FOSI AUDIO SK02: Well-Rounded, Vigorous and Meticulously Technical Performer
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 - 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.
SPECIFICATION:
| 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 |
PROS:
● Solidly-build, all-metal alloy chassis desktop amplifier.
● For its chunky size, it has a balanced weight on it that make more manageable to carry it around.
● Versatilty in terms of power input modes
● Precise and smooth operation on its multifunctional knob for more finer and granular volume control and its clicky response is quite snappy and tactile.
● Aside from a standard 3.5mm single ended headphone jack, it also has a 4.4mm balanced headphone jack which makes its audio interfaces more flexible to used.
● Manual gain modes.
● Very robust and powerful amplification on both headphone outputs.
● This device will be able to drive some of the stubborn high impedance cans that requires more power.
● Implementation of high performance and reliable ESS DAC
● LED indicators for gain mode, input mode, PCM sampling rate, DSD sampling rate, volume ane power.
● Sampling rate up to 384kHz at PCM.
● DSD support up to DSD256.
● Analytical, neutral sounding.
● Highly competent on its technical performance.
● Clean, pitch-black sonic background.
CONS:
● Looking for warmer, smooth and analogue-ish kind of sound?Then this is not the desktop amplifier that you are looking for.
● Let's be honest on this one, it is still quite bulky.
● Lack of support on system-wide software volume control on music apps.
● Analytical sounds might be too boring in a long run to some listener.
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.
Great review sir👏
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