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Review: Stax SRM-700T & SRM-700S – World-class Twins

Review: Stax SRM-700T & SRM-700S drivers are world class and hard to top for me when used with the Stax SR-007MK2, SR-009 and SR-009S headphones.

Review: Stax SRM-700T & SRM-700S – Some brands in the hi-fi world today have ‘legendary’ status. Often they have been around for a long time, have developed a special technology and further improved over the years, or have always excelled in unique craftsmanship in production. Not infrequently they are smaller manufacturers, more focused on evolution than on revolution, and a tad conventional. Think, for example, of SME, Leben or Quad. Dangerous for the audio enthusiast, because you can fall in love with it for a lifetime. Stax also belongs in this list. The ‘earspeakers’ and ‘drivers’, which already had their origin in the fifties of the last century.

Looking back on my development steps in the hi-fi field, I can say that in the initial phase, from the mid-seventies, these were significantly influenced by at least two people. First of all by Henri van Hessen of the then TransTec and importer of Quad and KEF. As a young music student, I occasionally entered the building on the corner of Witte de Withstraat in Rotterdam, because of my interest in hi-fi equipment. During my education at the Rotterdam Conservatory I often worked with Akai and Sony open reel recorders with built-in speakers and simple microphones. The sound results were not always great quality. Noise and distortion were often standard, something I had a hard time living with even then. It was therefore not surprising that a few years later I had Quad ESL-63 electrostatic loudspeakers and KEF 104-2. But a second person really introduced me to the electrostatic phenomenon for the first time: the illustrious John Snijders of Snijders Hifi on the Hoogstraat in Rotterdam. I’ve been there every week for years. He knew that I studied classical music and was also interested in open reel. I can still hear him say: “Listen to something decent for once”. And he demonstrated to me the Stax SR-40 ‘Electret Earspeakers’ with accompanying SRD-4 adapter. I can still remember the first listening session in his shop, occasionally interrupted by a train speeding by on the iron railway viaduct located right next to the shop. And later John also introduced me to the Revox B-77 open reel recorder (“you have to choose 2 tracks!”). The start of a serious hi-fi foundation. And now, more than forty years later, I am still a ‘heavy user’ and Stax enthusiast and I still have a Revox C270 and several PR99’s running at my home.

Stax at home through the years

Since that first Stax set, I have grown along with the development of new Stax models and, until today, I have also started to use them for professional use. I’ve lost count of the sets, but around 1980 I bought the first SR-Labda and SRM-1 ‘driver unit’. The latter was a big step forward. My old SRD-4 still had to be connected to the speaker outputs of my amplifier, while the SRM-1 could already be connected to tape out with an RCA cable and had connections on the front for normal and pro bias (more on that later). Over the next few years, new Labda models came to my house until I finally made the move to the SR-007MK2 and SR-009, both powered by the Stax SRM-007tII valve amplifier.

Stax SRM-700T & SRM-700S- How does an electrostat work? 

Conventional headphones use small loudspeakers: a copper coil and a magnet in which the coil moves through the music signal. The whole is attached to a cone, which is set in motion and produces sound. The operating principle of an electrostat is completely different. Sound is created because air is set in motion by the attraction or repulsion of a wafer-thin electrostatically charged membrane. This polymer membrane, many times thinner than a human hair, is clamped between two perforated metal grids (plus and minus) and therefore remains well balanced. In order to have sufficient electrostatic voltage, a high voltage converter is required, an ‘energiser’ or ‘driver unit’. This produces approximately 580 Volts of bias (polarization) voltage. The mass of an electrostatic diaphragm is considerably lower than that of a conventional speaker and therefore has a major influence on the sound reproduction, which in terms of frequency range goes far beyond the limits of human hearing. In the past, Stax produced headphones with a 230 Volt bias, but later switched to 580 Volt on the Pro models, because this gave more dynamics.

