Fosi Audio SK02: power output and what it will drive

The Fosi Audio SK02 is a desktop amplifier at $100. It delivers 190 mW into 32Ω and 20 mW into 300Ω, which ranks it 163 of 280 for raw power among the sources in this database.

Measured at 100 dB SPL it has comfortable headroom on 521 of the 567 dynamic and planar headphones catalogued here, enough but not generous on 38, only marginal on 5 and not enough power for 3. Power is published at 32Ω; the rest of the table is derived from those figures. Output impedance is not published. Output noise is not published, so the hiss estimate cannot be run.

The manufacturer publishes 190 mW into 32Ω. The rest of the table is worked out from those.

The balanced output is rated separately: 755 mW into 32Ω through the 4.4mm jack.

Derived rows hold output voltage steady, as an amplifier does (method).

The noise figure above is the maker’s own, but it is not in the specification table. Fosi Audio prints it in the product description: “a low noise floor of only 3.7μV”. Nothing is calculated here — the microvolts are theirs. What the sentence does not say is which output it describes, or which gain setting, and the table beside it distinguishes both. It does agree with their own table. The same page prints a 116 dB signal-to-noise ratio for the 3.5 mm output at low gain, and 190 mW into 32 ohms for that output, which is 2.466 volts; 2.466 volts against a 116 dB ratio is 3.90 microvolts, half a decibel from the 3.7 in the sentence. That is the reading used here: the single-ended output at low gain.

Source: fosiaudio.com.

Easiest to hardest to drive, with headroom at a 100 dB SPL peak.

At 3.7 µV of output noise, here is where that noise lands in the five most revealing in-ears in the database.

This one hisses. With the most sensitive in-ears in the database its own noise lands around 32 dB SPL, which you will hear between tracks and in quiet passages.

The manufacturer does not publish an output impedance for this source. Without it, nothing here can say how this source will behave with a multi-driver in-ear.

With a measured figure, the checker works out the consequence.

Of the 280 sources here, 5 do everything the Fosi Audio SK02 does as a headphone output: reach 100 dB on every headphone it reaches and stay under the audible-hiss threshold wherever it does. The cheapest of them is the FiiO KA11 at $29, against this one’s $100 — $71 less, and a USB dongle rather than a desktop amplifier.

The cheaper one also publishes an output impedance, which the Fosi Audio SK02 does not — so on the paperwork it is ahead, not merely level.

This counts the headphone output only; inputs, converters, the volume control and the build are outside it.

Compared with its closest rivals: vs JDS Labs Atom+ (2nd gen) · vs Schiit Magni Heresy · vs Schiit Magni+ · vs SMSL HO100 · vs Topping L30 II.

Compare any two or match your own headphones. Every Fosi Audio source here.