Both are desktop amplifiers, $176 against $169. 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 xDuoo MT-604 reaches 100 dB on 567 of the 567 models here, the Little Dot MK II on 560.
| Specification | Little Dot MK II | xDuoo MT-604 |
|---|---|---|
| Power into 32Ω | 100 mW | 2.0 W |
| Power into 150Ω | 214 mW | 427 mW |
| Power into 300Ω | 300 mW | 213 mW |
| Power into 600Ω | 150 mW | 107 mW |
| Output impedance | not published | not published |
| Output noise | not published | not published |
| Price | $176 | $169 |
| Headphones it reaches 100 dB on out of 567 | 560 | 567 |
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.
| Load | Little Dot MK II | xDuoo MT-604 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
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. Little Dot MK II publishes at 32 Ω and at 300 Ω; xDuoo MT-604 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 Little Dot MK II 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.
7 headphones reach 100 dB on the xDuoo MT-604 but not on the Little Dot MK II — Moondrop COSMO, Moondrop PARA, Moondrop PARA 2, 4 more.
560 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 HiFiMAN HE400se: xDuoo MT-604 has +23 dB of headroom there against +10 dB. 13 dB is about 20 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Little Dot MK II and xDuoo MT-604 because neither 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.
| Headphone | Impedance | Needs | Little Dot MK II headroom | xDuoo MT-604 headroom | Little Dot MK II hiss | xDuoo MT-604 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +28 dB | +42 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +8 dB | +22 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +22 dB | +31 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +26 dB | +26 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +10 dB | +23 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +21 dB | +19 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +17 dB | +15 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +4 dB | +13 dB | not published | not published |
The Little Dot MK II costs $7 more than the xDuoo MT-604, and on these three axes the money buys nothing: among the 567 models here there is not one that the Little Dot MK II handles and the xDuoo MT-604 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper xDuoo MT-604 drives 7 models to 100 dB that the Little Dot MK II 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: Little Dot MK II and xDuoo MT-604. Or put either against your own headphones in the source comparison tool.