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Fosi Audio SK02 DAC & HP Amp Review

Rate this DAC & HP Amp: (votes are based on data in review and not necessarily personal ownership)

  • 1. Poor (headless panther)

    Votes: 6 2.8%
  • 2. Not terrible (postman panther)

    Votes: 31 14.7%
  • 3. Fine (happy panther)

    Votes: 121 57.3%
  • 4. Great (golfing panther)

    Votes: 53 25.1%

  • Total voters
    211

amirm

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This is a review, listening tests, and detailed measurements of Fosi Audio SK02 USB powered DAC and balanced headphone amplifier. It was sent to me by the company and costs US $99.99 (€99.00).
Fosi Audio SK02 Desktop DAC Headphone Amp balanced review.jpg

The SK02 is excellently designed. Having it horizontal gives comfortable access to the rotary volume control. I was going to complain about it not showing the current level but then noticed an LED which blinks with music signal and becomes brighter at higher volumes. Brilliant! The rest of the LEDs provide the exact kind of information you want to know about the status of the device and the format of the incoming signal. Again, wonderful. The gain button is right there to nicely control that setting. And mode selects between Toslink optical and USB-C inputs:

Fosi Audio SK02 Desktop DAC Headphone Amp balanced usb powered review.jpg


This is as ideal of a design as one can imagine for a compact dac and headphone amplifier.

Fosi Audio SK02 DAC Measurements
I started with balanced HP output, setting it to 4 volts using the volume control (high gain):

Fosi Audio SK02 Desktop DAC Headphone Amp balanced measurement.png

This nicely lands the SK02 in the middle of our "competent" rating of all DACs ever tested:
best budget desktop dac and hp amp review.png

best budget desktop dac and hp amp zoomed review.png


Unbalanced 3.5mm turns in similar performance:
Fosi Audio SK02 Desktop DAC Headphone Amp unbalanced measurement.png


Company spec is 106 dB which is essentially what I am measuring.

Noise performance is excellent for class:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced dynamic range measurement.png


Jitter test shows some interference but they are below audibility:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced Jitter measurement.png


Linearity is near perfect:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced linearity measurement.png


IMD test shows the class sign of "ESS DAC IMD hump:"
Fosi Audio SK02 Desktop DAC Headphone Amp balanced IMD Distortion measurement.png

I put most of the blame for this on ESS for not issuing a bulletin on how to fix this, leaving every company to have to fix it themselves.

The filter has good response in audible band but not enough attenuation in ultrasonics:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced Filter measurement.png


This naturally hurts the wideband THD+N measurement:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced THD vs Frequency measurement.png


If your player can upsample to higher frequencies, you may want to use it (set it to 192 kHz).

Multitone performance is again excellent for class:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced Multitone measurement.png

Even the worst case intermodulation is at or below threshold of audibility.

Fosi Audio SK02 Headphone Amplifier Measurements
We have surprising amount of power for a USB powered device:
Fosi Audio SK02 Desktop DAC Headphone Amp Unbalanced 300 ohm measurement.png

Note that the gain switch simply rescales the volume control and hence, won't get as loud. It therefore has no effect on actual performance. So I focused on high gain for the next tests:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced power 32 ohm measurement.png

We see that a lot more power is delivered with high gain. And that unbalanced has lower noise floor so use that for IEMs which don't need a lot of power anyway.

Sweeping impedances we see that the ultimate limit of USB power kicks in:
Fosi Audio SK02 Desktop DAC Headphone Amp balanced power vs impedance measurement.png


Unfortunately output impedance is non-zero so be mindful of that with headphones that have variable impedance vs frequency.

Fosi Audio SK02 Listening Tests
I started my testing with Dan Clark E3 which is low impedance and difficult to drive. I was pleased that the SK02 could drive it to reasonable levels with very nice fidelity using balanced output in high gain. Cranking it all the way up did cause it to shot down however.

I switched to Sennheiser HD-650 which in high impedance could be pushed to any level you wanted. The sound was beautiful with all the detail, bass impact, etc. that you would (almost) want. I also tested it with unbalanced output and while max volume was lower, it was still enough for everyday use.

