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The vacuum tube adds a charm-Stax SRM-700T electrostatic ear amplifier

I wrote Stax again. U-Headphone editor-in-chief Cai Chengrong really wants to frame me. He knows that the editor-in-chief Xiao has been thinking of electrostatic headphones for many years, and every time he pushes Stax into my hands, he simply wants to push the pit. This time I listened to the ear amplifier for SRM-700T electrostatic earphones. Seeing the "T" at the end of the word, you know that it is a vacuum tube amplification. If the end of the word is "S", it means crystal amplification.

The sound show is poisoned as soon as you listen to it

Why are you so interested in Stax? I will never forget the experience of listening to Stax headphones for the first time at the audio show more than 20 years ago. The dummy head recording "The Space Sound CD 1: Dummy Head Recording", the first track is "Kunstkopfumgang Im IRT, Dr "Theile, Sabine, Mike", the speaker was Sabine, who was speaking next to his ear, with a soft acoustic guitar playing in the background, that was Mike, and then Thiele Gunter explained the dummy head recording in German, Sabine translated into English, Gunter Walking and talking in the room, you can clearly hear the sound of speech moving in the space, while the dummy head recording is listened to with Stax electrostatic headphones. The wide sense of space and the real sense of sound movement are definitely the strongest sound of Stax. Features.

However, electrostatic earphones are different from dynamic earphones because of the different sounding principle. The electrostatic diaphragm needs high-voltage drive. Therefore, electrostatic earphones are almost always equipped with special earphone amplifiers. Therefore, Stax is not only an electrostatic earphone, but also a special electrostatic ear amplifier. , You can buy Stax electrostatic earphones separately and pair them with your favorite Stax ear amplifiers, or choose a paired Stax electrostatic earphone system to embrace your own music world.

New flagship series

At present, Stax has a total of seven ear amplifiers. The SRM-700T ranks second only to the flagship SRM-T8000. The silver-white thick aluminum alloy of the chassis panel is similar to the flagship SRM-T8000. The design of the knobs is also similar. You can see the new generation of Stax. The design elements of ear amplifiers will probably gradually follow the flagship SRM-T8000 in the past few years, and change the models step by step from high to low.

SRM-700T feels like an upgraded version of SRM-007T II, ​​but from the price point of view, SRM-700T should be a newly designed new style, and SRM-700S are twin brothers, and the two are like a simplified version of SRM-T8000 Version, and on top of SRM-007T II and SRM 353X, it uses two ear amplifiers to open up a series of new price bands. However, the SRM-T8000 is a front tube and a rear tube, while the SRM-700T is a front tube and a rear tube. It is more like a traditional Stax tube-to-chip hybrid circuit improvement, instead of transplanting the SRM-T8000 circuit. Just look at the vacuum tube model. SRM-T8000 uses 6922, while SRM-700T uses 6SN7.

For SRM-700T front and rear transistors, the first-stage amplification adopts Stax's customized low-noise Dual FET, and the second-stage amplification adopts 6SN7, whichever has the characteristics of high slew rate and clean transparency, which can be seen from here. SRM-700T is not to color the sound with a vacuum tube, but to achieve a highly transparent sound.

Not simple "made-to-order" FET

Regarding the "custom-made low-noise Dual FET", I would like to talk about some content. When I read the data before, I saw these technical specifications and characteristics. I always paid attention to the Dual FET instead of the "custom made". With more contact with the original audio factory, I know how expensive Custom Made is. I want to take a guitar as an example. An introductory model from the American Fender Stratocaster is about one thousand dollars, but the Custom Shop starts at three thousand dollars, and some even sell for seven or eight thousand dollars. The wood is the same and the functions are the same. , Just one "Custom" is several times more expensive, because "customized" must be tailored to the needs of customers. The existing mass production specifications must be modified. The design and production time will be lengthened, and the price will be very high.

Amplifying circuit pursuing low noise

Why does Stax order a Dual FET? The key is "low noise". This is the first stage of SRM-700T amplification. The noise must be low. Otherwise, it will be handed over to the 6SN7 for the second stage of amplification, which will definitely reduce the original noise. Amplify it again, so this Dual FET is very important. Moreover, SRM-700T puts the crystal in the front. I guess the first-stage amplification may have a larger gain, while the 6SN7 may have a small gain, a bit like a buffer stage. The vacuum tube can increase the warmth of the tone, but this is my guess. Stax has not announced the gain technical data of the two-stage amplification.