Around 1992, Stax stopped producing 230 Volt models. And don’t worry, the high bias voltage on your head is completely safe, if you handle the Stax with care (but this applies to almost all hi-fi equipment). You have to handle an electrostat with care. They are sensitive to dirty air (smoking!), dust and especially moisture. I once witnessed a Stax owner who, in a thoughtless moment, blew hard into one of the pinna of his Labda, damaging the diaphragm beyond repair. If you use them carefully, they will last a very long time.

Stax is happily (!) conventional

Japanese recording engineer Naotake Hayashi founded Showa Ko-On Manufacturing in 1938 and renamed it Stax Industries in 1952. He designed the world’s first electrostatic headphones in 1959, which came on the market in 1960 as SR-1. To this day, Stax calls its products ‘earspeakers’, rather than headphones. This is said to be because in the early days the high quality of Stax could only be compared with the very best speakers of the time, and not with headphones. Although that’s a bit nonsensical today (there are several top-class and much more expensive headphones out there) the designation has become somewhat part of Stax’s conventional stance. It has cost them dearly in the past. Stax has always been a small manufacturer in terms of size, but in the past, in the ‘golden Japanese hi-fi period’, it has also ventured into the production of pre- and power amplifiers, turntable elements and arms, dac, full range electrostatic speakers and a CD player. Since everything was built with the highest possible quality and in small series, this invariably resulted in economic problems. In 1995 Stax went bankrupt and in 1996 makes a modest restart, but with few resources for expensive research, This invariably resulted in economic problems. In 1995 Stax went bankrupt and in 1996 makes a modest restart, but with few resources for expensive research, and that in an environment where competition is increasing. Moreover, they adhered tightly to ‘made in Japan’ as part of the philosophy and the highest possible quality. I remember that as a Stax enthusiast I then held my breath when I heard in the press in December 2011 that Stax had been taken over by the Chinese Edifier Technology.

Stax SRM-700T & SRM-700S – Congratulations to Edifier

But that acquisition has worked out really well to this day, and I can’t help but commend Edifier’s management for the way they deal with Stax. First of all, Edifier ensured that Stax could have a modernized work and test environment. In addition – to my surprise – ‘made in Japan’ has been maintained as part of the quality philosophy, a substantial research budget has been made available and Stax can carry out the product development autonomously. With only a small team (approximately fifteen permanent employees!) Stax builds by hand as before and many new products have been able to leave the factory in recent years.

And gradually, perhaps at the hand of Edifier, you also see some subtle marketing changes at Stax. From 2011, the SR-009 headphones appeared, then modernization of the entire Labda series, in 2017 the top-class SRM-T8000 driver with tubes and then in 2018 the SR-009S. If you now visit the official website of stax (www.stax-international.com) you will see for the first time that Stax is clearer in the indication of the levels. For example, the SRM-700S and Stax SRM-700T drivers are now clearly classified under ‘high-end class’ and, for example, the brand new drivers SRM-400S and SRM-500T are placed under ‘middle class’. The ‘Pro’ designation from the past, which indicated the highest level, will not return.

Stax SRM-700T & SRM-700S – The influence of the driver on the sound quality

This article focuses mainly on the drivers, and for good reason. In the early days of electrostatic headphones, the driver was mainly intended to produce bias voltage. However, over the years these were refined and the sound quality was increasingly realized not only through the design of the headphones, but through the driver, which became available in later years in both transistor and tube versions. Again, because of the subtle display differences. Whoever chooses Stax can actually make many combinations between the different drivers and headphones. Logically, you also combine high-end levels such as the SR-007MK2 and SR009(S) with drivers at this level.

I must say that for many years I have had the pleasure of using both the SR-007MK2 and SR-009 with an SRM-007tII driver/tube amplifier. It is noticeable that the former headphones require slightly more power to reach the top level than the SR-009, but the SRM-007tII can handle both very well, even at high volumes. I’ve never in my life heard a speaker system that comes close to the sound quality of these combinations, and that includes conventional headphones (although the Focal Utopia comes pretty close). During the introduction of the – otherwise very expensive – SRM-T8000 driver I had the opportunity to listen to it extensively. With much more power than before and even equipped with a later – so future-oriented – slot at the rear. Stax takes the time for everything, because more than four years after its introduction, no interpretation is offered for this slot. I was very impressed with the sound at the time and its introduction was certainly also Stax’s response to wishes from the hi-fi world to drive the Stax headphones with more power, for even more dynamics. These sounds came mainly from the corner of the so-called ‘Stax Mafia’.

