary source via its Optical input, and serve as a preamp to speakers via the aux output, so again, it is something that could serve a lot of people at a very reasonable price.

____
As always, this review is also available in Spanish, both on my blog (www.achoreviews.com) and on YouTube (www.youtube.com/achoreviews)

The Fosi Audio SK02 Dac Amp the latest in Fosi's SK line, it uses the Sabre ES9038Q2M dac chip and SGM8262 opamp same as what FIIO uses on the powerful KA13 dongle and supports up to PCM 384khz, DSD 256 and with an ouput power of 280mw @ 32ohms on 3.5 single ended and 1100mw on 4.4 balance.



It has the same design and built quality of Fosi SK01 amp basically bullet proof metal brick and probably will outlast all my audio gears, on the faceplate it sports 2 buttons for gain and mode usb, optical and below it are the led indicator lights and the solid metal knob with infinite rotation with tactile clicks you can feel when turning the knobs, push the knob once to play/pause push twice to mute/unmute and long press to power on/off, at the back you see 3 inputs, usb type c for input and power since the sk02 in usb powered, there is also 1 optical input and the 3.5 doubles as a analog output and optical out.



Fosi audio did a great job on the implementation of the ES9038Q2M dac chip, its not too warm analog sounding not also cold too bright and technical sterile sound its somewhere inbetween, like they hit the sweet spot. it has a natural neutral clean tone that you get to capture micro macro details in all musical genre you put it through without sounding too digital and a well defined accurate bass though on some tracks i tested it sometimes lean a little bit on the brighter side which also gives the sk02 good details and resolution. with an output of 1100mw on balance it can open up most hard to drive over-ear planar headphones as well as iems. you certainly get more than you paid for sure. Great job Fosi Audio, looking forward to SK03... perhaps making future models more portable and power efficient. SK02 is a fun dac that delivers and performs more that its worth.
True to their word ''HiFi Made Fun''!

Iems i used for testing : Tanchjim Zero, Simgot ea500, Hidizs mp145, ARTTI T10.
Over-ear headphones : Hifiman HE400se.

https://fosiaudio.com/pages/desktop..._xGjSAjHvSJmmFvZ0UGbXyoF5SJUjRb9DPsDhPxkBBCQ4

POOWWWEEERRRR!!!

~~Terry Crews in an old Old Spice commercial.


FOSI AUDIO is one of the few audio companies out there that offers some of their products that truly signifies that price to performance statement on how they manage to construct them meticulously. They usually specialise in producing amplifiers and preamps, and they were able to offer at a very affordable price.



I actually did a review on their product before and I still have a pending item to review from them. What I have here right now to be feature in this review article is their latest Desktop DAC/ headphone amp, The FOSI AUDIO SK02.



The SK02 is a desktop-grade headphone amplifier in which its overall construction is quite solid yet compact as it allows me to carry it anywhere due to its balanced weight for a desktop amp. It has an elongated square shape chassis made of solid aluminium alloy which underwent a process via CNC milling and its surface which were sandblasted to achieve that matte-like finish.



At the top panel, there are some buttons for gain and input modes, some levels of LED indicators for gain display, PCM sampling rates, DSD sampling rates, volume level status and power indicator that were aligned horizontally, and a large multifunctional knob use to adjust for volume control on clockwise/counterclockwise and clicks for basic command functions.



On gain modes, it offers two modes that will be beneficial for headphones and earphones with different power output requirements from very sensitive IEMs up to the power hungry cans with magnetic planar drivers. These modes are low gain and high gain mode, and the difference between two modes are quite a stark contrast in terms of power output delivery, I usually use the low gain mode as the majority of my sets are usually IEM earphones. On the left part, the PCM sampling rate LED indicators are arrayed in a perpendicular fashion and it has some levels of sampling rate from the maximum rating of 384kHz down to a standard 44.1kHz. And on the opposite right side, there are DSD sampling rate LED indicators that were arranged in a similar manner below the input mode indicators like optical mode and USB mode. The DSD sampling rates that have LED display status are DSD64, DSD128 and DSD256 which are more than enough as my collection of DSD files are usually in either DSD 64 or DSD128 format. The volume level status indicator depends on the intensity of flashing lights of magenta colour, the more that we increase its amplitude, the more intensity of blinking lights it occurs. Then below the volume level indicator, there's the power mode indicator that was situated there.



The large knob is used for volume adjustment depending on the loudness level of your choosing. As for click commands that I have mentioned a while ago, a single click is for play/pause, double-clicks for mute/unmute and a long press for 3 seconds on power on/off. It should be noted that command clicks won't work on optical signal connection mode except for the long press one.