The reason why Stax needs to be customized is that the noise of the mass-produced Dual FET is not low enough, so I customized it to meet the low noise Stax wants. Moreover, Stax does not make the machine directly after it is customized. Because Dual FETs must be used in pairs, Stax must be measured manually, and the FET with the closest value is used to pair to make SRM-700T. You see, for a small Dual FET, not only do you have to order a certain number of orders, but you also need to measure and pair them one by one. The Hi End audio is really not sold for material money, but time-consuming and labor-intensive hard money. 

Analytical power is emphasized when selecting parts

Next, SRM-700T is equipped with a non-inductive winding resistance. When this kind of resistance is wound, the first turn is forward, and then the reverse direction is wound again. In this way, the positive and negative magnetic fields are offset, and the resistance is non-inductive. Magnetic. Usually use non-inductive winding resistance, the purpose is for more beautiful high-frequency regeneration. As for the capacitor part, SRM-700T also uses supplements. The red WIMA metal film capacitor is selected, which has low error and high resolution.

What else is special about SRM-700T? Looking at the heat dissipation hole of the top cover, you can see the red metal shell behind the volume knob. It is a gold bell iron cloth shirt specially installed for the volume controller to block EMI interference and further reduce environmental noise interference. In the era of widespread wireless networks and 5G broadband, these tiny EMI interferences can be said to be ubiquitous. To pay attention to low noise, it is necessary to isolate these environmental interferences.

The last special feature of SRM-700T is hidden at the bottom, which is the four aluminum alloy feet of SRM-700T. The outer layer is made of aluminum alloy CNC precision car. The special material to block vibration is added in the center, which not only has a good effect of suppressing vibration, but also The material itself has a very high coefficient of friction and can be tightly attached to the surface of the machine. When you plug in and out the earphones, you don’t need to hold the SRM-700T. The soft vibration-damping material of the base will absorb the surface and make the machine Does not slide easily.

The picture on the right is taken from the original Stax website

The function is almost the same as the flagship ear amplifier

The input and output terminals, as well as the method of use, are almost the same as the flagship SRM-T8000, except that the size of the SRM-700T is a bit smaller, the panel does not have a band switch, and the input terminals on the back of the machine are single-ended (RCA) and balanced ( XLR) each set, the switch is placed at the back of the machine, it is regarded as the band switch of SRM-700T.

The volume control of SRM-700T is also comparable to that of the flagship. The left and right channels can be linked, and the volume can be adjusted independently. In addition, there is a Bypass RCA output. If you want to add SRM-700T to the audio system, sometimes you can listen to headphones. When listening to the audio, Bypass is very useful. You can send the signal source to the SRM-700T, and then use Bypass to send the signal to the front stage, and then you can listen to the audio. When you want to listen to the headphones, put the SRM-700T behind Switch to "Internal", and the signal will enter the amplified circuit of SRM-700T without being transmitted to the audio system. With Bypass, it is very convenient for you to switch between headphones and audio.

The tone of Internal and Bypass mode is slightly different

If you connect SRM-700T with DAP or mobile phone, this Bypass function can also be used. When in the "Internal" position, the signal will pass through the amplification circuit and volume control of SRM-700T. At this time, the front-end DAP should try to increase the volume , Use SRM-700T to control the volume, but if you use Bypass, the signal will not go through the SRM-700T's volume control. At this time, the volume control must be adjusted by DAP.

The two ways to listen to the sound will be a bit different. If you use the internal circuit of the SRM-700T for volume control, the sound will be more transparent and detailed, and the sound field will be more open, but if you switch to Bypass, the amplified circuit is equal to full firepower. Not limited by volume control, the sound feels more direct and powerful, but at this time, you need to adjust the volume by the front-end source. When the digital volume is attenuated, the resolution will be lower by a few bits. These two methods to connect SRM-700T, the sound is very beautiful, but there are subtle differences. When I listen to classical music, I will probably use the internal mode, but if I listen to rock music or jazz, I will switch to the Bypass mode. Digital source to control the volume, it sounds more straightforward and refreshing.

