18W Gallium Nitride Balanced Amp

The SMSL H400 MK2 is a compact desktop headphone amplifier and preamp built around a fully-balanced discrete architecture, 14 OPA1612A operational amplifiers, three selectable gain levels, and a custom low-noise gallium nitride power supply. Balanced and unbalanced inputs and outputs give it the flexibility to serve sensitive IEMs, full-size headphones, and a dedicated desktop audio system.

Fully-balanced amplification

The H400 MK2 uses a fully-balanced discrete component architecture with symmetrical signal paths designed to reduce interference throughout the amplification stage. Its balanced headphone output reaches up to 18W per channel into 16Ω, giving the amplifier substantial power for demanding headphones while selectable gain settings provide finer control with more sensitive models.

Parallel op-amp architecture

Fourteen OPA1612A audio operational amplifiers work in a parallel noise-reduction architecture. The design supports a measured SNR of up to 132dB and THD+N as low as 0.00006% at 1kHz and 32Ω, helping maintain low noise and distortion across the signal path.

Three gain levels

Low, middle, and high gain settings let you match the amplifier to a broad range of headphones. Balanced gain ranges from -5.5dB to 19.6dB, while unbalanced gain ranges from -11.5dB to 13.6dB. Low gain is suited to sensitive IEMs, while the middle and high settings provide additional voltage gain for full-size headphones with impedances up to 600Ω.

Gallium nitride power supply

A custom low-noise gallium nitride power supply provides efficient power conversion with reduced switching noise. Its fast transient response is designed to supply current quickly during demanding passages while generating less heat during extended operation.

Balanced and unbalanced connections

The front panel provides a 4.4mm balanced headphone output, a balanced XLR headphone connection, and a 6.35mm unbalanced headphone output. Rear-panel connectivity includes XLR balanced inputs, RCA inputs, XLR pre-outputs, and RCA pre-outputs, allowing the H400 MK2 to work as both a headphone amplifier and a volume-controlled preamp.

Relay-controlled volume

Volume is controlled by relay, supporting precise level adjustment for headphone and preamp use. The front control knob is paired with a clear IPS color display that keeps volume and operating information visible at a glance.

Compact aluminum chassis

The CNC-machined aluminum alloy enclosure measures approximately 10.0 x 1.89 x 7.44 inches (254 x 48 x 189 mm), keeping the H400 MK2 compact enough for a desktop system. The metal chassis also provides structural rigidity, heat dissipation, and electromagnetic shielding for the internal circuitry. Black and silver finishes are available.

Protection circuitry

Integrated DC, over-voltage, and overload protection monitors the amplifier during operation. These protection systems are designed to respond to abnormal electrical conditions and help protect both the connected headphones and the amplifier.

Product highlights

• Fully-balanced discrete headphone amplifier architecture
  
• 14 OPA1612A operational amplifiers
  
• Custom low-noise gallium nitride power supply
  
• Three selectable gain levels
  
• Up to 18W x 2 balanced output power into 16Ω
  
• SNR up to 132dB
  
• THD+N as low as 0.00006% at 1kHz and 32Ω
  
• 4.4mm, XLR balanced, and 6.35mm headphone outputs
  
• XLR and RCA analog inputs
  
• Balanced XLR and unbalanced RCA pre-outputs
  
• Relay-controlled volume
  
• Full-lamination IPS color display
  
• CNC-machined aluminum alloy chassis
  
• DC, over-voltage, and overload protection

Specs

• Inputs: XLR balanced, RCA unbalanced
  
• Headphone outputs: 4.4mm balanced, XLR balanced, 6.35mm unbalanced
  
• Pre-outputs: XLR balanced, RCA unbalanced
  
• Balanced output power at 16Ω: 18W x 2
  
• Balanced output power at 32Ω: 9W x 2
  
• Balanced output power at 300Ω: 1100mW x 2
  
• Balanced output power at 600Ω: 550mW x 2
  
• Unbalanced output power at 16Ω: 5W x 2
  
• Unbalanced output power at 32Ω: 2.5W x 2
  
• Unbalanced output power at 300Ω: 260mW x 2
  
• Unbalanced output power at 600Ω: 130mW x 2
  
• SNR: 132dB
  
• Dynamic range: 132dB
  
• THD+N: -123dB, 0.00006% at 1kHz and 32Ω
  
• Input impedance: 47kΩ
  
• Amplifier output impedance: Near 0Ω
  
• Balanced pre-output impedance: 44Ω
  
• Unbalanced pre-output impedance: 22Ω
  
• Frequency response: 20Hz to 100kHz, -0.5dB
  
• Balanced gain: Low -5.5dB, middle 6dB, high 19.6dB
  
• Unbalanced gain: Low -11.5dB, middle 0dB, high 13.6dB
  
• Power consumption: Less than 100W
  
• AC input: 100V to 240VAC
  
• Dimensions: 10.0 x 1.89 x 7.44 inches (254 x 48 x 189 mm), W x H x D
  
• Weight: 4.85 lb (2.2 kg)

What’s included

• SMSL H400 MK2 headphone amplifier