DIY studio microphone repair

The best microphone is a homemade one, one that is made, or rather altered by hand.

The statement is controversial for many, but not for those who approached this problem seriously and closely.

I myself have been engaged in speech recognition on a computer for a long time, and most of my time I spent on setting up the microphone, as well as on choosing the best combination of a computer sound card and the microphone itself. There are many nuances.

If, of course, this is a business, then it is not so pity to spend money on buying an expensive and high-quality microphone, but if this is a hobby and you think about it for amateur purposes, then throwing out two patches for equipment that will be needed from time to time is a pity.

Sound subsystems in laptops, in most cases, leave much to be desired. Of the models I have touched, I liked the microphones and their work in Sony Vaio (tested on vgn crz), and Asus with Ice Power subsystem.

On them, you can not only indulge in a voice search in Google (there are a lot of extensions for the Chrome browser for this, they are almost all the same, they use the same thing, but I found the extension “Voice Search 2.02” to be the most convenient - a microphone icon appears in all input forms by clicking on which can be said or dictated or rather, for example, a search request as in the picture) but already with speech recognition somehow, but still work.

I didn’t manage to achieve any kind of reciprocity from Siri on Apple, to the extent that it could be “used” for something serious, all the same, “confinement” to the English language affects, and I already know the addresses of the nearest dumplings. In any case, Google remains the leader in speech recognition, voice, it’s a pity there is no way to use it programmatically and in Russian so far.

So the main weak point of microphones is sensitivity, and then of course the price.

Here is an example of how you can get around these two restrictions for very little money, and if there are the details listed below, then for free, get a fairly sensitive homemade microphone. A photo of how to make it yourself, a description of the work and a microphone diagram below.

Made by me homemade microphone possesses high sensitivity and is able to perceive even the ticking of a clock at a distance of several meters. It also allows you to record high quality sound using your computer. The recording quality also depends on the capabilities of the sound card in the system unit. In the design of the microphone unit, the components of the used electronics are used to the maximum.

The electret microphone can be taken from any old radio (in extreme cases, from a mobile phone). I used two microphones (+) at once, which significantly expanded the directional pattern of sound perception. The signal from the microphones, amplified by the low-noise transistor VT1, goes to the operational amplifier DA1 (see. drawing - microphone diagram). The output of the amplifier can be connected to ordinary headphones or fed further to recording and processing devices (stationary computer, laptop, etc.).

The microphone amplifier is powered by the battery of any old mobile phone. The duration of its autonomous operation from the battery is tens of hours. You can use a free USB port on your computer to charge the battery. The amplifier can be left permanently connected to the port, since the charging current is low. I took the cable with the USB connector from the mouse.The connector at the output of the amplifier used 03.5 mm, - as for headphones - from any player, the volume control, too, and the rest of the parts, including the SA1 power switch, are any small-sized ones.

All components should be placed on a small fiberglass board (photo 1 - above). I glued a small piece of foam rubber onto the battery, and put the board on top (photo 2). He pulled all this well with electrical tape and tried on the regulator knob (photo 3). Then, to eliminate pickup and interference, such a "sandwich" was placed in a tin screen, which was soldered to the common wire (photo 4, 5).

The microphones should be secured in a piece of dense, soft material. After that, in a piece of foam rubber (which, for example, is used for washing a car), I cut out a niche and inserted the entire block into it (photo b, 7), and pulled a fabric cover over it (photo 8). You just need to provide slots for the plug, switch and volume control.

The first step is to determine exactly what is wrong with the microphone. The most common is:
- the microphone stopped working;
- decreased sensitivity.

If the microphone is professional (and, as a consequence, expensive) or built into another device (computer, camera, music center), then you should not undertake repairs yourself. Better to see a specialist.

If, nevertheless, you decide to repair it yourself, check that the microphone is connected to the device correctly. If this is a computer, then you need to check for the correct drivers.

If the problem is not resolved, then check the integrity of the wire. If it finds a defect, replace the wire with a new one.

If the microphone still does not work, then disassemble it, check the reliability of all contacts. Perhaps it will be enough to fix or bend something to restore the device's functionality.

If the microphone sensitivity has decreased, this can happen most often for three reasons: a blockage has occurred, moisture has got inside, or there is a break in the incoming wire. The way to eliminate the last cause was discussed in the previous paragraph.

If the microphone is clogged, disassemble it. If this is a built-in microphone, then you need to first disassemble the device itself and remove it. Next, wipe the dirty part of the microphone with cotton wool soaked in alcohol. At the same time, make sure that no cotton particles remain on the wiped surface. Reassemble the microphone carefully in reverse order.

Moisture in a microphone is condensation that forms when the temperature changes, high humidity. To eliminate this malfunction, as in the previous case, release the microphone head and dry in a dry place using an incandescent lamp or hair dryer, without damaging the head. Assemble the microphone.

Carbon microphone designation on diagrams

The first carbon microphone was invented in America in the nineteenth century by the inventor Emil Berliner, to be more precise on March 4, 1877. This microphone is one of the oldest types of microphones. Such microphones were used in telephone handsets, and it did not require an amplifier for operation, and it could be connected directly to high-impedance headphones.