It's really nice to match the flagship SR-009S

When I listened to SRM-700T, the headset sent by the agent Shengqi was the flagship SR-009S, which was really unstoppable. Editor-in-Chief Cai was really determined to push it. Although SRM-700T is a vacuum tube machine, it sounds good when it is turned on. Of course, all vacuum tube machines need to be warmed up, and SRM-700T is no exception. The warmer the machine, the better the low-frequency strength and Q elasticity. How long does it take to warm up? After turning on the SRM-700T for a few minutes, the two small dots on the top cover of the case will heat up first, because they are closest to the 6SN7 vacuum tube, and then the heat will slowly spread. After about two or three hours of operation, the whole machine It has a slight temperature to the touch, and the state is best at this time.

Do you have to wait so long every time? The vacuum tube machine is always on, will the tube be easily aging? In fact, there is no need to wait, the SRM-700T sounds good when it is turned on, but when the machine heats up, it works best. As for the aging of the vacuum tube, the SRM-700T uses the GT tube from GE in the United States. It is not only easy to buy, but also inexpensive. The durability is at least 10,000 hours. If you listen for 8 hours a day, you can listen for at least 1,250 days. You only need it for three and a half years. Replace the vacuum tube, not to mention that this is calculated by listening for 8 hours a day. If you only listen for one or two hours a day, the 6SN7 tube may last more than ten years. Please rest assured to use it. The vacuum tube is very durable.

Please try the difference in tone between the two modes

When listening to SRM-700T this time, the biggest new discovery is the difference between Internal and Bypass modes. When listening to the flagship SRM-T8000 before, I did not notice the difference between these two modes. If you have the opportunity to listen to SRM-700T, please remember the two Try all these modes, especially those who like rock music, they will definitely like Bypass mode.

I want to take the "Prodigal Son Turning Head" of Eggplant Egg as an example. The lead singer and keyboardist A Bin said sadly, "Cigarettes one by one, wine cups and cups dry." The keyboard's simple chords respond and the vocals It was very close, as if the murmur of a monologue in the middle of the night, the singing and the piano stopped, the jazz drum made a backhand and brought the orchestra out, and the lively electric guitar Solo sang the scene together with the electric bass and drums. If you use the Internal mode, the concert will be more detailed and gentler, but switch to the Bypass mode, the volume will not change, the strength and thickness of the low frequency band are better than the Internal mode, and it sounds more direct.

The eggplant egg sang vicissitudes of life and helplessness. After all, the end of the song is "One day we will be old, take a certain son for a while, and the prodigal son will turn around." When listening in Bypass mode, rock music is more rough and simple, and the low frequency band is more vigorous. , The voice is more emotional, of course, if you switch to the Internal mode, the sound will be more detailed at the same volume, but if you want to listen to the vicissitudes of the eggplant egg, the voice is a bit thicker and fuller, which is more right.

Bypass mode is so refreshing to listen to rock and roll

Then listen to the eggplant egg, listen to "Just like your tenderness", an old song that the middle-aged uncle loved and sang when he was young. The eggplant egg was sung from the perspective of a young man. At the beginning, the acoustic guitar was well woven and played well. When I use SRM-700T to listen, the space effect created by the recording studio is not missed at all, and I am equipped with the flagship SR-009S. The sense of space, music details and texture are all top-notch, I Can’t help but wonder, will this SRM-700T really lose to SRM-T8000? I heard that SRM-T8000 is also equipped with SR-009S before, and thought it was great, but now I use SRM-700T to listen to it, I think it’s not inferior at all!

After singing "Tenderness Just Like You", the young rock soul of Eggplant Egg is here. Although the Solo of the electric guitar is still an old melody, the tone is already very blue. The vocalist A Bin began to sing his own version, using Bypass mode. To listen to it is equivalent to letting the SRM-700T's amplifier circuit fully fire up, relying on the signal source to adjust the volume, and the low frequency band is more powerful.

Who said that electrostatic headphones do not have low frequency, and paired ear amplifiers know that they are powerful! The music level made by multi-track recording can be heard clearly on the SRM-700T and SR-009S. The sound of the electric guitar Solo is thick and numb. I can’t help but guess that this is probably the Gibson Les Paul from the concert. Is it recorded? The sound is really full and thick!

Fully show the sense of space of the dummy head recording

Shengqi not only sent SRM-700T and SR-009S, but also sent a total of five Stax dummy head recording CDs, which have been collected for many years. It is great, I only have one, and I have not heard of the others, hurry up... ...You know what I'm going to do... Hush, don't tell anyone.

