Stax SRM-400S Semiconductor Electrostatic Driver: Precision Control with Modern FET Authority Presence The SRM-400S steps into the Stax lineage with a confident, modern presence, bringing semiconductor precision into a compact, purpose-built chassis. It anchors a high-resolution electrostatic system with authority, offering a clean, controlled foundation that supports the full expressive range of Stax earspeakers. Design Stax engineers this driver unit around a fully DC-coupled, all-stage FET configuration that eliminates coupling capacitors from the signal path. This approach preserves signal purity and keeps transient information intact. You hear a direct, unfiltered presentation that prioritises speed, clarity, and tonal accuracy. Circuitry Carefully selected dual low-noise FETs operate across the amplification stages, maintaining channel consistency and reducing distortion. The design borrows principles from higher-tier Stax units, refining stability and linearity to achieve a balanced and highly resolved sound signature. Power A dedicated transformer system improves efficiency and supports stable high-voltage delivery. The SRM-400S generates the bias and drive voltage required for electrostatic transducers with confidence, ensuring consistent control across dynamic peaks and quiet passages alike. Performance You experience a sound that combines precision with natural flow. Bass remains tight and structured, midrange reveals fine texture, and treble extends with openness and air. The amplifier maintains composure under load, delivering clarity without hardness and detail without fatigue. Control A smooth dual-concentric volume system allows precise level adjustment, keeping channel balance stable at all listening levels. You gain fine control over playback without disrupting signal integrity, allowing sessions that remain focused and immersive. Integration Balanced XLR and single-ended RCA inputs provide flexible system matching. You connect it easily into high-quality preamplifier chains, while RCA loop outputs support system expansion. The SRM-400S adapts cleanly into both entry and advanced electrostatic setups. Build A reinforced aluminium chassis reduces vibration and external interference. The compact form factor fits neatly into dedicated headphone systems while maintaining a robust, engineering-led feel that reflects its performance-first design philosophy. The SRM-400S delivers precise electrostatic control with refined FET architecture, offering speed, transparency, and composure for serious headphone listening systems. Feature Specification Type All-stage FET DC-coupled electrostatic headphone driver Circuit Topology Fully DC amplifier (no coupling capacitors) Frequency Response DC – 90 kHz Gain 60 dB Harmonic Distortion ≤ 0.01% (1 kHz / 100 Vrms) Maximum Output Voltage 400 Vrms (1 kHz) Bias Voltage DC 580 V Input Impedance 50 kΩ (RCA), 50 kΩ × 2 (XLR) Inputs 1 × RCA, 1 × XLR (mutually exclusive) Outputs RCA parallel output Power Consumption 30 W Dimensions (W × H × D) 195 × 102 × 376 mm Weight 3.4 kg Operating Conditions 0–35°C, <90% humidity (non-condensing)
