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The SMSL H400 MK2 is a fully balanced desktop headphone amplifier, designed to drive both sensitive IEMs and planar magnetic as well as high-impedance dynamic headphones. Its four-channel PLFC+ circuit delivers up to 18W per channel into 16Ω, relying on fourteen OPA1612A operational amplifiers to maintain a stable and detailed rendering across a wide range of headphones.
Intended for stationary setups requiring a high power reserve, it combines balanced and unbalanced headphone outputs, three-level gain adjustment, and XLR and RCA preamplified outputs. This versatility allows it to drive a headphone or to serve as a preamplifier for active speakers, while maintaining a low noise level thanks to its GaN power supply and its fully balanced analog architecture.
The SMSL H400 MK2 is a fully balanced desktop headphone amplifier, designed to drive planar magnetic or high-impedance dynamic headphones. Its patented four-channel PLFC+ circuit delivers up to 18W per channel into 16Ω and 9W into 32Ω, while the fourteen OPA1612A operational amplifiers work in parallel to sustain transients and dynamic swings without limiting the most demanding headphones.


This analog architecture achieves a THD+N distortion of only 0.00006%, combined with a signal-to-noise ratio and dynamic range of 132dB. The H400 MK2 thus maintains a very low noise floor, which preserves micro-information, ambiences, and variations in intensity, including during low-level listening.
The custom gallium nitride (GaN) power supply provides a high current reserve while limiting switching noise. Its transient response follows the rapid variations in power demand, while the contained thermal dissipation promotes consistent stability during long listening sessions.


Volume adjustment relies on a high-precision relay-based electronic controller. This stepped control limits imbalances between the left and right channels, even at very low levels, in order to maintain a centered stereo image when using sensitive earphones.
The H400 MK2 offers three gain levels suited to different types of headphones. The Low mode goes down to -5.5dB in balanced and -11.5dB in unbalanced, which reduces the risk of hiss with sensitive IEMs, while the higher levels make use of the available power reserve with planar magnetic headphones and high-impedance models.


The headphone connectivity includes a 4.4mm output, a 4-pin XLR output, and a 6.35mm Jack output, allowing the amplifier to be adapted to most stationary configurations. Beyond this function, the balanced XLR and RCA preamplified outputs allow its integration with active speakers, while the Floating/Grounded ground selector helps limit ground loops in more complex systems.
The whole is housed in an ultra-compact CNC-machined aluminum chassis, whose rigidity and electromagnetic shielding help protect the environment of the audio circuits. This design is complemented by a fully laminated IPS color screen protected by a tempered glass panel, which improves legibility while reducing reflections from various listening positions.


| 1 | 4.4mm Jack headphone output |
| 2 | 6.35MM Jack headphone output |
| 3 | 4-pin XLR headphone output |
| 4 | Volume knob |
| 5 | IR receiver |
| 6 | Indicator light |
| 7 | Screen |
| 8 | XLR input |
| 9 | XLR output |
| 10 | Grounding |
| 11 | RCA input |
| 12 | RCA output |
| 13 | USB-C update port |
| 14 | Grounding switch |
| 15 | Power input |
Technical characteristics
| Specifications | |
|---|---|
| Product type | Headphone amplifier Preamplifier |
| Inputs | 1x stereo XLR 1x stereo RCA |
| Outputs | 1x stereo XLR 1x stereo RCA 1x 4.4mm Jack headphone output 1x 6.35MM Jack headphone output 1x 4-pin XLR headphone output |
| Output power | Balanced: 2x18W @16Ω Balanced: 2x9W @32Ω Balanced: 2x1100mW @300Ω Balanced: 2x550mW @600Ω |
| Signal-to-noise ratio (SNR) | 132dB |
| Dynamic range | 132dB |
| Total harmonic distortion more noise (THD+N) | -123dB, 0.00006% @1khz, 32Ω |
| Input impedance | 47kΩ |
| Output impedance | Headphone output: →0Ω Balanced pre-out: 44Ω Unbalanced pre-out: 22Ω |
| Frequency response | 20Hz-20kHz (-0.5dB) |
| Gain | Balanced, low gain: -5.5dB Balanced, medium gain: 6dB Balanced, high gain: -19.6dB Unbalanced, low gain: -11.5dB Unbalanced, medium gain: 0dB Unbalanced, high gain: -13.6dB |
| General | |
|---|---|
| Supply voltage | 100-240V AC |
| Consumption | <100W |
| Dimensions | 189 x 254 x 48mm |
| Weight | 2.2kg |
| Package | 1x SMSL H400 MK2 1x Power cable |
| Input | XLR |
| Input | RCA |
| Output | XLR |
| Output | Jack 4.4mm |
| Output | RCA |
| Output | Jack 6.35mm |
| Color | Black |
| Class | Class D / T |
| Remote Control | Yes |