Stax SR-X MK3 Vintage Headphones and SRD-7 Amp

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General:

From the one and only Ken Rockwell @ kenrockwell.com:
These Stax SR-X Mark 3 electrostatic headphones are decades old, and still outperform conventional dynamic headphones like the Sennheiser HD 800 and Ultrasone Edition 8 in most ways, especially for clean, open, natural sound. Better, these Stax headphones, used, sell for one-tenth the price.

When introduced in 1975, these Stax SR-X Mark III were the world's highest performance headphones, unchallenged until Stax introduced the even more exotic SR-Sigmas in late 1977.

These are not ordinary headphones that use a coil of wire inside a magnet glued to a heavy diaphragm, like mass-market products from Sennheiser, Ultrasone and Beyer.

These are electrostatic headphones. Electrostatic technology is far superior for reproducing sound.

Comparing the performance of one completely different technology to another, like electrostatic to dynamic transducers, is like comparing the speed of a bicycle to the speed of a car. Even if you've got a brand-new million dollar bicycle, my beater 1974 slant-six Plymouth Duster goes a lot faster and farther.

This Stax SR-X Mark 3 may look like something pulled out of a WWII Japanese submarine, but its proven electrostatic technology excels at super-low distortion and freedom from any resonance or coloration.

These headphones win on subtlety. If you want to enjoy every nuance of your music over hours and hours of careful listening, these are your headphones. If you prefer something that boosts everything for an impressive 30-second demo blast, these aren't.

Stax invented electrostatic headphones in 1959, and had 16 years of experience optimizing them when these were introduced. Stax' marketing people have always called these "earspeakers" instead of headphones.

These SR-X Mark III aren't that much different than the previous SR-X headphones, and look similar to a black version of Stax' very first SR-1 of 1959. Honestly, the Stax New SR-3 (1971-1975) are more different in looks than in actual performance from these newer SRX-IIIs.

While Stax' newer and better headphones went to rectangular housings and elliptical drivers with the SR-Sigma of 1977 and continue to this day, Stax' top-model Omega introduced in 1993 was round again, and to this day, the round SR-009 of 2011 is Stax' very top $5,000 model. Maybe there's something to be said for round drivers?

Brand Background:

Stax, making the worlds best electrostatic headphones since 1959.

Ownership:

Single Owner

Connections:

Speaker level inputs.

The speaker input cables have been modified. The cabling looks to be from Cardas based on our experience. 

General Sound:

Smooth, uncolored, undistorted natural and clean.

Cosmetic Condition:

7 - Some Wear and Light Scratches https://skyfiaudio.com/pages/our-rating-scale

Working Condition:

Working perfectly and tested in our lab.

Included:

As pictured.

Packing:

Will be packed using our highly developed in-house process and custom packing materials.

Weight:

10.0

Age:

1979

Reviews:

https://www.kenrockwell.com/audio/stax/sr-x-mark-3.htm

Testing Process:

Tested in our lab with both the headphones and included headphone amplifier working as they should.

Specs:

Input

Connects to any Stax standard (230 V bias) 6-pin adapter, energizer or amplifier.

Won't connect to any Pro or Professional (580 V bias) 5-pin adapter, energizer or amplifier.

Cord

Straight, supple black cloth-covered round cord.

The red blip is the right channel.

2.5 meters (8 feet) long.

Soft, about 6mm (1/4") diameter, measured.

It's a much better cable than the cheap plastic cable of the Ultrasone Edition 8. It feels just like the cable of the Sennheiser HD 800, however this Stax cable has the same microphonics as most cables, not the mysteriously silent cable of the Sennheiser HD 800. ("Microphonics" mean that if you rattle the cable against something, that the sound is transmitted mechanically through to the headphones.)

Diaphragm

2 microns thick.

For comparison, a very thin dry-cleaning plastic bag, the type that blows away just by breathing on it, measures about 20 microns!

Plate Spacing (electrode gap)

300 microns.

Capacitance

120 pF.

Impedance

130 k Ohm at 10 kHz.

Frequency Response

30 - 25,000 Hz, rated (tolerance not stated).

Stated elsewhere as 20 - 70,000 Hz, unstated tolerance.

Sensitivity

97 dB SPL with 100V RMS input at 1 kHz, 230 V bias.

Maximum Output Level

110 dB SPL, 230 V bias.

Stated elsewhere as 115 dB.

Headphones Weight (actual measured)

10.2 oz. (290g), without cord.

12.590 oz. (357.0g), with original cord and plug.