SMSL SP400 THX AAA 888 Headphone Amp


Dang it.

This product has been discontinued. Luckily, we have a great alternative in the SMSL SH-9 THX AAA-888 Balanced Headphone Amp.

An SMSL classic gets a makeover  

The SMSL SP400 arrives just over a year after the release of its predecessor, the SP200. The SP200 wowed reviewers with its “vanishingly low distortion and tons of power.” The SP400 retains the THX AAA-888 amplifier of its predecessor and, with it, most of its predecessor’s specs. So how’s it different?

You’ll find most of the upgrades on the box itself. The SP400 has been given a nice bright 1.9” LCD display, a full-function remote, and a pre-balanced output. Plus, it matches the SM400 DAC in size and style, so you’ll be able to stack the two with ease. 

Power for all your headphones

Is it powerful enough to drive all your headphones? The answer in this case is (almost) definitely. With 12W at 16Ω and 6W at 32Ω, the SP400 can power nearly everything. And if you need a little extra oomph, just toggle the three-position gain for an extra three to six decibels.

(If you’re unsure about your headphone’s power requirements, check out this handy headphone power calculator, courtesy of DigiZoid.)

The THX AAA-888 offers extreme clarity

The THX AAA lineup of amps are known for their power and clarity. Unlike many amplifiers, THX AAA amps use a feed-forward error correction topology that removes common distortion issues. To put it simply, the amp measures errors in an early part of the system and corrects them in a later part of the system. 

Pure black background

The THX AAA-888 is the most sophisticated iteration of the lineup. Its distortion levels are seriously low. Signal-to-noise ratio is 133dB, meaning that you’d have to crank the amp up to 134dB before hearing any hiss. And unless you’re trying to permanently damage your eardrums, you’re probably not going to do that. 

Desktop friendly

Despite its massive output capabilities, the SP400 is actually quite small. At 8.6” on its longest size, you should have no problem fitting it onto most desktops. And as we said, it’s designed to stack with the M400. Together, the pair reach just over three inches in height.

Product highlights

  • THXAAA-888 Headphone Amplifier with THX AAA Technology
  • Ultra-compact design
  • Balanced stereo headphone output
  • Pre-amplifier application
  • Balanced stereo line input
  • High precision resistors for temperature stability
  • Pop-less design with high-quality relays
  • High precision and low noise 256-level relay volume control
  • 3-position switchable gain control
  • DC, over-voltage, over-current, short-circuit and thermal protection
  • High-efficiency ultra-low-noise power supply
  • Full function remote
  • 1.9” LCD display


  • Inputs: 1 balanced, 1 unbalanced
  • Outputs: 1 balanced, 1 unbalanced, 1 pre-balanced
  • Output power
    • Balanced
      • 12W x 2 (16Ω)
      • 6W x 2 (32Ω)
      • 880mW x 2 (300Ω)
      • 440mW x 2 (600Ω)
    • Unbalanced
      • 6W x 2 (16Ω)
      • 3W x 2 (32Ω)
      • 440mW x 2 (300Ω)
      • 220mW x 2 (600Ω)
  • SNR: 133dB, A-weighted
  • Output noise: 1.9uV, A-weighted
  • THD+N: -123dB, 0.00007% (1kHz, 32Ω)
  • THD+N: -117dB, 0.00013% (20-20kHz, 32Ω, -3dB)
  • THD: <-125dB, 0.00006%
  • Input impedance: 47kΩ
  • Output impedance: Near 0 Ω
  • Frequency Response: 0.1Hz - 500,000Hz(-3dB)
  • Power supply voltage/frequency: AC100-240V, 50-60Hz
  • Power consumption (EN60065): <40W
  • Power consumption in standby mode: <0.1W
  • Size: 8.66 x 8.4 x 1.69” (220 x 215 x 43mm)
  • Weight: 2.9lbs (1330g)

What’s included

  • SMSL SP400
  • User Manual
  • Remote control
  • Power supply cord

What pairs well

Featured reviews

"Amazing value." -SoundNews

"The best THX amplifier I've ever heard." -Z Reviews

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SMSL SP400 THX AAA 888 Headphone Amp User Manual Download

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