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STAX is proud to introduce a new semiconductor driver unit SRM-400S as the successor model of SRM-353X. A STAX custom-made low noise DUAL FET is installed on First Stage and additional FETs are also installed on last stage. SRM-400S follows the design and the manufacturing method of the high end model SRM-700S, in which the amplifier high quality FETs are installed in all stages. The characteristics of the right and left FETs are measured strictly and the selected FETs installed in 400S are also featured in SRM-700S. In addition to the conventional power transformer for the high voltage circuit, the newly designed power transformer with winding for a low voltage circuit is installed in SRM-400S. The low voltage winding enables to improve the power efficiency and achieves further power saving and better sound quality than what was featured in older driver units such as SRM-353X.
The new chassis which is more rigid than the conventional model is installed. The chassis has a hybrid structure using a lot of non-magnetic aluminum and further reduces the effect of the environmental noise factors such as vibrations. The custom made concentric dual volume knob which is common to STAX products and RCA PARALLEL OUT functions are installed same as the conventional driver units. All electric components are strictly selected considering the environment.
SRM-400S presents the high resolution sound which is unique to the semiconductor circuit design and dynamic low range sound reproduction. From the lows to the highs, the frequency response is well harmonized throughout the entire spectrum. Not only for the combination with the advanced lambda series, SRM-400S is also ideal for the upgrading from the entry level SRS-3100. This is a promising new model which covers beginners to intermediates among the renewed driver unit line-up.
• All-stage FET Configuration DC amplification
• Newly Designed Output Stage
• Custom-Made Low Noise Dual FETs
• Pair of RCA input terminals
• Pair of XLR 3-pin input terminals
• RCA parallel output terminals
• 30W Power Consumption
Frequency Response :DC - 90kHZ (with one SR-L500 MK2)
Harmonic Distortion :0.01% or less (1kHZ/100Vrms output)
Maximum output voltage :400Vrms (1kHz)
Bias Voltage :DC 580V
Operating Conditions :32 to 95 degrees fahrenheit @<90% humidity
Dimensions :(H)4.0" x (W)7.68" x (L)14.8"
Weight :3.4 lbs
Overall rating: 4.75 / 5 from 4 reviews.
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"Disclaimer: these are my first electrostatic system; and I don't see any reason to invest more. I got the SRM-400S with the SR-L700 MK2, and they are simply amazing. I can now understand what people call endgame. Every detail on every music is just there, ready to be picked. Also, I got them both open box, with absolutely no difference from brand new ones, except for the packaging. 100% worth it."
"Good unit"
"This is my third Stax amplifier. Like my two previous Stax amps from 1982-1986 (SRM-1/Mk2 Pro, SRA-14S) that are still fully functional and in use today, the SRM-400S puts a smile on my face to see and hear “Made in Japan” quality workmanship continue in their current products. Worthy improvements are the larger volume control knob, addition of XLR balanced inputs and a second Pro-bias earspeaker output. I appreciate Stax continuing with the ganged left-right channel volume control to allow for correcting channel imbalance of the input signal or imbalance of the earspeaker drivers. As expected, the SRM-400S sound is neutral, and there is no discernible noise or distortion at zero to very high gain. There is no power-on or power-off pops/thumps from the earspeakers. The SRM-400S has plenty of gain to drive my Stax SR-Lambda Pro, SR-507, SR-L700 Mk2, and Hifiman Jade II earspeakers. Volume control setting between 10-12 o’clock position gave more than sufficient gain to drive and reveal the sound signatures of these earspeakers. The SRM-400S effortlessly brings music to my ears. Well done again Stax!"
"Nice upgrade from SRM-252S. More bass, dynamics and clarity! Admittedly the SRM-252S isn't bad if that's all you can afford: but the increased power/volume capability of the SRM-400S is audibly better. The only downside of this and any full-size electrostatic amplifier is the size: They take up about 17" depth with cables, which means they take up a lot of your desk or even studio rack."
