FiiO KA3 vs Hidizs SD2

Short answer

More power: the FiiO KA3, with 130 mW into 32 Ω; the Hidizs SD2 has 70 mW. The FiiO KA3 drives 9 headphones to 100 dB that the Hidizs SD2 cannot (HiFiMAN Susvara, Moondrop COSMO, Moondrop PARA 2, 6 more).
Hiss with sensitive IEMs: cannot be compared — the maker of the Hidizs SD2 publishes no noise figure.
Price: the FiiO KA3 costs $29 more; what that buys on these numbers is set out further down, under What the price difference buys.

Both are dongles, $79 against $50.

The FiiO KA3 reaches 100 dB on 565 of the 567 models here, the Hidizs SD2 on 556.

Side by side

Every published figure, next to each other

Specification	FiiO KA3	Hidizs SD2
Power into 32Ω	130 mW	70 mW
Power into 150Ω	28 mW	15 mW
Power into 300Ω	14 mW	7.5 mW
Power into 600Ω	7.0 mW	3.7 mW
Output impedance	0.5 Ω	not published
Output noise	1.7 µV	not published
Price	$79	$50
Headphones it reaches 100 dB on out of 567	565	556

Not published means the maker leaves it out, so that axis cannot be compared.

Balanced output

The 4.4 mm or XLR socket, rated on its own

Balanced	FiiO KA3	Hidizs SD2
Socket	4.4mm	no separate rating
Power into 32Ω	240 mW	—
Power into 300Ω	56 mW	—
Output impedance	0.7 Ω	—
Output noise	2.9 µV	—
Headphones it reaches 100 dB on out of 567	565	—

Only the FiiO KA3 has a separate balanced rating from its maker; through it, it reaches 100 dB on 565 of the 567 models here. The Hidizs SD2 may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it.

How solid these numbers are

Where each power figure comes from

Load	FiiO KA3	Hidizs SD2
32 Ω	Published	Published
150 Ω	Derived	Derived
300 Ω	Published	Derived
600 Ω	Published	Derived

Both makers publish a power rating. FiiO KA3 publishes at 32 Ω, at 300 Ω and at 600 Ω; Hidizs SD2 at 32 Ω. The other rows are worked out from those.

So the two columns are not equally firm row by row: at 300 Ω and at 600 Ω only the FiiO KA3 figure is the maker’s own. On those rows the derived number is the one to doubt first.

What the labels mean.

What separates them

The headphones that tell them apart

9 headphones reach 100 dB on the FiiO KA3 but not on the Hidizs SD2 — HiFiMAN Susvara, Moondrop COSMO, Moondrop PARA 2, 6 more.

556 of the 567 models here reach 100 dB on both.

On real headphones

Headroom and hiss on 8 models, both sources

Headroom is at a 100 dB SPL peak.

The widest gap on the list is the Campfire Audio Andromeda 2020: FiiO KA3 has +12 dB of headroom there against +7 dB. 5 dB is about 3.4 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Hidizs SD2 because that maker publishes no output noise figure.

Headphone	Impedance	Needs	FiiO KA3 headroom	Hidizs SD2 headroom	FiiO KA3 hiss	Hidizs SD2 hiss
Shure SE846	9 Ω	0.04 mW	+32 dB	+27 dB	19 dB	not published
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+12 dB	+7 dB	-1 dB	not published
Audeze LCD-2 Classic	70 Ω	0.79 mW	+19 dB	+16 dB	-3 dB	not published
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+14 dB	+12 dB	-7 dB	not published
HiFiMAN HE400se	25 Ω	7.9 mW	+12 dB	+8 dB	-8 dB	not published
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+8 dB	+5 dB	-14 dB	not published
Sennheiser HD 600	300 Ω	6.6 mW	+3 dB	+1 dB	-18 dB	not published
HiFiMAN Susvara	60 Ω	50 mW	+1 dB	-1 dB	-20 dB	not published

What the price difference buys

The gap in dollars, against the gap in numbers

The FiiO KA3 costs $29 more than the Hidizs SD2. Out of the 567 models here, that difference buys 9 more models driven to 100 dB.

Nothing runs the other way: there is no axis here on which the cheaper of the two does better.

Only published figures count here; blank axes are counted separately.

Each in full: FiiO KA3 and Hidizs SD2.