Secrets of Home Theater and High Fidelity - Best of Awards 2020
Electrostatic headphones have always been looked at as the Holy Grail of headphone fidelity. Some upstart companies have jumped onto the Electrostatic bandwagon in recent years. STAX was there before any of them.

STAX SR-007A and Amplifiers with Headphones

STAX SR-007A Headphones Side View
STAX SR-007A

I got a chance to get up close and personal with various models of the STAX earspeaker line back at CanJam NYC earlier this year and each one of them had something interesting to offer. The SR-007A is the latest version of the SR-007 model which was introduced back in 1998 and updated in 2007. STAX sent along the SRM-700T (Tube) and SRM-700S (Solid State) earspeaker amplifiers for me to experience with the headphones and note any differences that I found.

Highlights

STAX SR-007A Electrostatic Headphone

  • Exceedingly Light and comfortable.
  • Rotating earcups are helpful to ensure good fit.
  • Sound quality was beautiful and completely effortless.
  • Bass was surprisingly deep and impactful.
  • Both amplifiers were of very high quality and they sounded different from one another.
  • They may ruin you for accepting anything else.
Introduction

Headband Close Up
Headband Close Up

When I was a teenager in Toronto I spent large portions of my summer free time hanging out in several of the city’s hi-fi shops. One of my regular audio haunts was Bay-Bloor Radio, and while I haven’t been back in years, at the time it was like the Grande dame of audio stores nestled right in the downtown core. I made a few of my formative audio purchases at that place; it just seemed to have everything that a budding audio-nerd could ever hope for. There was a variety of brands ranging from the attainable to the crazy obscure and expensive. And the staff graciously put up with, what to me, seemed like endless playtime in an audio candy store. In one corner I remember them having a dedicated headphone wall, laden with dozens of samples of audio ear wear for home hi-fi listening.

That is where I saw my first pair of STAX earspeakers. These were the rectangular shaped Lambda type and were unlike anything remotely resembling a headphone, at least to my limited understanding. I noticed they had their own separate amplifier, so you certainly couldn’t plug them into a Walkman. The thought of putting them on seemed dangerous. They seemed like some mad science experiment reserved only for the most serious of listeners. The fact that they weren’t even called headphones, but earspeakers was intimidating. I felt as if they were looking at me, sizing up my credentials and they concluded, “Don’t even bother kid, you’re not worthy yet”!

It wouldn’t be for another 5 years after that before I actually got to hear the old Lambda Electrostatics at an audio show. That’s when I really began to notice that, at the time, there were headphones and then there was STAX. Sure they were unwieldy, strange looking and power hungry. But nothing could seemingly touch the sound of a STAX electrostatic headset.

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So, many moons later, here I now sit with a set of handsome looking STAX SR-007A ear speakers and a pair of almost identical new headphone amplifiers, one tube and one solid-state. And gadzooks, the headphones are round! No matter, I got a sample listen of these fine transducers earlier this year at CanJam NYC and I immediately knew that I wanted to spend some extended time with them. My first long term exposure to electrostatic ear speakers, starts now!

STAX SR-007A Electrostatic Headphone Specifications

STAX SR-007A Electrostatic Headphone Specifications

Design:

Push-Pull Electrostatic Open-back, Over-the-Ear Headphones

Impedance:

170 K-Ohms @ 10 kHz

Capacitance:

94 pF (including cable)

Sensitivity:

100 dB / 100 V RMS @ 1 kHz

Bias Voltage:

580 V / DC

Manufacturer Freq. Response:

6 Hz – 41 kHz

Color:

Silver Earcups with Gold Accents and Black frame and padding

Weight:

365 grams (no cable)

Accessories:

2.5m 6-strand flat low-capacitance OCC copper cable with 5-prong electrostatic connector

MSRP:

$2,100.00

STAX SRM-700S/SRM-700T Electrostatic Headphone Amplifier Specifications

Design:

Solid-State (700S) or Valve (700T) Electrostatic Headphone Amplifier

Tubes for SRM-700T:

Two 6SN7 Type

Gain:

60 dB

THD:

less than 0.01% / 100 V RMS @ 1 kHz

Input Impedance:

50 K-Ohms (RCA) 50 K-Ohms x 2 (XLR)

Manufacturer Freq. Response:

DC – 100 kHz

Maximum Output Voltage:

450 VRMS (700S) 340 VRMS (700T)

Inputs:

One Pair of RCA and One Pair of XLR

Outputs:

One Pair of RCA (Rear) Two 5-prong Headphone outputs (Front)

Power Consumption:

46W (700S) 54W (700T)

Color:

Silver

Dimensions (W x H x D):

240mm x 103mm x 393mm

Weight:

6.3 kg (700S) 5.7 kg (700T)

MSRP:

$3,400.00

Company Directory:

STAX

SECRETS Tags:

stax, electrostatic, earspeakers, energizer, headphones, headphone review, amplifier review, review 2020

Design

STAX SR-007A Case
STAX SR-007A Case

Upon unboxing the STAX SR-007A, I was greeted with the most serious-looking of hard shell cases that I have ever come across. Once I was sure that there were no nuclear launch codes or classified documents inside the durable latched case, I removed the contents and gave them a closer examination. Unlike the STAX headphones (or “Earspeakers” for you purists) that I recalled from old, the SR-007A have round earcups mimicking the appearance of several open-back planar headphones that you are likely to see today. And while STAX still produces updated versions of the old style “Lambda” headphones, the SR-007A look decidedly more contemporary and less like you’ve strapped a pair of cheese graters or mini space heaters to the sides of your head!

STAX SR-007A Ear Cups
STAX SR-007A Ear Cups

STAX SR-007A Ear Pads
STAX SR-007A Ear Pads

STAX SR-007A 5-Pin Connector
5-Pin Connector

The SR-007A are eminently comfortable to wear. The lambskin covered earpads are large enough to completely encircle my earlobes and they, combined with the padded elastic headband and twin tension arms, made getting a good fit and seal quite easy. The earpads also rotate which allows fine tuning of the cord positioning relative to your neck and body. Clamping force against my head felt quite acceptable and the overall weight was a non-issue. The earcups themselves are made of a rigid and isolated resin so as not to induce any unwanted vibrations or resonances into the music. The cord is a wide, flat ribbon design that had some weight to it and took a little getting used to. It was terminated with a custom 5-prong jack that is exclusive to electrostatic headphones and plenty long enough to allow some freedom of movement.

STAX SR-007A Electrodes
STAX SR-007A Electrodes

STAX SR-007A In Use
STAX SR-007A In Use

Unlike dynamic driver headphones that uses a magnet and a charged coil to move a fixed point on a cone attached to a flexible suspension, or planar magnetic headphones that use a thin, vibrating conductive film suspended between two magnets, electrostatic headphone work on a bit of a different principle. An extremely thin diaphragm (typically an ultra-thin mylar film) is suspended between two conductive, perforated metal plates (electrodes). Once energized, the plates apply a static charge to either side of the film. By varying the electric field applied to the static charge, the diaphragm moves and generates sound. Remember, the film is said to weigh less than the surrounding air and nothing other than the fixed static charge comes in contact with it so the benefits are superb transient response, highly detailed reproduction and exceedingly low distortion across the audio bandwidth, even at higher SPLs. What electrostatic headphones are not known for is for having a noticeably punchy bass response. STAX claims that by having no perforations on the outer periphery of the electrodes it uses in the SR-007A, allows for an improved level of drive force that is applied to the diaphragm which results in better bass response.

SRM-700T and 700S Amplifiers
SRM-700T and 700S Amplifiers

SRM-700T Top Vent
SRM-700T Top Vent

SRM-700T and 700S Amplifiers Back
SRM-700T and 700S Amplifiers Back

What also sets electrostatic headphones apart is that they require higher voltages to work, and this is where a suitable dedicated amplifier is mandatory for the headphones to operate correctly. Not just any headphone amplifier will do however, it must be expressly made for an electrostatic headphone’s higher power demands. STAX graciously sent along both versions of their new SRM-700 series amplifiers for me to experience. The 700S is the solid state version while the 700T is the tube variant. Both look and feel essentially the same in their serious yet understated way, save for the 700T having a different top cover with two large dimples and vents that allow you to bask in its warm tube glow. The volume control on both units has that nice weighted travel that you associate with a premium piece of audio equipment. The 700T, upon powering up, flashes its power light for about 30 seconds before remaining solid indicating that it is warming up the tubes prior to allowing you to listen. It uses a pair of Tung Sol 6NS7 tubes that come pre-installed in the unit. The 700S obviously is tube-less and starts up instantaneously once the power button is pushed. It also puts out more output voltage than its tube counterpart (450 VRMS vs 340 VRMS) not that the voltage difference made any sort of impression during my listening. On the backside there are both XLR and RCA inputs, along with a dial that selects which one is monitored, a set of RCA outputs, and a dial that allows you to bypass the internal volume control and use either unit as strictly amplification should you wish to use a different preamplifier for volume control. There is also a ground lug which I assume is for a turntable

Setup

Main Listening Setup
Main Listening Setup

For this review, the STAX SR-007A headphones and both amplifiers were connected to the Audio-gd AS-1 DAC which was fed music files (via USB) from my Surface 3 PRO tablet. The tablet runs ROON to manage all my local digital music files along with online streaming via Qobuz.

