FiiO KA5 vs HiBy FC4

Short answer

Power: about the same. The FiiO KA5 has 122 mW into 32 Ω, the HiBy FC4 110 mW (balanced: 265 mW and 340 mW). The FiiO KA5 drives 4 headphones to 100 dB that the HiBy FC4 cannot (Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more).
Hiss with sensitive IEMs: no headphone here hisses audibly on one and not on the other.
Price: the same, $99.

Both are dongles, both at $99.

The FiiO KA5 reaches 100 dB on 565 of the 567 models here, the HiBy FC4 on 561.

Side by side

Every published figure, next to each other

Specification	FiiO KA5	HiBy FC4
Power into 32Ω	122 mW	110 mW
Power into 150Ω	26 mW	23 mW
Power into 300Ω	14 mW	12 mW
Power into 600Ω	6.8 mW	5.9 mW
Output impedance	0.3 Ω	not published
Output noise	1.6 µV	1.7 µV
Price	$99	$99
Headphones it reaches 100 dB on out of 567	565	561

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 KA5	HiBy FC4
Socket	4.4mm	4.4mm
Power into 32Ω	265 mW	340 mW
Power into 300Ω	54 mW	36 mW derived
Output impedance	0.35 Ω	not published
Output noise	1.8 µV	2.2 µV
Headphones it reaches 100 dB on out of 567	565	565

Through the balanced sockets the two are level on the same test: each reaches 100 dB on 565 of the 567 models here. Derived figures are worked out from the loads the maker did publish.

How solid these numbers are

Where each power figure comes from

Load	FiiO KA5	HiBy FC4
32 Ω	Published	Published
150 Ω	Derived	Derived
300 Ω	Published	Derived
600 Ω	Derived	Derived

Both makers publish a power rating. FiiO KA5 publishes at 32 Ω and at 300 Ω; HiBy FC4 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 only the FiiO KA5 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

4 headphones reach 100 dB on the FiiO KA5 but not on the HiBy FC4 — Moondrop COSMO, Symphonium Crimson, Symphonium Helios, 1 more.

561 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 Shure SE846: FiiO KA5 has +33 dB of headroom there against +29 dB. 4 dB is about 2.5 times the power, which matters for peaks rather than for how loud the music sits.

Hiss below about 20 dB SPL is inaudible in a quiet room.

Headphone	Impedance	Needs	FiiO KA5 headroom	HiBy FC4 headroom	FiiO KA5 hiss	HiBy FC4 hiss
Shure SE846	9 Ω	0.04 mW	+33 dB	+29 dB	19 dB	19 dB
Campfire Audio Andromeda 2020	9 Ω	4.0 mW	+13 dB	+9 dB	-1 dB	-1 dB
Audeze LCD-2 Classic	70 Ω	0.79 mW	+18 dB	+18 dB	-3 dB	-3 dB
Beyerdynamic DT 1990 Pro (250Ω)	250 Ω	0.63 mW	+14 dB	+13 dB	-8 dB	-7 dB
HiFiMAN HE400se	25 Ω	7.9 mW	+12 dB	+10 dB	-9 dB	-8 dB
Audio-Technica ATH-R70X	470 Ω	1.6 mW	+7 dB	+7 dB	-15 dB	-14 dB
Sennheiser HD 600	300 Ω	6.6 mW	+3 dB	+2 dB	-19 dB	-18 dB
HiFiMAN Susvara	60 Ω	50 mW	+1 dB	+1 dB	-21 dB	-20 dB

What the price difference buys

The gap in dollars, against the gap in numbers

These two cost the same, $99, so price settles nothing. Out of the 567 models here, the FiiO KA5 drives 4 models to 100 dB — and on the other side there is no such advantage at all.

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

Each in full: FiiO KA5 and HiBy FC4.