Stax SR-507 headphones and Stax SRM-727II headphone amplifier

Stax 507 + SRM-727II
Stax 507 + SRM-727II


I feel pleasure and awe in speaking of a product made by a headphones leader company worldwide. The Japanese Stax Ltd. was founded in 1938 and, fifty-six years ago, in 1959, it introduced the first model of electrostatic headphones: the SR-1, gone into production in 1960. I started to take an interest in the world of the sound playback in the ‘70s and I remember very well those “objects of desire” that resembled two small speakers to wear!

From the SR-Sigma, Stax has never abandoned the technical philosophy that corresponds to a clear design. It has been evolving in time and in the products until the new series Lambda, a line inaugurated more than thirty years ago with the SR Professional type. The current line includes the models SR-307, SR-407 and the Stax SR-507, object of our review. The imposing and elegant amplifier Stax SRM-727II belongs instead to the Stax High-End series.


Cuffie Stax SR-507 e ampli cuffie Stax SRM-727II



For a short introduction and some considerations on the electrostatic headphones, I suggest you to read the preamble of this ReMusic’s article of mine.

From the specs here, directly from the Stax website, we know that many new technological solutions have been used in the making of SR-507. For example, they use for the diaphragm a thin film of innovative techno-polymers that gives to the membrane a uniform movement and a high resolution of the sound message. The manufacture is sturdy, with materials of top quality. Very good are the pads, in genuine leather in the part in contact with the head and comfy to wear. Particular technological care has been put also in the connection cable and in the connector.

The powerful SRM-727 II, solid-state class A, on the front side, in the middle, has a big and heavy knob for the volume divided in two. It controls a double concentric potentiometer that, when needed, can balance the two channels. The on/off button and the outputs for two headphones complete the front side. On the back, there are two XLR balanced inputs and RCA unbalanced, selectable through a switch. Very useful is the parallel for the RCA inputs that retransmits the source signal towards another user, like an integrated amp or a console. Last, on the right down, there is the IEC socket for the provided mains cable. In the package, there is also a good RCA-RCA cable with golden connectors.


Pathos Aurium + Stax SRM-727I + SR-507 - KingSound M-20 + KS-H3


Headphone amp Pathos Aurium, headphone amp Stax SRM-727II and headphones Stax SR-507, headphone amp KingSound M-20 and headphones KingSound KS-H3: all in intensive run-in and in array by our Giuseppe Castelli

Listening impressions

Despite their design, wearing the SR-507 headphones is a pleasant experience. The shape of the ear pads hosts perfectly the auricles, the headband suits immediately to the dimensions of your head. Besides, it is not very heavy so you can have long hours of listening sessions. These merits help the listener to judge the quality perceived.

Remember: do not judge before a hundred of hours of functioning at least. Mostly the low range has to “mature” with a long run-in.

Then you can express yourself remembering the listening experiences you have made through the years. Ad example: at the Munich High End in 2015, I listened to the top range of Stax SR-009 and SR-007 MK2, amazing headphones, but too expensive at least for me! Considering the price of this SR-507, I must say that the quality is surprising.

No fear to rival the other headphones I told before. Just a slight lightness in the low frequencies, that improves after a long run-in. Everything else is of top level: maximum detail, wide soundstage, clear high frequencies but without listening fatigue, realist mid frequencies, just a bit unrefined on the voices, both male and female. Be careful: always ask yourself if this fault depends on the take! I repeat. These headphones have an excellent detail, so that any fault in the take comes out. I have always said that the electrostatic headphones, usually, are refined instruments that prefer refined musical contents, where the perception of the details and nuances is a priority with respect to other aspects of the sound message. I would not suggest the SR-507 to a disco DJ or to people that listen to music with low telluric frequencies and dynamics compressed only upwards. Said that, no fear for the musical genre: rock, jazz, classical, ethnic…if the takes are good, their value will be given back. After all, nowadays, thinking to a product that can satisfy only one genre or musical mood is commercially risky and, I would dare to say, useless too.

Let’s give credit where it’s due. The positive listening opinion I give would be different if the “engine” was not this powerful Stax SRM-727 II amplifier. Noiseless, refined, with a neutral tone and enough power to drive easily two electrostatic headphones.

A great match indeed.



