Усилители мощности стерео — SMSL PA400

Foshan Shuangmusanlin Technology of China sells the PA400 under its SMSL brand, priced at USD 555. This two-channel class D amp is built with gallium nitride output devices and can be bridged to run as a single high-power mono channel, so two units can make a stereo pair.

Key specs that matter

In stereo the PA400 is rated at 250 W RMS per channel into 4 ohm. As a mono unit driven through XLR it reaches 500 W RMS into 8 ohm. SNR reaches 115 dB and channel separation 75 dB. Input sensitivity in stereo is 0.96 Vrms via RCA and 2.1 Vrms via XLR, and in mono through XLR it is 2.7 Vrms, all at 22 kohm input impedance. Consumption in normal use is 40 W, with standby below 0.5 W. The chassis measures 254 x 47.7 x 242 mm and weighs 2.58 kg.

Engineering and use context

Infineon GaN FETs switch at up to 1 MHz in the output stage. Level control is handled by a Texas Instruments PGA2311, a digitally controlled analogue volume chip that SMSL chose for fine steps and very low distortion. Inputs comprise a balanced XLR pair and a gold-plated RCA pair, plus a mono XLR mode, and speakers connect through high-current gold-plated binding posts. A stereo pass-through mode is intended for use with an external preamplifier, which then sets the level while the amplifier works as a pure power stage. In mono mode two units form a stereo system, and SMSL states that power rises about four times, so loudspeakers built to take high power are easily driven. The power supply has active power factor correction. Protection circuits cover overheating, overcurrent and other faults, and many audio-grade components are used in the signal path. The aluminium alloy chassis is CNC machined, which also helps carry heat away, and the finish is silver. SMSL publishes a firmware file for the model alongside the manual.

Pairing

A preamplifier or a volume-controlled DAC with XLR sockets suits the pass-through mode, while a fixed-level source can go straight into the RCA input and use the built-in volume chip. Listeners who want more headroom can buy a second PA400 and run the pair as bridged mono amplifiers. SMSL's own D200 DAC, which has XLR outputs and a remote-controlled volume stage, is one such source for the pass-through mode.

Alternatives

For a smaller GaN amplifier from SMSL, the PA200 delivers 160 W RMS per channel into 4 ohm in a 220 x 45.9 x 175 mm case.