Good day, Datagorians! This project was created due to a passionate desire to listen to electrostatic sound emitters. I have repeatedly read intriguing and enthusiastic reviews: accurate transmission, smooth frequency response, three-dimensional stage, etc., etc. Needless to say, I became interested in electrostats. It turned out that for electrostatic headphones to work, a special high-voltage amplifier is also required to create a polarization voltage. from the industry leader, Stax
, for a modest amount of 80 to 300 thousand rubles. Reading about Stax, I realized that I’m somehow not ready to support this manufacturer right now. So I spent some time searching and studying materials on the topic, and then several evenings putting it together.
Next - details about the manufacture of a set of electrostatic headphones and a high-voltage amplifier.
↑ Let's get to the headphones
We buy simple, cheap headphones like Philips SHP2000.
In the future, they will become the donors of the buildings. Philips SHP2000 headphones
You need to perform the following operations:
1. Disassemble the headphones (be careful not to damage the case, because that is why we purchased them).
2. Dismantle the dynamic emitters. Remove them carefully. Externally, the emitters look good and, perhaps, you will use them in some other design. The parts should be without mechanical damage, as in the photo below.
3. We prepare the following blanks from double-sided foil fiberglass laminate with a thickness of 1.5 mm and a diameter of 77 mm:
4. Insulators must be made from blanks in accordance with this drawing:
I draw your attention: there should be four insulators, two according to Figure 1 and two according to Figure 2. The cutout in the insulator is intended for soldering current-carrying conductors to the inner layer of foil.
5. When the insulators are ready, we proceed to the film (membrane).
Characteristics
- Model: STAX SR-L700 headphones
- Type: Electrostatic/Open
- Electrical capacitance: 110 pF (including cable)
- Bias voltage: 580V (DC)
- Frequency Range (Hz): 7-41k
- Sensitivity (dB): 101 (100 V rms, 1 kHz)
- Impedance (ohms): 145k (10 kHz)
- Design
- Headband: Metal/Plastic/Artificial Leather
- Cups: Plastic
- Ear pads: Over-ear/Genuine lambskin
- Cable: 2.5 m
- Weight: 360 g (496 g with cable)
↑ Assembly of insulators
We do this sequentially:
1. We purchase a Chinese stainless steel sieve. The sieve should be large enough to produce 4 circles with a diameter of 63 mm. First, we disassemble the sieve and straighten it, removing dents. The sieve must be level!
2. Tin the sieve along the edge, as shown in the drawing below. The width of the tinning zone is 0.5...1.5 mm. Here you cannot do without the use of orthophosphoric acid. After tinning the sieve, it must be washed to remove flux residues. I used it at a company. According to recommendations on the Internet, you can use a mixture of equal proportions of alcohol and Galosha gasoline. I haven't tried it personally, so I can't say anything.
3. Now we solder our sieve onto insulators using rosin, according to the drawing below. After soldering, rosin is quite easy to wash off with alcohol. Before soldering incorrectly, look at the drawing of the assembled product and only then proceed to soldering. Photos of finished insulators with a soldered sieve are below. Since I did it the first time, the photo shows a wire soldered to the inner foil of the insulator.
4. Now prepare epoxy resin no more than 3 g. (no longer needed) add graphite powder to it, about 0.5-1 g per 3 g of resin.
5. Apply excess glue to the insulators (2 pieces for different channels) along a radius of 31.5 mm (approximately), excluding excess glue from getting into the through holes and inside the emitter, onto the membrane that has already dried by that time. You can fold insulators on both sides of the membrane and tighten the insulators together with screws through the holes. But it is better to leave the insulators until the resin hardens.
6. The next day or earlier, if the resin has hardened sufficiently, insulators can be glued to the second side according to the drawing below:
The drawing shows a bottom view of the recesses in the insulators. Pay attention before you stick! If it is clear that the membrane is sagging somewhat, it can be tightened by blowing hot air on it from a hair dryer (preferably controlling the temperature of the outlet air with a thermocouple). By uniformly heating the membrane, we achieve uniform tension without bunching (!).
↑ Final assembly
Solder the wires according to the drawing below.
We mount the emitters in the headphone housings according to the figure.
We cut a hole in the headphone body to the size of the emitter and mount it using hot-melt adhesive. When cutting a hole, use the photo as a guide. Unfortunately, I don't have any photographs of the intermediate process. Nuance!
To prevent shorting of conductors with self-tapping screws through the mounting hole, we put insulating tubes on the self-tapping screws.
