FiiO KA15 vs Hidizs S9 Pro Plus

Both are dongles, $109 against $139. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?

The FiiO KA15 reaches 100 dB on 566 of the 567 models here, the Hidizs S9 Pro Plus on 562.

A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.

Both makers publish a power rating, which is less common than the table above makes it look: of the 280 sources here, 209 publish a figure at at least one load and only 2 publish one at all four. FiiO KA15 publishes at 32 Ω and at 300 Ω; Hidizs S9 Pro Plus at 32 Ω. Every other row is worked out from those — between two published loads, or beyond them holding voltage constant, which understates rather than flatters.

So the two columns are not equally firm row by row: at 300 Ω only the FiiO KA15 figure is the maker’s own. On those rows the derived number is the one to doubt first.

What each of these labels means, and why a derived figure is still worth printing, is set out in how this data was built.

4 headphones reach 100 dB on the FiiO KA15 but not on the Hidizs S9 Pro Plus — Moondrop COSMO, Moondrop PARA, Symphonium Crimson, 1 more.

562 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.

The counts above say how many models the two treat differently. This says by how much. The same 8 headphones appear on every page of this kind, ordered from the easiest to drive to the hardest, so a row can be read across pages as well as across columns. Headroom is at a 100 dB SPL peak.

The widest gap on the list is the Shure SE846: FiiO KA15 has +36 dB of headroom there against +30 dB. 6 dB is about 4.2 times the power, which matters for peaks rather than for how loud the music sits.

The hiss columns are empty for Hidizs S9 Pro Plus because that maker publishes no output noise figure. That is a gap in the specification, not a quiet amplifier, and it is left blank here rather than filled with a plausible number.

The Hidizs S9 Pro Plus costs $30 more than the FiiO KA15, and on these three axes the money buys nothing: among the 567 models here there is not one that the Hidizs S9 Pro Plus handles and the FiiO KA15 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper FiiO KA15 drives 4 models to 100 dB that the Hidizs S9 Pro Plus does not.

Everything in this paragraph counts only figures the two makers published. An advantage on an axis one of them leaves blank cannot be counted, and is not counted — how often that happens is its own page.

Each has a page of its own with every power figure traced to what the maker published and a full headphone list: FiiO KA15 and Hidizs S9 Pro Plus. Or put either against your own headphones in the source comparison tool.