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:
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.
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.
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
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.
9/10
Pros:
- Build Quality
- Metal body
- Powerhouse
- Doesn’t need external power
- Neutral (hint of warmth), analytical
- Infinite volume knob with Play/Pause function on PC
- Gain and Mode Button
- Many LEDs
- Total Independent volume on my iMac
- Independent volume + volume on Smartphone
- Can work connected with your smartphone (external power not needed)
- Optical input and output
- Type C cable with USB adapter
Cons:
- Chunky big boy
- Maybe too bright for someone (not in my opinion)
- When it is turned off, it is still warm (Probably draws power)
Where to buy?
Fosi Audio Official Site + 15% Limited Coupon FASKMKT15