{"product_id":"stax-srm-400s-semiconductor-driver-unit","title":"STAX SRM-400S Electrostatic Headphone Amplifier","description":"\u003ch1\u003e\u003cstrong\u003eAll-stage FET amplification for STAX electrostatic headphones\u003c\/strong\u003e\u003c\/h1\u003e\n\u003cp\u003eThe STAX SRM-400S is a solid-state electrostatic headphone driver unit that succeeds the SRM-353X. Drawing on the design and manufacturing methods of the SRM-700S, it combines selected FETs throughout its amplification stages with a revised power supply and a more rigid chassis. RCA and XLR inputs connect your source, while a 580V DC bias supports compatible STAX electrostatic headphones.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eSelected FETs throughout the signal path\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eA custom low-noise dual FET handles the first amplification stage, with FETs also used in the output stage. STAX strictly measures and selects these components for their left- and right-channel characteristics, applying the approach used in the higher-end SRM-700S. This all-stage FET architecture supports high resolution and dynamic bass reproduction.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eDirect-coupled amplification\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eThe SRM-400S continues STAX’s tradition of complete DC amplification, with no coupling capacitors in the signal circuit. Its frequency response extends from DC to 90kHz when measured with one SR-L500 MK2, and harmonic distortion is rated at 0.01% or less at 1kHz with a 100Vrms output.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eA revised power supply for greater efficiency\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eThe newly-designed power transformer adds a dedicated winding for the low-voltage circuit alongside the high-voltage supply. This arrangement improves power efficiency and contributes to STAX’s stated improvements in sound quality over earlier driver units such as the SRM-353X. Power consumption is rated at 30W.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eA more rigid aluminum hybrid chassis\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eA revised hybrid chassis makes extensive use of non-magnetic aluminum. Its increased rigidity helps reduce the influence of vibration and other environmental noise factors on the amplifier circuitry.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eRCA and XLR source connections\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eConnect a source through the RCA or XLR input pair, using one input type at a time. RCA parallel outputs provide an additional connection to other audio equipment, and STAX’s concentric dual volume knob provides individual left- and right-channel level adjustment.\u003c\/p\u003e\n\u003ch2\u003e\u003cstrong\u003eBalanced sound across the frequency range\u003c\/strong\u003e\u003c\/h2\u003e\n\u003cp\u003eSTAX developed the SRM-400S to retain the resolution and dynamic low-frequency reproduction of its semiconductor amplifiers while refining the tonal balance of the SRM-353X. Designed to pair with the advanced Lambda series, it also offers an upgrade path for listeners moving beyond the driver unit in an SRS-3100 system.\u003c\/p\u003e\n\u003ch3\u003e\u003cstrong\u003eProduct highlights\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eAll-stage FET amplification\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eCustom low-noise dual FET input stage\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eStrictly measured and selected FETs\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eDC amplification with no signal-path coupling capacitors\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eRevised transformer with a dedicated low-voltage winding\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eRigid hybrid chassis using non-magnetic aluminum\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eRCA and XLR inputs, used separately\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eRCA parallel outputs\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eConcentric dual volume control\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003e580V DC bias\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003e\u003cstrong\u003eSpecs\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eType: All-stage FET DC amplification electrostatic driver unit\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eFrequency response: DC–90kHz, measured with one SR-L500 MK2\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eGain: 60dB\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eHarmonic distortion: 0.01% or less at 1kHz, 100Vrms output\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eInput impedance: 50kΩ RCA, 50kΩ × 2 XLR\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eMaximum output voltage: 400Vrms at 1kHz\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eBias voltage: 580V DC\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eOperating temperature: 32–95°F (0–35°C)\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eOperating humidity: Below 90%, non-condensing\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eInputs: One RCA stereo pair, one XLR stereo pair, mutually exclusive\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eLine outputs: RCA parallel output terminals\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003ePower consumption: 30W\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eDimensions: 7.68 × 4.02 × 14.80 inches (195 × 102 × 376mm), W × H × D, including protrusions\u003cbr\u003e\n\u003c\/li\u003e\n\u003cli\u003eWeight: 7.5lb (3.4kg)\u003c\/li\u003e\n\u003c\/ul\u003e\n\u003ch3\u003e\u003cstrong\u003eWhat’s included\u003c\/strong\u003e\u003c\/h3\u003e\n\u003cul\u003e\n\u003cli\u003eSTAX SRM-400S electrostatic headphone driver unit\u003c\/li\u003e\n\u003c\/ul\u003e","brand":"STAX","offers":[{"title":"Default Title","offer_id":67936237650156,"sku":"APS-1473-1","price":1299.0,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0225\/2721\/3642\/files\/NRE_SRM-400S.jpg?v=1793043039","url":"https:\/\/apos.audio\/products\/stax-srm-400s-semiconductor-driver-unit","provider":"Apos","version":"1.0","type":"link"}