In Use

In my second career as a “professional reviewer” (I use that phrase half-sarcastically) I’ve devoted a fair amount of time and effort in sampling all manner of headphones and learning more about how they work and how they are developed. I am still very much far from an expert on the subject but I genuinely love headphones and for the longest time I’ve appreciated how they can draw me into the music, in a way that loudspeakers just can’t. Of course, wonderful sounding loudspeakers in a good room have their own charms but with headphones, it’s simply about me and the music. And good headphones can very much transport you away like few other things out there. In my view anyone who is serious about their music should have as good a pair of headphones as they can find/afford whether they are for home or mobile use.

Conducting this review has only cemented my initial conclusions that there is something very different about the way electrostatic headphones sound when compared back-to-back with the best dynamic or planar-magnetic designs. There is an effortlessness in the way that they present music that other types of headphones can’t quite match. Really good planar designs can get close and dynamic driver headphones can have advantages in bass impact, but a really good electrostatic headphone seems to be on another level. It is going to sound slightly corny saying this, but other types of headphones sound like they are playing back music whereas electrostatic headphones just sound like…well… music.

The STAX SR-007A quite simply are a stellar sounding pair of headphones. Better that the best planars that I’ve heard and better than the best dynamic cans too. As cliché as it sounds, they really do just get out of the way and let you enjoy what you are listening to, utterly and completely. The effortlessness of their sound must be attributed to the way the electrostatic transducers inherently work and yet I believe the utter lack of distortion across their operating bandwidth is another important reason. When I compared them to the Focal Stellia and the HiFiMAN HE-1000v2, top notch dynamic and planar designs respectively, I wasn’t entirely prepared for the type of difference that I heard. Both the Stellia and the HE-1000v2 sounded extremely good, the HiFiMAN with its big, fun yet detailed sound, while the Stellias excelled with their balance and bass impact. Switching to the STAX was like getting the best of both the other two headphones but with a sense of effortless sound and transparency that surpassed the others, by a noticeable margin. The SR-007A had an exceptional balance to their presentation, details did not sound overly exaggerated, nor did they have that thinness to their sound that the HiFiMANs can exhibit with some kinds of music. I also wasn’t expecting to be wowed by the bass response of the SR-007A but the STAX surprised here having at least the equal impact of the Focals in the bass department. But here again the clarity and lack of distortion in the bass response of the STAX just made the sound of low organ notes, tympani hits and acoustic double-bass sound that much more enjoyable. I always keep coming back to the word effortless but that’s as best a term as I can come up with to describe what I hear with the STAX. One really needs to listen to the SR-007A to understand what I’m trying to get at but there is a very real danger of being ruined for anything else once you do take that listen. And while I wouldn’t say that the STAX are completely ruthless to less than perfect recordings, they will let you know when something on your playlist is “not up to scratch”.

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The SRM-700S and 700T amplifiers are both beautiful to look at and to use when powering the SR-007A. The STAX representative I spoke with was curious to know if I would notice any sort of difference between the sound signature of both amplifiers, one being solid state and the other tube. Both amps powered the headphones more than capably. Raising the volume knob to the 12 o-clock position got the SPLs to the point that I could barely stand the volume. Still clean and clear but very, very loud. Parking the knob at 10 o-clock was a comfortable spot for my listening time. True to what I expected, the 700T had a slightly fuller sound from the upper bass and through the midrange. The treble was nice and detailed but also a little softer around the edges compared to the 700S. I found it particularily enjoyable to listen to Jazz, acoustic Blues, and older recordings on the tube amp. Overall, it had a nicely judged character to its sound as opposed to an overly tube “bloom” that I have heard from some other tubed headphone amps. The 700S meanwhile was linear, transparent and very revealing. Everything sounded quite balanced and the treble was fully formed and detailed. I felt that both amps had a pretty much equal handle on the bass frequencies, I couldn’t pick out one amp as being noticeably superior than the other in that regard. I enjoyed the opportunity to experience both amp designs. If I had to pick one for my own needs it would have to be the solid state SRM-700S. I ended up alternating between the 700T for “fun listening” and the 700S for “critical listening” in most cases, but that is just a reflection of my personal tastes.

Some of the music that I enjoyed with the STAX SR-007A was:

Rimsky-Korsakov, Scheherazade

Rimsky-Korsakov, Scheherazade, Mario Rossi Conducting, The Sea and Sinbad’s Ship, Vanguard Records, 1956, FLAC 16/44.1.