Dummy head recording is a special method for earphone recording. It is to install a microphone in the dummy head to receive the sound. With the shape of the dummy head's auricle, it naturally adds a sense of space during recording and compensates for the lack of ears when listening at close range. The time phase parameter of the sound reflected by the profile. This kind of CD is not suitable for playing on general speakers, and it sounds weird. However, using high-quality headphones to listen to dummy head recordings will have a particularly good sense of space, because this is a recording method specifically designed for headphone replay. Suitable for listening with headphones.

Listening to the dummy head recording of "The Warsaw Baroque Soloists Concerto Avenna", the track is "Concerto Grosso Op.6" by Corey. Listening in Bypass mode, the space feels a bit smaller, the instruments are closer, and the internal mode is more spatial. Better, the sound is more detailed, so when listening to classical music, I will use the Internal mode, and the sound is more refined. The entire concerto consists of eight pieces of music, interlaced in speed and slow. The SRM-700T and SR-009S open up a wide and natural sound field, which is like a large speaker worn on the ear. The dummy head recording enhances this sense of space, although Wearing headphones, but there is the illusion of listening to the sound.

Listening to static headphones requires a quiet environment

To enjoy the beauty of the sound of SRM-700T and SR-009S, just like listening to audio, you need a quiet environment, because electrostatic headphones have almost no sound insulation effect, and the ultra-thin diaphragm is very light and vibrates freely at any time. When I am writing and listening to music, the sound of typing on the keyboard will be transmitted to my ears, detracting from the rich musical details of SRM-700T and SR-009S. However, as long as the environment is quiet enough, SRM-700T and SR-009S will create a high level. The immersive musicality is as transparent as if you are in the recording scene, and the SRM-700T with vacuum tube feels a bit more warm tones, adding a bit of charm to the tone, which is really charming.

Dummy head recording is certainly a plus for reproducing the sense of space, but if you use SRM-700T and SR-009S to listen to any recording, the sense of space will be more open and transparent than ordinary dynamic headphones. I would like to cite Mutter, Yo-Yo Ma, For example, in the "Beethoven: Triple Concerto" by Barenboyne and Berlin Philharmonic, listen to the third movement of the Allegro, the cello leads the theme, but when it is held in the high position, it sounds a bit like a violin, and then the violin continues. , The more you play in the low position, so that the violin is not so bright, this is Beethoven's deliberate arrangement, to confuse people.

Don't be afraid of fucking loudly, but also have appropriate details in a low voice

But take SRM-700T and SR-009S to listen, you will not mistake the instrument, because the timbre and overtones of the instrument, the cello is a bit more generous, the violin is still brighter, and the pleasant rhyme movement, violin, cello and The piano alternately plays the leading role, responding to each other, and decorating each other. There are many dazzling passages interspersed with each other, as if three soloists are going to compete on the same stage. Use SRM-700T and SR-009S to listen. The sound of each instrument is very good. It is accurate and has a good sense of hierarchy. The solo instruments are closer, the orchestra scene is wider, and the distance is a little farther.

In addition, when the SRM-700T and SR-009S are matched, the working linearity is very good, which means that when the volume is low, the sound will not be particularly reduced, and there are still good music details and levels. When the volume is turned on, the audio and video will be As it increases, the tone is brighter, and the mid and low frequencies are fuller. SRM-700T is not afraid of your violent driving. Pushing SR-009S is calm and comfortable, and will not break loudly. I am afraid that listening too loudly will hurt your hearing, but more importantly, listening in a low voice is also good. It can maintain proper music details and levels, and can listen for a long time without getting tired.

Put in the study to enjoy the true happiness

What to do? I was poisoned by Stax again. When the agent asked when I could get it back, I just left SRM-700T and SR-009S for one more week. The more I listened, the more I liked it, the more I listened, the more reluctant to return it. There are too many things I want to buy, but the most important thing is that my desk has no space for an extra SRM-700T, so I have to give full play to SRM-700T and SR-009S, but if you have a place at home SRM-700T can be placed, and there is also a quiet space to listen to music (such as a separate study room), so putting a set of SRM-700T and SR-009S on the desk is definitely the supreme personal music feast.


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