In the last years, the heart of the lovers of the high quality headphones seems to be split in two: there is who loves unconditionally the electrostatic ones and never would betray them and there is who flutters his eyelashes at the dynamic headphones, better at the magneto-planar. From my part, I keep saying that it is not about the technical principle, but it is about the care, the innovation and the eureka moments of a designer. These Stax SR-507 driven by the amp Stax SRM-727 II make a successful product. Listen to them, if you have the chance and then…tell me!


Selection of listened music

Bryce Dessner - St. Carolyn By The Sea; Jonny Greenwood - Suite From There Will Be Blood - LP-2014

Chris Cornell - Higher Truth - LP-2015

Cincinnati Pops Orchestra - Orchestral Spectaculars, Erich Kunzel - Telarc CD-2002

Dave Matthews Band - Away From The World - CD-2012

Editors - In Dream - Deluxe Edition - CD-2015

Leonard Cohen – Popular Problems - HD Tracks 24/96 - 2014

Mozart - Requiem & Ave verum corpus - Riccardo Muti, BPO - Hybrid Stereo SACD

Mumford & Sons - Wilder Mind - LP-2015

Pink Floyd - The Wall Experience - CD-2012

Puscifer - Money Shot - CD-2015

Vangelis - Blade Runner Trilogy: 25th Anniversary - CD-2007




top score ✳✳✳✳✳ ReMusic Sparks

Tone: ✳✳✳✳ 1/2 | Neutral, but not aseptic. The quality of the take and of the source command.

Dynamics: ✳✳✳✳ | If you do not pretend a very high volume, where everything will be flattened, I’d say very well.

Detail: ✳✳✳✳✳ | There is all!

Versatility: ✳✳✳✳1/2 | The two headphone outputs, the balancing of the volume, the double input RCA/XLR and the parallel of the input signal /RCA, make this headphones/amp match very flexible.

Image: ✳✳✳✳1/2 | The virtual space around the pads is populated in a great way.

Aesthetic and functionality: ✳✳✳✳ | A classic Stax in the shapes without electro-mechanical indecisions.

Price/quality ratio: ✳✳✳✳ | Quite expensive the price of the SRM-727 II, even if it maintains all the promises of a classy apparatus. Very good the price of the SR-507. A best-buy for this category. Watch out for the offers!


N.B. The evaluation is referred to the match headphones SR-507 and amp SRM-727II



Official technical specifications

Electrostatic headphones Stax SR-507

Type: push-pull electrostatic, oval sound element, open-air back type enclosure - case

Frequency response: 7-41,000Hz

Electrostatic capacitance: 110pF including attached code

Impedance: 145kohm including attached cable, at 10kHz

Sound pressure sensitivity: 100dB/input 100Vr.m.s./1kHz

Maximum sound pressure level: 118dB/400Hz

Bias voltage: 580V DC standard

Right/left channel indication: "L" and "R" indicated on the arc assembly inside head spring, solid line (left) and dotted line (right) on cable

Ear pad: genuine leather - skin-touching portion, high-class artificial leather - circumference portion

Code: parallel 6-strand, 2.5m full length, low-capacity special wide cable, 6N(99.9999%) OFC with silver plating

Weight: 533g including attached cable, 388g without cable


Amplifier for electrostatic headphones Stax SRM-727II

Frequency response: DC-115kHz on SR-007 or SR-404, when using one unit

Rated input level: 200mV / 100V outputs

Maximum input level: 30V RMS / at minimum volume

Amplification: 54dB x 500

Total harmonic distortion: 0.01% / 1KHz, 100V RMS output on SR-007 or SR-404 Signature, when using 1 unit

Input impedance: 50Kohm / XLR balance 50Kohmx2

Input terminals: RCAx1 or XLRx1 balanced

Maximum output voltage: 450V RMS / 1KHz

Standard bias voltage: DC 580V

Power voltage: 120-240V +-10%, 50 to 60Hz, adjusted for your area

Power consumption: 46W

Temperature range for use: between 0 and 35C, max. 90% no condensation

External dimensions: 195x103x420mm (WxHxD) including VR knob and pin jack (20 + 10)

Weight: 5.2Kg


Official Italian dealer: to ProAudio International website

Official current price in Italy: SR-507 950.00 EUR - SRM-727II 2.450,00 EUR

Associated equipment: to Mauro Cittadini’s system



by Mauro
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