Next, we solder the wires (I soldered MGTF). We put heat shrink on the wires and shrink them. At the end of the wire we solder it to any convenient connectors that can withstand a voltage of 600-1000V (I soldered it to XLR connectors). At my polarizing voltage of 800...900V, the XLR connectors do not break through. Well, we can assume that the headphones are ready.
A Brief History of Electrostats
The history of electrostats began in the early 20s of the last century. Since the implementation of the technology initially encountered many difficulties, including electrical breakdown, low sensitivity, and the lack of a suitable material for the membrane, the idea was almost forgotten with the appearance on the scene in the 1930s of the voice coil loudspeaker (patented in 1924 by C. Rice and E. Kellogg ).
The situation improved with the invention of Mylar in the 1950s (DuPont patent). At this time, Peter Walker's outstanding QUAD ESL-57 model appeared (see illustration below); The most important milestone in the development of electrostats and audio in general is another Walker model: QUAD ESL-63 (1981). The ES converter is a full-range speaker system, so it usually does not need a crossover, which is a great advantage, since in this case there is no problem of phase distortion.
The most important advantage of ESAS is its excellent transient response. Electrostats are inferior to speakers with speakers in terms of sound pressure level, sensitivity, size and price. Along with the classic ones, hybrid electrostats are currently being produced, in which low frequencies are reproduced electrodynamically (Martin Logan).
↑ Now it's up to the high-voltage amplifier
It was planned that the amplifier would look like this:
But what happened, see below, is somewhat different. I studied materials on electrostats on the sites audiodesignguide.com and dddac.de. There was another resource where I took this diagram as a basis:
But, unfortunately, the resource is not available at the moment and I cannot provide a link.
The circuit diagram of my high voltage amplifier is shown below.
Fragment excluded. The full version is available to patrons and full members of the community.
I don’t give the structure of the voltage multiplier by 2 or 4. I think everyone can find his diagram on the Internet if they want.
Available elements are used in the diagram. Field-effect transistors KP103L instead of J271, instead of KSA1156 I used our KT9115, instead of a 6S4 lamp I used 6N23P (the reason is simple - the high permissible voltage at the anode when the lamp is closed). I didn’t assemble the output stage - I really wanted to hear and appreciate the sound of the electrostats. Yes, I almost forgot: instead of bipolar transistors, I used field-effect transistors KP902B (they were available + they have greater linearity, even if they work in a current mirror). The printed circuit board was not developed, everything was assembled on a breadboard.
Using resistors in the sources of KP103L we set the output voltage relative to the common wire (preferably zero volts). The voltage range is 0…20V, which does not affect the sound quality. If the elements are in working order, the circuit will work immediately. We feed sound to the input and you can listen. The amplitude of the maximum output voltage between the outputs and stators “+” and “-” should be within 120V.
Disadvantages of the current scheme:
— Headphones with a gap of 1.5 mm with this amplitude do not play loud enough. These headphones require a signal amplitude between the stators of at least 250...300V. — In this circuit, it is not possible to obtain an amplitude of more than 120V due to the current cutoff of the input transistors (KP103L) at an input signal amplitude of 0.7-1V (less than 0.7V cutoff is not observed and the sound is clear).
Stax SR-303 - the most affordable This model is designed for beginner musicians and sound engineers. The cost of the most affordable Stax SR-303 headphones in specialized online stores exceeds 21 thousand rubles. This sample is made from the same materials as more expensive models, raising the level of the budget earpeaker line. The ear pads of the headphones are made of high-quality artificial leather with a pleasant texture. Pros of the model The weight of the headphones does not exceed 472 g, which, combined with the optimal design of the headband, does not tire the user. A standard PC-OCC cable has a low capacitance of no more than 120pF, which significantly reduces the level of distortion of the transmitted signal. The maximum sound pressure level of 100 dB provides a wide range of volume adjustments. Disadvantages of the model Some asymmetry in the amplitude-frequency characteristics of the right and left speakers, noticeable by ear. Headphones are extremely sensitive to temperature conditions of use; in hot weather, unpleasant sensations occur in places of contact with the skin. The sample is not very suitable for listening to music and movie soundtracks in a lying position. The Stax SR-303 delivers exceptionally realistic sounds of natural and man-made sounds, from the rustling of leaves to the roar of jet engines. Recommended for use with home theaters and Hi-Fi audio equipment. Stax SRS-005 – the best in-ear headphones Do you love listening to good music while walking through parks and squares? Then you should take a closer look at the Stax SR-305 in-ear headphones, which weigh only 28 g along with a comfortable headband. This scheme ensures reliable fixation of the speakers in a given position, which allows you to achieve high sound frequencies. The moderately elastic arm prevents the slightest movement of the device when a person moves. Advantages of the model Extremely low harmonic distortion of only about 0.1% for devices of this class allows