At the rear part of this device, there's the power/USB Type-C input port for USB connectivity for PCs, laptops, TVs and other devices and it is also used as a pre-amps pairing it with speakers or amplifiers. The other ports are optical input for TOSLINK-supported devices in which my majority of testing is conducted in this manner and an 3.5mm AUX port for analogue signal output.



And in the front part, there are two types of audio output interfaces that were implemented here, the standard 3.5mm single ended headphone jack and a 4.4mm balanced headphone jack. The 3.5mm headphone jack power output rating is quite powerful and robust as it is capable of delivering a 280mW@32 ohms at high gain mode while the 4.4mm balanced output can deliver up to 1.62W@32 ohms in high gain mode.



Regarding its internal parts, FOSI AUDIO did implement a flagship ESS reference DAC Chip, The ES9038Q2M which is known for its reliability and high performance. The ES9038Q2M is a capable 2-channel stereo DAC with its vaunted proprietary 32-bit Hyperstream architecture with clock jitter eliminator which enables it to deliver a clear, distortion-free audio signal output with a less demanding power consumption. Aside from a high performance DAC, it uses a separate headphone op/amp, SGMicro SGM8262 which is a high speed operation amplifier with low noise and voltage feedback functionality which gives a substantial load of output swing for better linearity and improving its dynamic range performance.



As for product packaging, like all FOSI AUDIO products, the device and with other contents was put in a protective styrofoam in a rather minimalist packaging box.



Here are the contents inside of FOSI AUDIO packaging box:

• FOSI AUDIO SK02 desktop headphone amplifier
• A long Type-C to Type-C USB cable
• Instruction manual

This desktop amplifier will be normally used for decoding audio codecs from PCs, laptops and other multi-media consoles if you use its type-C input as its connection. But if you are using this in your smartphone like a typical USB DAC/amp dongle, it will definitely won't work at all as this device needs a required input voltage of DC 5 volts just to power this one. The majority of the duration of its testing phase of this device will be in optical mode in which I will connect it to QUESTYLE QP2R DAP which has TOSLINK support for analogue connectivity, so it will serve as an amplifier. I will also share some insights on how this device will perform as a desktop DAC when I tested it on my mate’s laptop.



Furthermore, to conduct a test, I will use a variety of IEMs in my collection from warmish-neutral LETSHUOER CADENZA 12, SEE AUDIO BRAVERY RED and BQEYZ WIND, a DF-neutral like LETSHUOER EJ07, reference-neutral sets like KINERA IDUN GOLDEN, HIBY CRYSTAL 6 II and LETSHUOER EJ09, a mild U-shaped AFUL PERFORMER 8, A warm sounding ORIVETI OD200 and lastly, some balanced-neutral sets like LETSHUOER EJ07M, AFUL MAGICONE and BQEYZ WINTER.

The sound impression that this device is able to deliver is a reference-neutral sound which has more emphasis on midrange and high frequencies to give that bright, crisp and detailed sound quality.




LOWS/BASS:

The device is able to deliver a precise, rumbly and incisive sound with a very little colouration as it maintains a tidy bass response that is well-segregated from other frequencies.

While it maintains a sub-bass presence just to exhibit if a certain track requires more reverberation, its mid-bass appears to be quite linear but it is enough to give an ample amount of texture for bass-focus instruments and bass-baritones vocals.


MIDRANGE:

My initial impression on how the midrange presentation is transparent, neutral and energetic as it gives more articulation, clarity and silvery vocals, mainly on female types and some instruments.

If I paired it with warmer sounding IEMs, it just gives more clarity on male vocals to sound more expressive and some detail on its vocal ends in which tenors and countertenors will sound more brassy and musky respectively. As I mentioned that female vocals will benefited more on this one especially if I pair it with reference-neutral tuning sets as it adds more emotive and fiery sound on mezzo-sopranos while the energetic nature of this device will give a more gleaming and shimmering on sopranos as it sounds so open that it project its highest note range.

On instruments, it adds some richness and crispness tones of some instruments particularly on some strings, percussions and woodwinds as it still sounds natural but more detailed on its timbre. Once again, if I pair it with warmer or balanced-neutral sounding sets, it has a very little to none amount of colouration on some brass and percussives that will sound marginally negligible into my ears at all.


HIGHS/TREBLE:

Treble response of this one is definitely bright with a lot of detail, sparkling and quite well-extended.

Pairing it with reference-neutral sets which have more emphasis on upper-mids up to the brilliance part of the treble region will be more accentuated so that it will have more definition and clarity.


