NEW: SMSL H400 MK2 Headphone Amplifier
18W balanced output and a GaN power supply
The SMSL H400 MK2 is a compact desktop headphone amplifier and preamp built around a fully balanced discrete amplification architecture, 14 OPA1612A operational amplifiers, three selectable gain levels, and a custom low-noise gallium nitride power supply. Its balanced headphone output delivers up to 18W per channel into 16Ω, while measured performance reaches a 132dB signal-to-noise ratio and THD+N as low as 0.00006% at 1kHz into 32Ω. With balanced and unbalanced analog inputs, three headphone output formats, and dedicated preamp outputs, the H400 MK2 is designed to cover sensitive IEMs, full-size headphones, and desktop systems using powered speakers or a separate power amplifier.
Fully balanced discrete amplification
The H400 MK2 uses a fully balanced discrete architecture with symmetrical signal paths through the amplification stage. Maintaining separate positive and negative signal paths helps reject common-mode interference while keeping the balanced channel topology consistent from input through output.
Its balanced headphone output reaches 18W per channel into 16Ω, providing substantial current capability for low-impedance headphones. Selectable gain allows that output stage to be used across a wider range of loads without forcing sensitive headphones or IEMs into an unnecessarily high-gain operating range.
Parallel OPA1612A architecture
Fourteen OPA1612A audio operational amplifiers are used in a parallel noise-reduction architecture. Distributing the signal-stage workload across multiple devices helps lower aggregate noise while supporting the current demands of the amplifier circuit.
The resulting measured signal-to-noise ratio reaches up to 132dB, reducing residual circuit noise when the amplifier is paired with high-sensitivity downstream equipment. THD+N is specified as low as 0.00006% at 1kHz into 32Ω, keeping harmonic and noise components at a low level under that measured operating condition.
Three selectable gain levels
Low, middle, and high gain settings allow the H400 MK2 to accommodate headphones with substantially different sensitivity and impedance requirements. Balanced gain ranges from -5.5dB to 19.6dB, while unbalanced gain ranges from -11.5dB to 13.6dB.
The lower settings provide more usable volume-control range with sensitive IEMs and efficient headphones, while middle and high gain add voltage gain for less sensitive full-size models, including headphones with impedances up to 600Ω.
Gallium nitride power supply
A custom low-noise gallium nitride power supply handles power conversion inside the H400 MK2. GaN switching devices can operate at high switching speeds, which allows the supply to respond quickly to changing current demand while SMSL's implementation is designed to keep switching noise from coupling into the audio circuitry.
The supply is also intended to reduce heat generation during extended operation, an important consideration in a compact chassis housing a high-output balanced amplifier.
Balanced and unbalanced connectivity
The front panel provides 4.4mm balanced, XLR balanced, and 6.35mm single-ended headphone outputs, allowing the amplifier to connect directly to most common desktop headphone terminations without adapters.
Rear-panel connections include XLR balanced and RCA unbalanced analog inputs, along with XLR and RCA preamp outputs. The H400 MK2 can therefore operate as a dedicated headphone amplifier or as a volume-controlled analog preamp feeding powered monitors or an external power amplifier.
Relay-controlled volume
Volume adjustment is relay controlled, giving the H400 MK2 a discrete switching mechanism for level control rather than relying solely on a conventional analog potentiometer. This approach is intended to maintain precise level adjustment for both headphone and preamp operation.
A front-mounted control knob handles volume and system operation, while a full-lamination IPS color display presents volume level and operating information.
CNC-machined aluminum chassis
The enclosure is CNC machined from aluminum alloy and measures approximately 10.0 x 1.89 x 7.44 inches (254 x 48 x 189 mm). The relatively low-profile chassis keeps the amplifier suitable for desktop use while providing a rigid enclosure around the internal circuitry.
The metal construction also contributes to heat dissipation and electromagnetic shielding. The H400 MK2 is available in black and silver finishes.
Protection circuitry
Integrated DC, over-voltage, and overload protection monitor the amplifier for abnormal electrical conditions during operation. These circuits are designed to intervene when operating limits are exceeded, helping protect both the amplifier and connected headphones from potentially damaging fault conditions.
