SMSL PA400 Gallium Nitride Power Amplifier

The SMSL PA400 is a fully-balanced GaN power amplifier built around Infineon gallium nitride transistors. Capable of delivering up to 600 W with a distortion figure of just 0.003 %, it combines speed, control, and tonal evenness across the full frequency range. Designed for precision listening, it pairs naturally with reference DACs and preamps, driving both nearfield monitors and large passive speakers with equal confidence.

A new generation of GaN power

At the core of the PA400 is Infineon’s gallium nitride (GaN) power stage. Operating at a 1 MHz switching frequency—roughly double that of most Class D designs—it handles musical transients with incredible accuracy while keeping switching noise well outside the audible band. The result is fast, controlled bass, open midrange articulation, and treble that stays smooth even at high volume. With a THD+N of 0.003 % and a 115 dB signal-to-noise ratio, the amplifier reproduces silence as silence and preserves the micro-texture of recordings that would normally vanish into the noise floor.

Stereo balance or bridged power

The PA400 can operate as a balanced stereo amplifier or as a mono block in bridged configuration. In stereo mode, one chassis delivers linear, wide-band performance for critical listening environments. When run as a mono pair, total output power quadruples, giving ample current reserves for floor-standing speakers or large studio monitors. Switching between modes requires no internal modification—each configuration is clearly labeled on the rear panel for quick reference.

Precision machining and passive cooling

The chassis is CNC-carved from aerospace-grade aluminum alloy, with deep fins that function as both aesthetic detail and heat sink. This purely passive design keeps the amplifier quiet in every sense—no fans, no mechanical noise, no interference with nearby microphones or turntables. Even under sustained high output, the PA400 maintains stable thermal performance without throttling or distortion.

Engineered reliability

A dedicated 600 W switching power supply provides continuous current to the output stage, while built-in protection circuitry guards against overheating and overcurrent events. The control knob is milled from solid aluminum and turns with steady, damped resistance. Rubber-damped feet reduce vibration transfer to the surface below. Each of these design choices contributes to mechanical stability and long-term dependability.

Seamless system integration

Balanced XLR and single-ended RCA inputs accommodate both modern DACs and legacy line sources. Gold-plated binding posts minimize contact resistance and support a wide range of speaker cables. Whether integrated into a desktop reference chain or a full-size listening room system, the PA400’s electrical neutrality allows the upstream components to define the system’s character.

Who it’s for

The PA400 suits listeners who value measured transparency over coloration. System builders seeking Class D efficiency without the usual sterility will appreciate its GaN topology and low noise floor. It’s equally at home in a professional mix room, a two-channel hi-fi rig, or any system where silent operation and high output power are essential. 

Availability

The SMSL PA400 Gallium Nitride Power Amplifier is available now on Apos Audio.