Усилители для наушников — Stax SRM-D10 II

The SRM-D10 II is a portable driver unit for electrostatic earspeakers from STAX, the Japanese company that specialises in electrostatic headphones. Announced in January 2024 in connection with the company's 85th anniversary, it replaces the original SRM-D10 in the STAX portable range at an MSRP of USD 945. Besides amplifying analogue signals, it contains a DAC, so it can take a digital signal directly from a phone or computer.

Key specs that matter

STAX fits an AKM AK4493 converter, an upgrade over the predecessor, handling PCM up to 32 bit and 384 kHz and DSD up to DSD256. Inputs are USB-C for digital audio and a 3.5 mm analogue input, and the unit charges over USB-C. Gain is 53 dB, or 450 times, and THD is 0.025% or less from 1 kHz to 10 kHz. Maximum output is 200 V RMS from 100 Hz to 10 kHz, and the bias voltage is 580 V DC. The line input has an impedance of 10 kOhm, a rated input of 230 mV for 100 V output and a maximum input of 10 V. The built-in battery lasts about 4.5 hours on the analogue input and about 3.5 hours on the digital input. The unit accepts DC supplies of 5, 9, 12 or 15 V. The aluminium alloy case measures 75 x 32 x 141 mm and weighs 450 g.

Engineering and use context

Electrostatic earspeakers work differently from dynamic headphones. A very thin diaphragm carries a fixed high-voltage charge and sits between two perforated electrodes, and the audio signal, applied as a high voltage to the electrodes, moves the diaphragm. A driver unit therefore has to supply a constant bias voltage for STAX PRO-bias earspeakers and amplify the music signal to hundreds of volts. A normal headphone amplifier cannot do this, which is why STAX earspeakers always need an energiser like the SRM-D10 II. Fitting this circuit into a small battery-powered unit makes electrostatic listening possible away from the mains. The AK4493 DAC takes the digital signal over USB-C from a phone, tablet or computer, so no separate converter is required. The high gain lets the unit reach full output from a modest line signal on the analogue input. Battery life is shorter on the digital input because the DAC draws additional power.

Pairing

The SRM-D10 II drives all STAX earspeakers that use the PRO bias, and it was earlier sold as a set with the SR-003MKII in-ear earspeaker in its first version. A phone or computer connects through USB-C, and a portable player through the analogue input.

Alternatives

The STAX SRM-D10 is the original portable driver unit that this model replaces, using an earlier DAC.