Stax SRM-270S
Stax amplifier dedicated to electrostatic headphones, designed in Japan with an extruded aluminium housing for improved heat dissipation.
Description
The Stax SRM-270S is an amplifier dedicated to electrostatic headphones, designed to deliver the bias voltage required for this type of transducer to operate. It is not a conventional headphone amplifier: its output stage supplies a much higher voltage than a standard dynamic amplifier, essential for driving a Stax electrostatic headphone.
The amplifier's first stage relies on a recent low-noise FET, while the output stage uses an improved emitter-follower circuit. The bias voltage reaches 580 V DC, and the maximum output voltage rises to 280 V rms at 1 kHz, with an amplification of 58 dB, equivalent to a factor of 800 times the input signal. Harmonic distortion remains contained at 0.01% or less at 1 kHz for a 100 V rms output, and the frequency response extends from DC up to 35,000 Hz.
The extruded aluminium housing, paired with a 3 mm thick aluminium front panel, has been enlarged compared with the previous model to improve heat dissipation. The unit features a single RCA input and a parallel output, allowing it to be easily inserted into an existing system without monopolising the only available input on the source.
This model is aimed at owners of Stax electrostatic headphones looking for a compact amplifier capable of powering them correctly, whether in a desktop setup or a small system dedicated to headphone listening. Its parallel output makes it easy to integrate into an existing system without requiring any cabling reconfiguration.
Technical specifications
| Frequency response | DC up to 35,000 Hz/+0, -3 dB |
| Harmonic distortion | 0.01% or less/1 kHz 100 V rms |
| Amplification | 58 dB (800x) |
| Nominal input level | output 125 mV/100 V rms |
| Maximum output voltage | 280 V rms/1 kHz |
| Input impedance | 25 kΩ |
| Input terminal | RCA x 1 |
| Output terminal | parallel output x 1 |
| Bias voltage | DC580V |
| Power supply voltage | mains adaptor included |
| Power consumption | DC12 V/500 mA |
| Dimensions (H × W × D) | 38 x 132 x 153 mm (excluding protrusions) |
| Weight | 540 g |
| Country of origin | Japan |
What to check before buying used
Check that the bias voltage does indeed reach 580 V (if not, this indicates a faulty power supply or output stage) and test the unit with a compatible Stax electrostatic headphone, listening across the full level range to detect any crackling or distortion revealing ageing capacitors. Also check the condition of the RCA socket and the parallel output connector, as well as the supplied DC 12 V/500 mA mains adaptor, whose cable or plug may wear over time.
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