The Stax Mafia

Well, that (mostly American) Stax Mafia (the name has become a nickname) and everything around it is a group of remarkable enthusiasts who often criticize the technical design of the Stax drivers, the parts used and you name it. See all forums on the web! Over the years, this has resulted in several small manufacturers who themselves produce ‘much better’ amplifiers for Stax headphones than Stax believes they can do themselves, often at cost prices of many thousands of dollars. I never understood this from my hearing. Over the past two decades I have been able to listen to these amplifiers several times. Sometimes they gave a lot of power, others hummed so loud that you could already hear them in the next room and some tube variants produced so much heat that a central heating system in the room was not necessary. And how did it sound? In demonstrations they happily showed at very high volumes (very harmful to your hearing) how good it all was, often with a sound image that was pumped up too clearly for my taste. That is why I am glad that Stax has remained so conventional and has also kept good ears and attention to subtlety in the sound reproduction.

Stax SRM-700T & SRM-700S

The new SRM-700S and Stax SRM-700T

Recently Stax introduced two new drivers: the SRM-007S and the SRM-007T. They are almost identical in appearance. The T has two recesses at the top, under which tubes betray themselves and when switched on, an orange LED first flashes for some time to warm up the tubes. The S does not have those recesses at the top and a blue LED immediately lights up when it is switched on. Both versions also have two headphone connections on the front (580 Volt polarization voltage) and a choice to block the two-way volume knob. In addition, there are LEDs that indicate whether or not there is by-pass of the volume knob and choice of inputs. The back of both devices is identical. We see selector switches for the inputs (1x XLR, 1 x RCA, where the RCA also has a parallel out function) and for internal or external (bypass) volume control. An earth connection is also available. The dimensions of both devices are the same (240 x 103 x 393 millimeters), the weight differs slightly (the S 6.3 kg, and the T 5.7 kg). Both have a frequency range of up to 100,000 Hz, the maximum output voltage differs: 450 Vrms (1Kz) for the S and 340 Vrms (1Kz) for the T. The price for both devices is also the same (Ä 4.190,-), a lot more than that of their predecessors. The exterior is beautifully finished, of the highest level. the maximum output voltage differs: 450 Vrms (1Kz) for the S and 340 Vrms (1Kz) for the T. The price for both devices is also the same (Ä 4,190,-), a lot more than that of their predecessors. The exterior is beautifully finished, of the highest level. the maximum output voltage differs: 450 Vrms (1Kz) for the S and 340 Vrms (1Kz) for the T. The price for both devices is also the same (Ä 4,190,-), a lot more than that of their predecessors. The exterior is beautifully finished, of the highest level.

There are more differences under the hood, which are also reflected in the sound character. Both have low noise FET in the first amplifier stage but the S has J-FETS in the second amplifier stage, while the T in the second stage uses two 6SN& tubes and non-inductive winding resistors from Vishay Co.

The listening test of Stax SRM-700T & SRM-700S

Both the S and the T have been listened to extensively for a long time in combination with an SR-007MK2, an SR-009 and SR-009S. Both drivers were connected via Siltech Anniversary 550i RCA cables to a Mark Levinson No. 585 integrated amplifier, using an Esoteric P-05 SACD VRDS Neo5 drive and D-05 dual 32 bit DAC combination as the source.