OVERALL TECHNICAL PERFORMANCE:

This device is quite analytical in that aspect as it will deliver a more resolving sound in a clean pitch black sonic background. It is able to project a rather spacious stereo imaging with a well-layered of frequency and dynamic tones in a sonic canvas. Separation of instruments is quite remarkable as it has a good gap and spacing on each element.

Resolution capabilities of this one is outstanding as it is able to deliver well-textured macro-dynamics while its micro-dynamics is exceptional as it has a sharper definition on extracting nuances, subtleties and intricacies of note textures from an audio source.


There will be no peer comparisons section as I don't have any desktop amplifier aside from this unit. But I did test some iFi like Zens, S.M.S.L. desktop amps in which I forget its model and Chord Mojo and I find them more coloured sounding due to their warm and analogue-ish nature.


To sum up my assessment in regards to this product, FOSI AUDIO continues to impress me even more that this device performs beyond my expectation. So what are my takes about this one, first one is the desktop amplifier is quite solid for its build construction while maintaining a balanced weight. Second one is pricing which is quite affordable and reasonable for its performance. Third one is its overall sound quality as it has a robust and powerful amplification on its power output while maintaining a neutral and analytical sound. And last but not the least, was its versatility that I can even use it in both modern and analogue audio desktop gears. To whom will I recommend this one? My best answer is for audio enthusiasts who keep pursuing more high-fidelity audio with a very competent technical performance but their budget is rather limited.

FOSI AUDIO SK02 is now available at HIFIGO, ALIEXPRESS and AMAZON. Check out my unaffiliated links that I've provided below:


★★FOSI AUDIO SK02 - HIFIGO★★

★★FOSI AUDIO SK02 - ALIEXPRESS★★

★★FOSI AUDIO SK02 - AMAZON (US)★★

★★FOSI AUDIO SK02 - AMAZON (JP)★★


For my previous review of a FOSI AUDIO product, click the link below to know more about the company.

■ FOSI AUDIO MC101





SPECIFICATION:

Some Tracks Tested: ( * = 16-bit FLAC, ** = 24-bit FLAC, *'* = MQA, '*' = DSD, *'= .WAV)

Alison Krauss -When You Say Nothing At All *
Jade Wiedlin - Blue Kiss**
Led Zeppelin - When The Levee Breaks **
Mountain - Mississippi Queen *
Queen - Killer Queen **
Guns N' Roses - Patience *'*
Eric Clapton - Tears in Heaven '*'
Sergio Mendes- Never Gonna Let You Go '*'
Pearl Jam - Daughter **
Roselia - Hidamari Rhodonite *
Assassin - Fight (To Stop The Tyranny)*
Celtic Frost- Visual Aggression *
New Order - Blue Monday *
The Corrs- What Can I do (unplugged version) *
Jimi Hendrix Experience - Voodoo Child *
The Madness- Buggy Trousers *
Metallica - Motorbreath **
Mariah Carey- Always Be My Baby *
Destiny's Child - Say My Name *
Malice Mizer- Au Revoir *
Mozart - Lacrimosa *
New York Philharmonic Orchestra - Dvorak- Symphony 9 " From the New World." *
Eva Cassidy - Fields of Gold (Sting cover)*
Michael Jackson - Give In To Me *
Exciter - Violence and Force *
Diana Krall - Stop This World **
Debbie Gibson - Foolish Beat *'*
The Sisters of Mercy – Lucretia My Reflection**
Suzanne Vega – Luka **
Lauren Christy – Steep *
Ottoman Mehter - Hucum Marsi *
Diana Damrau - Mozart: Die Zauberflöte*



P.S.

I am not affiliated to FOSI AUDIO nor receive any monetary incentives and financial gains as they provide me a review unit for an exchange of factual and sincere feedback from yours truly.

Once again, I would like to send my gratitude to HIFIGO especially to MS. YUMU SONG and MS. LVY YAN for providing this review unit. I truly appreciate their generosity and trust towards me and other reviewers.

Disclaimer:​

Good morning, readers! In this review, we will analyze Fosi Audio’s latest product. I thank Hifigo, who, together with Fosi Audio, sent me this Fosi SK02 unit to review. I needed something more powerful and this big dongle/AMP has a lot of power.

By now, the quantity of Dongles in my possession has reached a considerable amount. I don’t consider myself a foreigner but hopefully you like my review and find it useful.



The review, as always, will be completely unbiased and uninfluenced.