minimizing sound distortion. The possibility of two-way connection of a cable, the length of which is 1.5 m, is a convenient option for a mobile model. The compact amplifier supplied with the headphones allows you to fully enjoy your music on the go. Disadvantages of the model The somewhat narrowed range of reproduced frequencies from 20 to 20,000 Hz limits the scope of application to the entertainment road version. Extreme sensitivity to the quality of the reproduced content, the slightest flaws in the recording are magnified many times over and spoil the impression. The Stax SR-305 headphones are an excellent option for those who like to travel, they provide sound levels close to studio quality. Stax SR-307 - full-size open-back headphones You want to achieve maximum naturalness when listening to music and at the same time remain in reality. The Stax SR-307 open-back over-ear headphones provide the highest sound quality without compromising your ability to communicate with others. Pros of the model The ear pads of the headphones are made of high-quality synthetic leather, which absorbs sweat well and creates discomfort during prolonged use. Speakers right and left are marked with special symbols, allowing you to use saved amplifier settings. The model is equipped with a standard cable with 6 insulated conductors made of oxygen-free honey, which reduces their mutual influence on each other. Disadvantages of the model In the lower bass range, slight sound distortion is possible due to the properties of the diaphragm material. The cable is too short for use in home theater equipment, and the use of extension cords degrades performance. The model has only one driver, which limits its ability to reduce interference in the high and low frequency parts of the range. Stax SR-307 headphones belong to the semi-professional category, they are intended for music lovers and true connoisseurs of cinema. To ensure the proper level of playback, you need equipment of the appropriate class and high-quality content. Stax SR-007 Mk2 - closed-back headphones with excellent sound Strive to achieve complete detachment from reality and immersion in the magical world of music. The Stax SR-007 Mk2 closed-back headphones can perform a real miracle and provide complete sound isolation and excellent sound quality. The frequency range of the speakers from 6 Hz to 41 kHz goes beyond the limits of human perception, which allows you to best convey the slightest nuances of musical works. Advantages of the model The ear pad housings rotate freely relative to the speakers and allow them to be installed in a position that most closely matches the anatomy of the auricle. The design of the headphones eliminates the possibility of any vibrations or extraneous sounds during use. Specially tanned genuine leather provides maximum comfort even with prolonged use. Disadvantages of the model Electrostatic type headphones, due to their design features, are unable to provide decent sound in the low-frequency range. Extremely high demands on the quality of recordings, intolerant of the slightest distortion of the content. Model Stax SR-007 Mk2 – headphones for musicians, composers and recording studio employees. For correct operation, you need appropriate sound-reproducing and amplifying components and high-quality content. Set of Stax SR-L300 headphones and Stax SRM-252S amplifier – top-class equipment Do you want to achieve a high level of sound from your musical works? It is recommended to take a close look at the set of Stax SR-L300 headphones and a Stax SRM-252S amplifier with an external power adapter. The use of such a circuit reliably protects the device from interference and interference from electrical networks. Pros of the model The amplifier housing is made of copper, which ensures good heat dissipation and normal temperature conditions for high-voltage transistors. The headphones do not have latches, which are provided on top models, but this does not create the slightest inconvenience during use. The speakers reproduce sound perfectly in a wide frequency range, harmonic distortion does not exceed 0.01% /1 kHz/ Disadvantages of the model
To avoid possible overheating, the amplifier module should not be kept in clothing pockets. The cylindrical volume control knob without knurls is not very comfortable to use, which makes adjustments somewhat difficult. A set of Stax SR-L300 headphones and a high-quality Stax SRM-252S amplifier allows you to achieve an optimal level of playback with a relatively small investment. Stax SR-009 - the most expensive sample You are not ready for the slightest compromise, are not constrained by funds and want to get the maximum result. The Stax SR-009 over-ear headphones are specially designed for creative people, where every little detail is taken into account and designed to provide inspiration. When creating this model, innovative materials of the highest quality were used. Advantages of the model The patented MLER technology, developed by the company’s specialists for the production of flat electrodes, ensures uniform oscillations of the diaphragm. The speaker housings are made of a special grade of aluminum, which eliminates the possibility of resonance. The connecting cable is made of copper wire with a minimum impurity content of no more than 0.0001% and is silver-plated to reduce parasitic vibrations. Disadvantages of the model
The need to use a special, preferably branded, amplifier. The slightest flaws in recordings are unacceptable; they disrupt the harmony of the sound and spoil the impression. Unjustifiably inflated price compared to other countries, in particular the USA. Stax SR-009 headphones are the best in the manufacturer’s model range and are designed for use by true music connoisseurs with absolute pitch.
