Stax SRM-400S Semiconductor Driver Unit

The Stax SRM-400S represents a significant evolution in electrostatic amplification, building upon the engineering excellence of the flagship SRM-700S. This semiconductor driver unit features precision-matched dual FETs in both the first and final stages, delivering the low-noise performance essential for high-resolution audio reproduction. The redesigned power transformer incorporates dedicated low-voltage windings that enhance efficiency and acoustic clarity beyond previous models like the SRM-353X. A rigid hybrid chassis constructed from non-magnetic aluminum effectively isolates the circuitry from environmental vibrations and interference. The complete DC amplifier topology—eliminating coupling capacitors from the signal path—preserves the transparency and dynamic range characteristic of semiconductor designs. Dual RCA and XLR inputs with parallel output connectivity provide flexible integration into professional and audiophile systems. Meticulously selected components throughout ensure consistent performance and tonal balance across the frequency spectrum. Whether upgrading from entry-level equipment or pairing with advanced Lambda series headphones, the SRM-400S delivers refined sound quality suitable for both discerning beginners and experienced listeners.

All-stage FET configuration DC amplification driver unit
Frequency response: DC - 90kHz (with one SR-L500 MK2)
Gain: 60dB
Harmonic distortion: 0.01% or less (1kHz/100Vrms output)
Input impedance: 50k Ω (RCA), 50k Ω x 2 (XLR)
Maximum output voltage: 400Vrms (1kHz)
Bias voltage: DC 580V
Operating temperature / humidity: 0 to 35 degrees celsius / less than 90% (non condensing)
Input terminal: RCA x 1, XLR x 1(mutual exclusion input)
Output: RCA parallel output terminal
Power consumption: 30W
Dimension: 195 (W) x 102 (H) x 376 (D) mm (maximum protruding portion included)
Weight: 3.4kg