I would like to remind you that I am just a person who enjoys trying out new items and listening to a lot of music; I am not an expert.


My opinions are obviously subjective.

Tech Specs:​

• Dac: ES9038Q2M
• Op-AMP: SGM8262
• Input USB-C, OPT
• Output: 3.5/4.4mm Headphone
• Out: 3.5mm AUX/OPT
• Headphone Output Power
• 3.5mm PO Low Gain: 90 mW at 32 ohm High Gain: 280 mW @ 32 ohm
• 4.4mm BAL Low Gain: 350 mW at 32 ohm High Gain: 1100 mW @ 32 ohm
• SNR 3.5mm PO Low Gain: 116dB / High Gain: 120 dB
• SNR: 4.4mm BAL Low Gain: 110dB / High Gain: 115 dB
• Distortion ≤0.001% @ 1 kHz
• Noise Floor 3.5mm PO 3.7μν / 4.4mm BAL 12μν
• Crosstalk 3.5mm PO Low Gain: 128dB / High Gain: 137 dB
• 4.4mm BAL Low Gain: 112dB / High Gain: 110 dB
• Frequency Response: 20Hz-20kHz (+0.02 dB)
• Impedance: 16-300 Ohm
• Input Voltage: DC 5V
• Final Price: Around 99 USD (not confirmed)
• Official Fosi Site

Packaging:​

The box is very simple; I’m not even sure that it is the final packaging of the product, as it was sent to me before the end of the Kickstarter. As you can see, it is not tailor-made. Inside, we find the Fosi Audio SK02, the cable with an integrated USB A and Type C adapter (a magnificent accessory), and the manual.


I don’t know the final price yet but theoretically it should be under 100 USD, I think the set of accessories is correct.

Build quality/First impressions:​

Even before opening the package, you can feel its weight. It is certainly not a dongle. Opening the box, its size is immediately apparent; the body is entirely made of aluminum alloy, painted black in a matte finish. The volume knob is also a solid block of aluminum. The peculiarity is that it runs infinitely and allows precise volume adjustment (it has a memory of the settings). The knob also has the function of being pressed and is used to mute, play, or pause.


On the front, we have 2 more buttons, one for the gain and the other for the input mode.


As you can see, the front panel is full of LEDs that indicate the gain. the sampling rate, the input, the power status, and even the volume (or power) level.


In fact, next to the audio/speaker symbol, there is a purple and blue LED that indicates the right and left channels and lights up when the power demand becomes important. Obviously, it lights up to the rhythm of the music. Here, it would have been nice to see two series of LEDs with the musical spectrum, perhaps in the next product.


On the front, we have the two outputs, 3.5mm and 4.4mm balanced, both very powerful.


In the back, we have double input, optical and USB, but also an AUX output if for example, you wanted to use an AUX to RCA cable to connect a speaker amplifier. This output also has optical functionality but its operation is not explained very well, You need a 3.5mm optic cable and in my opinion, it always acts as an audio output so you can connect it to a home theater or a soundbar.


However, it is an extremely versatile product and despite its size, we can also consider it portable as it does not require external or extra power supplies.


Qualitatively speaking, the construction is well taken care of and the assembly is free of defects.

Power:​

In terms of power, considering that it does not require an external power supply, it is a little monster. On the 3.5mm output, we have 280 mW at 32 ohms, which I assume is per channel, This is because, compared to the FiiO Ka11, the volume is much higher. I connected the Hifiman Deva Pro to it with only 18 ohms and it is impossible to reach the maximum volume. The power is sufficient for most headphones and IEMs already on SE output.


On the balanced output, we have 1100 mw at 32 ohm, which I would say are per channel (I have to check with Fosi) but they could easily be the summed values. But seeing the power in the SE of the FiiO KA11, I don’t think it can develop less power. Also because the volume is significantly higher.


Needless to say, it has no difficulty with any IEM or headphones. I don’t have anything with extremely high impedance but I will soon be looking for something with at least 300 ohms.

3.5MM​

For the moment, the heaviest test I can do on a 3.5mm output is the EPZ x Tipsy Star One 64 ohm + adapter with 75 ohm impedance.


I can tell you with certainty that it is not affected in the slightest. Obviously, I have to turn the volume up more but it is still not possible for me to reach the maximum volume. I don’t think you would have any problems with 300-ohm headphones as long as they have good sensitivity.


The Hifiman Deva Pro on 3.5mm seems connected to a balanced output (they also have an impedance of only 18 ohm).

