STAX SRM-400S

The STAX SRM-400S is STAX's mid-tier all-stage FET electrostatic driver, the successor to the SRM-353X, bringing the fully FET-configured DC amplifier architecture of the flagship SRM-700S to a more accessible price point with improved power efficiency and a more rigid, vibration-resistant chassis.

Type and Technology

All-stage FET DC amplification electrostatic driver. STAX custom-made low-noise dual FET in the first stage, with FET also installed in the last stage, all stages fully FET-configured, matching the design philosophy of the SRM-700S. Complete DC amplifier configuration with no coupling condensers in the signal circuit. New power transformer with low-voltage winding for improved power efficiency and sound quality versus the SRM-353X. New rigid hybrid aluminum chassis for reduced environmental noise and vibration. RCA and XLR inputs (mutual exclusion). RCA parallel output. 400V RMS maximum output. High-quality film capacitors. 3.4kg.

Sound Character

Clean, highly resolving, and dynamically alive in the STAX FET tradition, the all-FET configuration prioritizes low noise and high resolution over the tonal warmth of tube-based drivers. The SRM-400S delivers excellent bass definition and low-level detail retrieval, and is an appropriate match for the full Lambda series from the SRS-3100 to the SR-L700 MK2.

Build and Finish

Compact at 195 x 102 x 376mm. Non-magnetic aluminum chassis construction for minimal environmental noise interference. All components selected for environmental compliance and sound quality.

Best For

Listeners upgrading from the SRS-3100 entry system or pairing with Lambda series earspeakers who want solid-state FET driver performance at an accessible mid-range price.

Specifications