Усилители для наушников — Stax SRM-D50

The SRM-D50 is a mains-powered driver unit for electrostatic earspeakers and also houses a DAC, built by Stax of Japan. According to the company it takes its inspiration from the battery-powered SRM-D10, and it was introduced in 2018 so that one box could accept computer, disc and analogue sources. A US list price of USD 1,260 is quoted for it.

Key specs that matter

Inside is an ESS DAC chip accepting PCM up to 32 bit and 384 kHz, plus DSD files at up to 5.6 MHz. For digital sources there are three sockets - USB Type B, optical TOSLINK and coaxial - and a single RCA pair serves analogue equipment. Rated input level is 130 mV RMS, and the RCA input accepts up to 30 V at minimum volume with an input impedance of 20 kohm. Gain is 59 dB, maximum output voltage is 400 V RMS (1,130 V peak to peak) and the bias supply is DC 580 V. Harmonic distortion is rated at 0.025 percent or less from 1 kHz to 10 kHz when used with the SR-L series. The case measures 192 x 67 x 268 mm (width, height, depth) and weighs 4.5 kg.

Engineering and use context

Mains power reaches the circuit through an R-core power transformer, a type Stax chose for its reduced leakage flux. The cover is a 4 mm thick sheet of nonmagnetic aluminium. Signal strength is shown on a VU meter set into the front of the case. Consumption is 35 W, and the international version runs from 100 V to 240 V at 50 or 60 Hz. Stax specifies an operating range of 0 to 35 degrees Celsius at less than 90 percent humidity. The output is a single Pro bias socket, the 5-pin standard used by current Stax earspeakers.

Pairing

The rated distortion figure was measured with the SR-L series, which makes the SR-L500 MK2 and SR-L700 MK2 the most direct partners from the current range. The SR-L500 MK2 has an oval push-pull element with a rear open-air enclosure, weighs 351 g without its cable and uses a 2.5 m HiFC cable of copper with a small titanium content. The SR-003 MK2 in-ear model also fits through its own 5-pin Pro bias plug. For higher output, the SRM-T8000 uses E88CC dual triode tubes, reaches 470 V RMS and weighs 7.3 kg. A laptop can connect over USB, a CD transport or television over optical or coaxial, and a phono stage or tuner through the RCA pair, so one box covers both a desktop and a living-room system.

Alternatives

The Stax SRM-400S is an all-stage FET driver unit with RCA and XLR inputs, 60 dB of gain and a 3.4 kg case for owners who already have a separate DAC.