4.4MM​

On balanced 4.4mm output, I have tested all the planars in my possession. As far as IEMs are concerned, it doesn’t have any kind of problem. The KZ PR2 V2, which is the least easy to drive, will likely explode if I try to reach maximum volume. The driver can’t even keep up with the power. As for Hidizs MP145, Letshuoer S12 Pro & S15 and Kefine Klanar, they are managed without any kind of problem.


The Hifiman He400Ses, on the other hand, definitely benefits from the extra amplification. The driver acquires dynamics that I don’t notice with other balanced outputs, including improved soundstage and bass with greater impact.

AUX OUT:​

Given the somewhat particular functioning of this AUX, I asked Fosi for clarification.


I noticed that this output is also amplified and the volume is always controlled via the knob. Theoretically, I would have expected a classic AUX output like I have on my FX AUDIO DAC X6 that I connected to my speaker amplifier. Connecting two amplifiers in cascade, as my colleague Sean pointed out, is not a big deal. Practically, we could also connect headphones to the rear audio output. Now it remains to be understood whether it can also be used at the same time (I doubt it). Furthermore, it is also an optical output and this works normally; we can connect a home theater or any audio system to it.


Update from Fosi Audio:


The rear output has very low amplification and can be used together with the balanced output without problems. I would say that in this case, you can use the output on the back to connect it to a speaker amplifier without any problems. I personally won’t use it that way, as I already have another DAC. The Fosi is extremely convenient for me for headphones and IEMs.

Test/Sound Signature:​

Like all the DACs that use the same chip in my possession, the Fosi SK02 is also characterized by a bright sound. It’s not the brightest but it definitely doesn’t have warm undertones, in fact, if a headphone/IEM is warm, it tends to make it more balanced. You may or may not like this feature but personally, I don’t experience any kind of problem, on the contrary, it doesn’t place an emphasis on the low range like some Cirrus logics. However, in the case of the Hifiman He400Se, the greater amplification gave body to the bass.


So I presume synergy also comes into play, even if it is rare and in some cases, the performances may differ from expectations.

Even the Tanchjim Zeros connected to it demonstrate a certain amount of bass despite being bright.

As far as I’m concerned, the Fosi SK02 will remain on my desk as a neutral, bright, and powerful reference. For a little more analytical and critical listening, it seems suitable to me.

The Fosi Sk02 works differently depending on what I plug it into. On my iMac, I can play-pause tracks, while on my smartphone, I can only mute them. On the iMac, the volume can only be managed by the SK02, while on a smartphone, you have double adjustments. In both cases, it works perfectly, demonstrating high performance even from type C.

Fast Comparison:​

vs iBasso DC04 Pro

iBasso DC04Pro
iBasso DC04pro has something more than the others; they may be small things but although the chip is identical to that of the Moondrop Dawn Pro, the OP-Amp department is evidently more refined. I don’t think the price difference is just a matter of brand but to be sure, they would need a teardown. It comes across as more musical and refined, with a soundstage that sometimes seems wider. The Fosi SK02 is brighter and, in any case, much more powerful and practical for desktop use.


vs Hidizs S9 PRO Plus

Side
Hidizs S9 Pro Plus has its own sound coloring in the DACs. There are those who might think that it is a negative factor but the difference is that even if it doesn’t upset you on some IEMs, it is more noticeable. The sound is slightly warmer and focused on the vocals. It somehow makes even trebles smoother without losing detail.


vs Moondrop Dawn Pro

First look Moondrop Dawn Pro
This is an excellent entry-level DAC that allows everyone to get close to the balanced output. For the asking price, the Moondrop Dawn Pro is definitely the right choice. In terms of sound, it is warmer than the Fosi SK02 but not too much.


Vs Fosi K5 Pro

Fosi Audio K5 Pro
I’ve reviewed it elsewhere so I’ll put a friend’s review in the link. The Fosi K5 Pro is certainly a much less serious DAC, the difference is noticeable but it has the convenience of being able to adjust the highs and lows. This feature is great and would have been very useful on the SK02.

Who do I recommend this DAC to?​

Like all the DACs that use the same chip in my possession, this one is also characterized by a bright sound. It’s not the brightest but it definitely doesn’t have warm undertones; in fact, if a headphone/IEM is warm, it tends to make it more balanced. You may or may not like this feature but personally, I don’t experience any kind of problem; on the contrary, it doesn’t place an emphasis on the low range like some Cirrus logics. However, in the case of the Hifiman He400Se, the greater amplification gave body to the bass.


So I presume synergy also comes into play, even if it is rare and in some cases, the performances may differ from expectations.

Even the Tanchjim Zero connected to it demonstrates a certain amount of bass despite being bright.