Conclusions
Fosi innovates in user interface in this form factor producing best in class functionality and usability. Objective performance ranges from excellent to areas that need addressing. Subjective testing results were quite positive for this class. It is not everyday that I get excited about "yet another dac and amp" but I am that way about SK02. Given how responsive company is to user input, I am hopeful that the next revision will iron out the weaker points and produce even better performance.

I am going to recommend the Fosi Audio S02 based on its practical performance and usability at very reasonable cost.

------------
As always, questions, comments, recommendations, etc. are welcome.

Any donations are much appreciated using: https://www.audiosciencereview.com/forum/index.php?threads/how-to-support-audio-science-review.8150/
 

Mikig

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Fosi is increasingly getting us used to products that are cute, functional, perform well and are reasonably priced.
In a word "concrete".
He's only missing one thing: the orange wheel!!

Thanks Amirm as always for the review!
 

Leiker535

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Local reviewer here ran a noise signal through the little DAC and got worrisome results. I don't know how to properly interpret it, maybe it is due to the rising THD up the high frequencies shown here as well?

1710285010888.png

Other than that, the high gain power max was 40% behind spec, but should be fine for class and price. In this sense, I must admit, this device's feature set astonishes me for the price. Not mentioned here in the review is it's DDC capability: it's aux out doubles as spdif out. Maybe you could measure it too @amirm ?
 

phoenixdogfan

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Pair this with HiFiMan HE 400, or Senn HD 650, or Aune AR 5000 and it's possible to create a very high end starter set for less than $500.

For some real giggles, buy a pair of binaural mics, add HeSuVi to your PC, and create a 7.1 Home Theater over headphones for streaming Netflix and Amazon Prime.
 

Fosi Audio

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We are deeply grateful to Amir for the comprehensive measurements, as well as for the encouragement towards us. We'll keep responsive to user input and make efforts to bring more nice audio gear to audiophiles. :D

And here is a dedicated 15% discount promo code for all ASR members: FASKASR15
 

Adaboy4z

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I saw a couple of reviews on You tube and though nice form factor to sit next to the PC monitor.
 

mc.god

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Nice device and review, thank you. Can we know noise at 50 mV?
Anyway voted fine, it would be great with lower output impedance.
 
OP
amirm

amirm

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Since you have Roon it would be nice if you could show the measurable improvement this makes
I partially showed that in the measurement by setting it to 96 kHz.
 
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mctron

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I've seen much better performing DACs receiving the headless panther because of the price. Can't understand why the price makes this one a great DAC. A cheap DAC I agree, but then I've seen cheaper dongle dacs performing better here.
I would imagine the panther covers all the factors at once - price, performance, build quality, usability, etc not just one ie your first example price or your other example performance
 

Beershaun

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I've seen much better performing DACs receiving the headless panther because of the price. Can't understand why the price makes this one a great DAC. A cheap DAC I agree, but then I've seen cheaper dongle dacs performing better here.
It's a heck of a value for a DAC+amp. Good performance and power and not broken anywhere. That gets a "very good" in my book.
 

Egoist

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It's a heck of a value for a DAC+amp. Good performance and power and not broken anywhere. That gets a "very good" in my book.
That filter implementation hurts my eyes. The unbalanced linearity, the (very pronounced) ESS hump and the messy jitter performance do the rest. A Moondrop Dawn or similar dongle DAC have better objective performance for less cost. Two high end DACs reviewed recently blow this DAC out of the water and both got an headless panther. There are much better options for the price, if that's what's being evaluated here.
 

Kimbrough Xu

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Quite a difference to their last model in this line, a decent improvement;

index.php


Cheers for the testing Amir.


JSmith
I really like the use interface that are on the top of the SK02, it is much more convenient to use on desk than most of the other products that are on the front panel. Maybe we can ask more from fosi, so that they can develop higher performance and better prodcut yet still affeordable.
 
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amirm

amirm

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A Moondrop Dawn or similar dongle DAC have better objective performance for less cost.
A dongle is not competition for this desktop device. The volume control and form factor blow them out of the water as far as usability. Have you tried to adjust the volume on those dongles? Also, I have yet to test a dongle with clean response. They all have jitter issues, etc.
 
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