Stax SRM-400S

• Transistor output stage without negative feedback
  
• Symmetrically designed circuit
  
• Volume/balance control via quadruple potentiometer
  
• One switchable input: either balanced (XLR) or unbalanced (RCA/Cinch)
  
• One unbalanced output (RCA/Cinch)
  
• Two headphone outputs (simultaneous operation of two STAX headphones possible)
  

With the SRM-400S transistor driver amplifier, STAX offers a further development of the proven SRM-353X mid-range model as an ideal power supply for the electrostatic headphones from the traditional Japanese manufacturer, such as those in the Lambda series (STAX SR-L300, STAX SR-L500 MK2, STAX SR-L700 MK2) or for upgrading the entry-level model SRS-3100.

What's new?
The SRM-400S features a newly developed DC amplifier stage, modeled on the sophisticated circuit design of the SRM-700S top-of-the-line amplifier. With specially manufactured and extremely low-noise DUAL-FET transistors, the amplifier's outstanding sound quality is once again raised to a new level. For improved efficiency with simultaneously lower power consumption, the SRM-400S is also equipped with a new transformer with separate windings for the high and low voltage circuits. The better stiffened and resonance-free steel housing with an increased proportion of non-magnetic aluminum effectively reduces both vibrations and eddy currents, providing the SRM-400S with an even more undisturbed working environment.

By improving components and modifying the circuit layout, the new transistor driver amplifier sets entirely new sonic standards in this price range.

Connectivity
Driver amplifiers for STAX electrostatic headphones can be operated from the recording output (Tape/Record Out or Fixed Out) or from another output with a fixed level (Pre Out/Fixed Out) of a preamplifier or integrated amplifier. Of course, a CD player or a turntable with a separate phono preamplifier can also serve directly as the signal source. The music signal present at the input of the driver amplifier can be looped through – thus, another device can be supplied with music signals. A separate D/A converter is required for digital connection of a source device.

Note on the operating voltage (polarization voltage) of STAX headphones
Many early STAX headphones are designed for an operating voltage of 230V/DC. Headphones of the PRO series – including all current models – require a higher operating voltage of 580V/DC.
In the past, driver amplifiers were offered which also provided both operating voltages. Current devices only have connections for the higher operating voltage of 580V/DC.
To avoid confusion, the connection jacks for the different operating voltages have different contact configurations.