Fosi Audio SK02 vs JDS Labs Atom+ (2nd gen)

Both are desktop amplifiers, $100 against $99. 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 JDS Labs Atom+ (2nd gen) reaches 100 dB on 566 of the 567 models here, the Fosi Audio SK02 on 564.

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. Fosi Audio SK02 publishes at 32 Ω; JDS Labs Atom+ (2nd gen) at 32 Ω, at 150 Ω and at 600 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 150 Ω and at 600 Ω only the JDS Labs Atom+ (2nd gen) 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.

2 headphones reach 100 dB on the JDS Labs Atom+ (2nd gen) but not on the Fosi Audio SK02 — Moondrop PARA, Symphonium Crimson.

26 headphones stay below the audible-hiss threshold on the JDS Labs Atom+ (2nd gen) but cross it on the Fosi Audio SK02 (64 Audio Fourte, AFUL Performer 8, Audio-Technica ATH-CKS1100, 23 more).

564 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 Audio-Technica ATH-R70X: JDS Labs Atom+ (2nd gen) has +20 dB of headroom there against +9 dB. 11 dB is about 13 times the power, which matters for peaks rather than for how loud the music sits.

Hiss is this source’s own noise, in decibels SPL, in that headphone — not a rating. Below about 20 dB SPL it is under the threshold of hearing in a quiet room; a negative figure means it is far below it.

The Fosi Audio SK02 costs $1 more than the JDS Labs Atom+ (2nd gen), and on these three axes the money buys nothing: among the 567 models here there is not one that the Fosi Audio SK02 handles and the JDS Labs Atom+ (2nd gen) does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper JDS Labs Atom+ (2nd gen) drives 2 models to 100 dB and keeps 26 below the audible-hiss threshold that the Fosi Audio SK02 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: Fosi Audio SK02 and JDS Labs Atom+ (2nd gen). Or put either against your own headphones in the source comparison tool.