The first general impression is that both the S and T make a statement in the Stax sound reproduction. Although they appear to be twins, the differences, although not very large, are still very noticeable. The listening test also yielded a surprise. While I can’t fault the playback quality of the SR-007MK2 with the Stax SRM-007tII, these headphones with both the S and T delivered a soundstage of supreme transparency with an almost sensational bass response, especially with the S. listening to the sacd Lyn Stanley Live at Studio A (ATM 3109) at track 3 Route 66 the pluck bass went right through my chest. Much fuller than with the old driver but also with the feeling that there was more than enough power to make the SR-007MK2 shine. The SR-009 showed a beautiful sound image in the full width with both drivers. And oh, how quiet those S and T are! Incredible. As reviewers we sometimes talk in terms of ‘deep black silence’, but you really have to experience this to believe it. And what I already expected, the SR-009S then provides the most ultimate listening experience. I think these headphones with the S of T can produce about the best sound available in the hi-fi world and on the border of what is technically feasible today. You can understand why Stax has been given the status of ‘legendary’ in recent decades. the SR-009S then provides the ultimate listening experience. I think these headphones with the S of T can produce about the best sound available in the hi-fi world and on the border of what is technically feasible today. You can understand why Stax has been given the status of ‘legendary’ in recent decades. the SR-009S then provides the ultimate listening experience. I think these headphones with the S of T can produce about the best sound available in the hi-fi world and on the border of what is technically feasible today. You can understand why Stax has been given the status of ‘legendary’ in recent decades.

Wide deep stage and precise placement

Both the S and T provide a very wide and deep stage with incredibly precise placement of instruments and voices. To this extent this seems to me unfeasible with loudspeakers.

On the audiophile CD Lucent Waters by jazz pianist Florian Weber (ECM 2593 6751588), Weber plays with his jazz combo almost whisper-quiet pianissimo fragments, in which the percussion is only touched with the slightest touch. You see the combo. You see everyone playing. You also hear the whole. The percussionist sits to the left of the pianist. The strings of the pluck bass sometimes gently touch the fingerboard, with a subtle sound. All three headphones score superbly here.

The differences

But what are the subtle display differences between the S and T with the three headphones? For this we go back to a SACD as a source. Violin Concerto No. 1 by Karol Szymanowski, played by Tasmin Little with the BBC Symphony Orchestra (Chandos CHSA 5185). This recording is one of the best SACD discs I know and played top notch as well. The orchestral image, with a lot of small percussion and a lot of movement, with the violin solo falling in a high register, is presented crystal clear by the S, with the greatest possible purity. But on all three headphones you can hear triangles, bells, gongs, the high violin string positions and the string sessions taking on a golden sheen, a little more warmth than the S. And when you listen to the double basses, the S is subtly slightly fuller than the T.

The same heat difference, because that is what it is, can be seen on the BIS SACD Il Labirinto Armonico, with three violin concertos by Pietro Locatelli (BIS 2445). Ilya Gringolts interprets the difficult to play passages with great passion and luckily not too neatly. Both the S and T make all kinds of noises audible in the recording through the three headphones: a snorting Gringolts, a soft cough from one of the musicians, the turning of sheet music or sliding music desks and chairs. And again: the tones of the harpsichord and the solo violin are slightly more golden and warm with the T than with the S. The combination Stax SRM-700T and SR-009S is the best in my opinion.

Stax SRM-700T & SRM-700S – Practice

I also use the Stax headphones professionally. When preparing for a concert, especially in a large space like a church, I often use a Sony PCM-D100 during rehearsals to make some test recordings in DSD, which allows the acoustics and balance between solo violin and accompaniment to be checked and listened to at home, even apart from technical review of the game. I also tried the S and T for that. Even the smallest nuances and idiosyncrasies of my Guarneri violin are reproduced very accurately.

Conclusion –  Stax SRM-700T & SRM-700S

The Stax SRM-700S and Stax SRM-700T drivers are world class and hard to top for me when used with the Stax SR-007MK2, SR-009 and SR-009S headphones. I especially found the enhanced performance of the SR-007MK2 surprising with these drivers, a model that has been in production since 2007! Also interesting, because compared to the other headphones, this one is the lowest priced. Both drivers offer the maximum achievable in terms of transparency and crystal clarity over the entire frequency range. The S is the bass master and the T the version with the golden warm tone. The choice is a matter of taste. Both drivers provide the best sound results in combination with the SRM-009S.

Prices

  • Stax SRM-700T € 4.030,-
  • Stax SRM-700S € 4.030,-

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