As far as I’m concerned, the Fosi SK02 will remain on my desk as a neutral, bright, and powerful reference. For a little more analytical and critical listening, it seems suitable to me.

Where to buy?​

HiFiGo

Aliexpress

Amazon US

Amazon JP

Fosi Audio Official Site + 15% Limited Coupon FASKMKT15

The Fosi SK02 shows itself as a pretty compact desktop DAC/AMP, ideal for space conscious users. But I can tell you that its desktop aesthetic offers remarkable versatility and it makes it suitable for mobile use as well!

The metal housing feels like a metal brick, and it fits greatly into any desktop setup or on the go powerful audio rig and its is available for $99.

Disclaimer:
I have to note that this review unit of the Fosi SK02 was provided to me directly by Fosi Audio. I appreciate their support but I want to keep it clear that all opinions expressed in this review are my own and based on my independent testing and experience! I want to keep my reviews unbiased and transparent as much as possible and offer an honest perspective for potential buyers.

Unboxing
The Fosi SK02 arrived in a minimalist box with the phrase 'HiFi Made Fun' written on it, and it sets the tone for what was inside. Upon opening the Fosi SK02 box, the sleek metal device was revealed and it was concealed in protective foam.

Additionally, I found a user manual and a USB Type C to Type C cable with a USB Type A to Type C adapter which makes it suitable for various devices!


Design and Build Quality
The SK02's design stands out from the crowd, taking minimal desk space and making it easy to carry with you when you are on the go. Although you may not be able to put it in your pocket... It is still small enough to easily fit in your bag. I personally love its visual appearance, it may not appeal to everyone's aesthetic preferences...

The large volume knob doubles as a power button and play/pause control and it offers a convenient operation. However, it has a very lightweight feel and I can easily make accidental adjustments... Additionally, the volume level light indicator is very inconvenient to use, as it shows the volume level by its changing flashing brightness, and the absence of an LCD display makes checking volume levels slightly harder.


Technical Specifications
DAC Chip: ESS Sabre ES9038Q2M
Operational Amplifier: SGM8262
Maximum Sample Rate: PCM 384kHz/32bit, DSD256
Input: USB Type-C, SPDIF (shared)
Output: 3.5mm single-ended, 4.4mm balanced (high gain 32Ω: 280mW/3.5mm, 1100mW/4.4mm / low gain 32Ω: 90mW/3.5mm, 350mW/4.4mm)
SNR: 3.5mm – Low Gain 116dB / High Gain 120dB. 4.4mm – Low Gain 110dB / High Gain 115dB
Distortion: ≤0.001% @1kHz
Noise Floor: 3.5mm – 3.7μV / 4.4mm – 12μV
Crosstalk: 3.5mm – Low Gain 128dB / High Gain 137dB. 4.4mm – Low Gain 112dB / High Gain 110dB
Frequency response: 20Hz-20kHz (±0.02dB)
Headphone impedance: 16-300Ω
Input voltage: DC 5V
Hardware Controls: Power, volume, high/low gain switching, input switching
Dimensions: 130mm (H) x 62mm (W) x 23mm (D)
Weight: 340g

Versatility and Connectivity
I think that the Fosi SK02 really stands out for how versatile it is and all the different ways you can connect it to your audio setup. One of the best features, I noticed immediately is that it can be powered with only my phone and it makes it portable and somewhat possible for carry around and I find this feature very welcome!

The SK02 gives you a few options to connect it to different audio sources and devices. It offers a standard 3.5mm headphone jack, a 4.4mm balanced output and an additional 3.5mm AUX output on the back, which from my testing has lower power output and probably can act as a preamp.

The optical input on the SK02 also gives you the option to connect digital audio sources like PCs, consoles, or TVs. And for me all of this makes the SK02 super versatile and easy to fit into pretty much any audio setup!

On top of that, the Fosi SK02 has an SPDIF output from the back 3.5mm optical output. This dual feature really gives you even more options for connectivity and it lets you use the optical output for digital audio as an "adapter" or the regular AUX output.

so... all in all, the Fosi SK02 is great for its versatility and all the ways you can connect it. Whether you're an audiophile, music lover, or just a casual listener, the SK02 is an awesome audio companion! And what made me really fall in love with it is the fact that It works as a portable headphone amp or as part of a home audio system.



Controls and User Experience
The SK02 prioritizes user convenience with intuitive controls and clear indicators. The volume knob, despite its lightweight feel, offers very precise volume adjustments with big number of volume levels. Additionally, a single button switches between the low and high gain and is shown by LED lights. It gives users the option to optimize the setup to their headphone/IEM requirements.