An old recording but handled well particularly with the STAX headphone and tube amp combo. Listening through the SR-007A, the performance had a surprisingly deep and wide image for this music’s age. The entire rendition seemed lighter than air and everything just flowed. Strings were airy and full of detail. Woodwinds and flute had wonderful character for the vintage of this recording. I was worried that the STAX would be so revealing as to make this older version of Scheherazade sound thin and brittle, but the SR-007A and the SRM-700T combination was quite magical with this. The 700S solid state amp handled this track well also, but this was one of the few occasions that I preferred the sound of the tube amp outright. There are certainly cleaner and more modern recordings of Scheherazade out there but this performance of it is a favorite of mine, minor warts and all.

Joe Bonamassa, Redemption

Joe Bonamassa, Redemption, Ghost of Macon Jones, J&R Records, 2018, Streamed via Qobuz.

A modern blues recording with an extremely dimensional presentation. The big deep image was especially effective on the “Ghost of Macon Jones” given the song’s story. The SR-007A’s reproduction is layered, detailed and outstanding. Every nuance of JB’s electric guitar, its tone, sustain, distortion and overdrive comes out clearly. Nothing muddy at all to the sound. Joe Bonamassa and guest vocalist Jamey Johnson singing harmony together, as played through the SR-007A, had a very in-the-room feel. The 700T tube amp was a little more meaty in the upper bass and polite in the highs with this track. The 700S solid state amp had a more crisp and detailed treble and good solid bass and balanced midrange. It was the solid state amp for me on this one.

Melody Gardot, My One and Only Thrill

Melody Gardot, My One and Only Thrill, Who Will Comfort Me, Verve Records, 2009, FLAC 16/44.

The finger snaps that start at the song opening sound crisp and just float in space while reverberating through the STAX headphones. Tonally, Gardot’s voice is soulful, clean, and nicely reproduced with every nuance and breath revealed by these headphones. The muted trumpet in the track also sounded just right, sharp and expressive but not abrasive. The SR-007A also give a nice weight and punch to the acoustic bass lines making them easy to follow and giving the song a good foundation. Listening to this track through my HE-1000v2 or the Focal Stellias is like I’m listening to a really good performance reproduced very well. The STAX make me feel like I am AT the performance.

Billy Joel, The Stranger

Billy Joel, The Stranger, Vienna, Columbia Records, 1977, 16/44 FLAC.

I know this song backwards and forwards as it is probably my favorite Joel composition. The STAX made Joel’s piano come positively alive with the ring of the notes and the echo from the recording studio. Drummer Liberty DeVitto’s cymbal fills sounded absolutely real with a great sheen to them. His entire drum kit was nicely reproduced actually, with a solid weight to the kick drum and good detail of the drum skins coming through. Joel’s voice was nicely centered in front of me with great tone and the familiar accordion solo sounded just right with its harmonica-hooked-to-some-bellows tone. I preferred the solid state amp’s handling of this tune as well.

Conclusions

STAX SR-007A and Amplifiers with Headphones
STAX SR-007A and Amplifiers

The STAX SR-007A and matching 700 series amplifier provide the serious headphone enthusiast with a reference level home listening system. Outstanding!

Likes
  • Effortless musical reproduction from top to bottom.
  • Light and comfortable to wear for extended periods.
  • Amplifiers are well made and perform flawlessly.
  • Choice of amps. Tube or not to tube?
  • They sound unlike anything else.
Would Like To See
  • A set of balanced outputs on the amp.

In my conclusions, especially as I get older, I try to avoid heaping superlatives when I review a product that I genuinely like because I never know when that next better product will come along and take me by surprise. However, I’m finding it really hard not to just openly gush about the STAX SR-007A and both of the SRM-700 series headphone amps. Yes, it is a roughly $5000 dollar personal listening set and you may be saying, A- That’s crazy! Or, B- Well it’s $5000 dollars and who wouldn’t rave about a personal toy that cost that much? Both would be missing the point. Electrostatic headphones sound like nothing else out there and anyone who is serious about their headphone listening should experience a pair for themselves to understand what I mean. The STAX SR-007A themselves hit that sweet spot for me in terms of comfort and performance unlike anything else, from a headphone standpoint, that I have experienced thus far. They produce pure, weightless musical energy seemingly devoid of distortion and effort and at a volume that can well surpass reasonable need. And they produce all the bass I could want in the bargain. Combined with either one of the STAX SRM-700 amplifiers, one is presented with a reference level home listening setup that could ruin a person to accept anything less. Is there something better out there? Perhaps, but I’d wager not without a significant increase in cost and for an incremental gain at that. If budget were not an issue I would purchase these outright and use them as a reference. I find them to be outstanding in every regard and that I had every right to be in awe of their ancestors in my youth.