S.M.S.L builds gear for people who treat headphone listening as a serious pursuit. The H400 is a fully balanced, discrete component amplifier that delivers 15 watts per channel at 16 ohms and 7.5 watts at 32 ohms. That is enough power to drive nearly any planar magnetic headphone to its full potential without breaking a sweat.

The volume control uses electronic relays instead of a traditional potentiometer. This eliminates channel imbalance at low volumes, a common annoyance with analog knobs. You get three gain settings for both balanced and unbalanced inputs. On the balanced side, you can switch between -5.8dB, 6dB, and 20.4dB. The preamp output lets you use the H400 as a control center for powered speakers, adding flexibility beyond headphone duty. The internal power supply is efficient and runs quiet, even with demanding loads.

At 6.31 pounds, this is a heavy, solid chassis that stays planted on your desk. There is no Bluetooth or streaming built in, so you will need a separate DAC or source. That keeps the signal path clean and the design focused. If you want raw, clean power for hard-to-drive headphones and a preamp that doubles as a system hub, the H400 delivers without unnecessary extras.