Further enhancing versatility, the SK02 conveniently allows you to switch between optical and USB input sources at the press of a dedicated button. This flexibility caters to various connection preferences and seamlessly integrates the SK02 into different setups, be it your computer, mobile phone, or a dedicated media source with optical output or even an optical input.

Additionally, there is a sampling rate indicator and it goes from 44.1kHz to 384kHz, and a DSD indicator from 64 to 256. However, the flashing and volume indicator, while attempting to convey loudness levels, may prove distracting and less informative in practice, And I must say... it really annoys me...

Power
The Fosi SK02's multiple output options makes it so it can fit in many audio setups. its 3.5mm single ended output on the front panel delivers 280mW (on high gain) clean and detailed sound. This output provides pretty much enough power to drive most IEMs and headphones efficiently.

In addition to the 3.5mm single ended output, the SK02 also offers a 4.4mm balanced output on the front panel and this one brings 1100mW (on high gain)!. I should note that the balanced output is offering several advantages, which are, improved channel separation, reduced crosstalk and lower distortion compared to single ended connections... It gives a more powerful dynamic and also can drive even more power hungry headphones and even planar headphones.

Furthermore, the SK02 offers a rear 3.5mm AUX output, giving users with added flexibility in their audio setups. While this rear output delivers less power compared to the front 3.5mm output, it still offers sufficient amplification to drive a wide range of IEMs with ease. But in my case, I was using it as s preamp...


Sound Performance
The Fosi SK02 brings a sound signature which more bright and detailed, and showing itself as a more revealing performer. At its core is the ESS Sabre ES9038Q2M DAC chip, which is actually known for its clean and crisp sound delivery... This gives the SK02's its most defining characteristic, which a pronounced mid-treble focus.

This focus gives sparkly sound to cymbals, airy vocals, and great details for string instruments. The SK02 excels at showing micro details and to my taste it is inviting to delve deep into the music with analytical approach! But I should warn you that this focus can become a double edged sword... Harsh recordings or tracks heavy on high frequency content might sound overly bright or even piercing to sensitive ears...

Vocals have their own space, delivered with clarity and precision! Every word carries weight and offering a transparent window into the artist's expression. However, this analytical presentation can come at the cost of the warmth and fullness that you might get with the traditional "musical" midrange... Instruments like guitars and brass instruments may lack the organic body and richness found in warmer amps...

Bass presence keeps itself solid, controlled, and tight and proves a good foundation for the rest of the spectrum. It brings enough punch to satisfy most genres but doesn't overpower the mids and highs. However, bassheads or those seeking a more impactful low end rumble might find it wanting compared to warmer competitors like the Truthear Shio...

But overall, I find the Fosi SK02 great for those analytical listeners who prioritize detail and clarity. It shines with acoustic and classical music, where its ability to unveil intricate details is a strength. However, its bright focus might not be for everyone... Especially those who prefer a warmer, more forgiving sound...


Conclusion
So, after all of this, I can easily say that the Fosi SK02 stands out as a versatile DAC/AMP that transcends its desktop oriented design to offer mobile users a compact and powerful audio solution with the possibility to run only on a single USB! Yes, it has a bright and detailed sound signature, and may not be ideal for bassheads, but its sturdy build quality, and diverse connectivity options makes the SK02 a great option for audiophiles seeking a balance between portability and performance. And while this one can feel a little like a brick... it does little to diminish the overall value as a versatile and capable audio on the go companion for both desktop and mobile use. And lets not forget that all this package is priced at $99... And it makes it a great all arounder for those who want it to do everything on a limited budget!

Fosi Audio takes a giant leap, with their first all-in-one headphone source, with the SK02 Desktop DAC/Headphone Amp.

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If you don't like reading, here's the video version of this review


Build, Aesthetics & Ergonomics

The first thing to note is the all aluminium alloy chassis.
It shares it's fundamental housing design with it's sibling the SK01.

The main human interface is the single full aluminium alloy Multifunctional Knob.
At the far end of the unit are two buttons; a gain toggle and an input Mode toggle between USB and Optical.
The SK02 has a 3.5mm phone out and a balanced 4.4mm out on the front and on the rear you will find USB input for power and digital connection, Optical input and a 3.5mm Aux out.
And finally on the bottom, two flat rubber feet keeps your furniture scratch free.

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Functionality

Aside from the Gain and Input Mode toggle buttons, the Multifunctional Knob is the main way to control this device.
To turn it on and off, simply hold the knob down for 3 seconds.
Clicking the knob once will Play/Pause your music stream and double-clicking will mute the internal DAC.

