Stax SRM-400S Earspeaker Driver Unit


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Driver unit for electrostatic earspeakers

The Stax SRM-400S Earspeaker Driver Unit is a mid-range, solid-state amplifier designed to power Stax's high-end, electrostatic headphones. It boasts several exciting improvements over previous models and delivers exceptional sound quality for audiophiles seeking to elevate their listening experience with Stax's electrostatic headphones.

Enhanced sound quality

The SRM-400S utilizes a newly designed power transformer and all-stage FET amplification, resulting in lower distortion and a wider frequency response. This translates to a more accurate and detailed listening experience.

Improved build quality

The unit features a sturdier aluminum chassis that minimizes vibrations and external noise interference, contributing to a cleaner audio output.


It offers both RCA and XLR inputs, making it compatible with a variety of audio sources.


  • Type: 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: 50kΩ (RCA), 50kΩx 2 (XLR)
  • Maximum output voltage: 400Vrms (1kHz)
  • Bias voltage: DC 580V
  • Operating temperature / humidity: 0 to 35 degrees C / 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

Due to the bespoke nature of our high-end music systems this product is not available to be purchased online. Please contact us for personalized service from one of our team of experts.