The knob is the main digital volume control for the internal DAC.
As such it does not take control of your system volume.
The benefit of this is that taking control and lowering system volume can have a small detrimental effect on the sound quality, so this takes that problem out of the equation.

Also this is much more user-friendly for people who deal with multiple sources like me; there will never be a chance of lowering the system volume and forgetting to push it back up to maximum for your other devices.



For analogue fans the digital knob does come with a learning curve.
There is of course no way to know what volume the unit is set to as the knob will spin infinitely in both directions.
In the past few weeks there were a few moments switching between sources and different headphones when the SK02 was pushing out too much volume, so after a few ear-punishing momments I quickly learned to crank the volume all the way, which is just a matter of spinning it a few times anti-clockwise before plugging in a new headphone or listening to music.

At this price point, a volume display would be a lot to ask for, so I'm on the fence about criticizing this too harshly. Either way, there will be a small learning curve for people who have only used analogue controls previously.

The Gain button toggles between:
• Low Gain
- 85mW @32Ω (3.5mm)
- 331mW @32Ω (4.4mm)
• High Gain
- 267mW @32 Ω (3.5mm)
- 1.062 Watts @32 Ω (4.4mm)

The SK02 is designed to be used with more modern headphones from 16-300Ω, so maybe don't go pluggig in your 50 year old AKG studio headphones.
For most users, this range is more than enough and covers almost all bases.



Both the Gain and Input Mode buttons have annotated orange indicator lights.
There are more orange lights for the PCM and DSD sample rate idicators.

It's nice to see Fosi Audio fully embracing this design langauge, as orange accents are also to be found on their other products. It's a small small thing, but this is the kind of attention to detail that I appreciate.

The only exceptions are the power light which is green and above that, the Volume Indicator light which flashes purple depending on the output.
If this light is constant and not flashing, the volume is set extremely high and caution should be taken before plugging in headphones.



If for example you are using the SK02 as a DAC for another, you will use the 3.5mm AUX output to feed that amplifier, however, the SK02 is not a pure DAC, so the most logical next step for most, will be to set the output volume to maximum for the AUX out.
This is a double edged sword, as this is the only way to get the maximum DAC output to another amplifier, but also does not prevent the user from plugging in a headphone and getting a nasty explosive surprise on the front-end.
So if you are planning on frequently using multiple sources, it's a good idea to pay attention to the volume indicator.
I've made a habit of unplugging headphones after every use and always turning the volume down before listening.

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The Sound

Equipped with an ESS 90382QM chip, the SK02 is can handle PCM decoding up to 32 bit at a sample rate of 384 thousand Hz: this unit is able to push out sample rates way beyond human congnitive comprehension and is functionally at the peak of decoding technology.
At no point did I feel that I was getting anything less than a perfectly neutral, high resolution audio experience.
The other benefit of a highly digital device is that on full volume, there was absolutely zero hissing or humming or electrical interferance.
It has one of the absolute cleanest, blackest backgrounds you will ever hear.
From my point of view, this unit guarantees uncontaminated audio.

I tested this with my very sensitive JVC HA-FX1800 IEMs on full volume out of the 4.4mm balanced output and there wasn't even a hint of a hiss.
I even tested it while playing an audio sample of pure silence, just to make sure I was forcing an output.



While the SK02 was not designed as a pure DAC, I have been using it about 50/50, as a headphone amp and as a DAC, with it plugged into my Fosi Audio SK01 Pre-amp and Headphone Amp, for two reasons:
Firstly, it puts out a perfectly clean signal on maximum AUX output, and behaves as a DAC without producing excess heat or consuming huge amounts of power.
Secondly this combination has been a great source and pre-amp for my Stax SRM-313 electrostatic amplifier.
I find that electrostatic amps are generally more sensitive than most to even the tiniest hints of audio/electrical signal contamination, so this is one of the cheapest and most effective ways I can think of to provide a clean, high-fidelity source and good tone control - which many electrostats do require.

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Conclusions

Overall, this little DAC/amp combo leaves little to be desired.
If anything, I think I might be becoming a bit of a digital control convert and evangelist.

If the competent maximum output of 1 Watt on balanced, or the perfectly black background does not convince you, just remember, this thing is practically portable, takes up very little desk space and only requires the supplied 5 Volt USB connection to run.

The only thing I can see that might be missing for some is a 6.3mm socket.
Otherwise, it's just been a joy to use and listen to music with.