Such a microphone consists of a box with carbon powder and a membrane made of a metal film that vibrates under the influence of sound waves. Until they speak in front of the microphone, the membrane is in a motionless state, but as soon as you say something, it then bends inward, then bends outward. At the same time, it either seals or, on the contrary, weakens the pressure on the coal powder, the resistance of the powder, at the same time, also changes, it either increases or decreases. The current in the microphone connection circuit changes accordingly. The following illustration shows how the carbon microphone works:

Figure - How the carbon microphone works

The carbon microphone has a narrow bandwidth, in other words, it reproduces poorly low and high frequencies and has poor sound quality. Also, the device of the carbon microphone can be seen in the figure below:

Figure - carbon microphone device

Dynamic microphone picture on diagrams

In sound recording equipment, mainly electrodynamic and condenser microphones are used. The first dynamic microphone was invented in 1924 in Germany by scientists E. Gerlach and V. Schottky (the latter is of course familiar to many by diodes). Dynamic microphones offer better performance than carbon microphones. In the following figure, you can see the structure of such a microphone:

Figure - dynamic microphone device

In this microphone, the diaphragm is connected to a moving coil, which is located on the shaft and can move forward or backward. In the photo below you can see an electrodynamic microphone with a 3.5 mm mini jack plug, with a 6.3 mm jack adapter.

Such an adapter is needed in order to connect a microphone with a 3.5 mm mini jack, designed for connection to a computer, to more serious sound recording equipment with a 6.3 mm jack. Also, such connectors are found on music centers and DVD players with karaoke function.

Photo - adapter jack 3.5 -6.3 mm

The principle of operation of this microphone is as follows: When a string sounds in front of the microphone, the membrane begins to vibrate with the coil attached to it, and the coil crosses the magnetic lines of force of the permanent magnet. An alternating audio frequency voltage is induced in the coil. The vibration amplitude depends on the sound volume. The figure below shows the connection diagram for a dynamic microphone:

Dynamic microphone connection diagram

The diagram shows a matching transformer. It allows matching the low impedance of the microphone coil with the high impedance of the audio amplifier. The figure below shows the designation on the microphone diagrams:

Microphone designation on the diagrams

We have already examined carbon and dynamic microphones, and now we will study condenser and piezo microphones.

Condenser microphone picture on diagrams

The condenser microphone was invented in 1916 by Eduard Wente. Such microphones, as the name implies, are made on the basis of a condenser. The device of such a microphone can be seen in the figure below:

Condenser microphone device

One of the capacitor plates is made of a polymer film with metallization, this film, when vibrating with an acoustic frequency, changes the capacitance of the capacitor. These microphones have very high output impedance and require a preamplifier. Photo shows a studio condenser microphone:

Photo condenser microphone

Piezo microphone picture on diagrams

The piezoelectric microphone was invented in the Soviet Union by scientists S.N.Rzhevkin and A.I. Yakovlev in 1925.

The principle of operation of such a microphone is based on the fact that when a piezo crystal is deformed, electric charges arise on its surface. These microphones are used in pickups in acoustic guitars.

Photo piezomicrophone in guitar

An amplifier connected to a piezo microphone must have a high impedance input. Piezoelectric microphones are not used in studio recording, as they cannot provide the high quality required in such cases. In the figure below you can see its structure:

Piezo electric microphone device

Wireless Microphone Photo

Microphones can be connected to the amplifier, either with a cable or wirelessly via a radio channel. The distance at which the average wireless microphone works can be up to 100 meters or more. Such microphones are convenient in everyday life, for use in karaoke during parties. Wireless microphones operate in the VHF and UHF bands.

Wireless Microphone - Kit

Photo directional parabolic microphone

Currently, electret microphones are used almost exclusively (mobile equipment, voice recorders, PC headsets), other types are much more rare. The review was prepared by order of the site Radio circuits ... Author - AKV.

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Is your TV, radio, mobile phone or kettle broken? And you want to create a new topic about this in this forum?

First of all, think about this: imagine that your father / son / brother has an appendicitis pain and you know from the symptoms that it is just appendicitis, but there is no experience of cutting it out, as well as the tool. And you turn on your computer, access the Internet on a medical site with the question: "Help to cut out appendicitis." Do you understand the absurdity of the whole situation? Even if they answer you, it is worth considering factors such as the patient's diabetes, allergies to anesthesia and other medical nuances. I think no one does this in real life and will risk trusting the life of their loved ones with advice from the Internet.

The same is in the repair of radio equipment, although of course these are all the material benefits of modern civilization and in case of unsuccessful repairs, you can always buy a new LCD TV, cell phone, iPAD or computer. And for the repair of such equipment, at least it is necessary to have the appropriate measuring (oscilloscope, multimeter, generator, etc.) and soldering equipment (hair dryer, SMD-hot tweezers, etc.), a schematic diagram, not to mention the necessary knowledge and repair experience.

Let's consider a situation if you are a beginner / advanced radio amateur soldering all sorts of electronic gizmos and having some of the necessary tools. You create an appropriate thread on the repair forum with a short description of “patient symptoms”, ie. for example “Samsung LE40R81B TV does not turn on”. So what? Yes, there can be a lot of reasons for not switching on - from malfunctions in the power system, problems with the processor or flashing firmware in the EEPROM memory.
More advanced users can find the blackened element on the board and attach a photo to the post. However, keep in mind that you are replacing this radio element with the same one - it is not yet a fact that your equipment will work. As a rule, something caused the combustion of this element and it could “pull” a couple of other elements along with it, not to mention the fact that it is quite difficult for a non-professional to find a burned-out m / s. Plus, in modern equipment, SMD radioelements are almost everywhere used; The subsequent restoration of which will be very, very problematic.

The purpose of this post is not any PR of repair shops, but I want to convey to you that sometimes self-repair can be more expensive than taking it to a professional workshop. Although, of course, this is your money and what is better or more risky is up to you.

If you nevertheless decide that you are able to repair the radio equipment on your own, then when creating a post, be sure to indicate the full name of the device, modification, year of manufacture, country of origin and other detailed information. If there is a diagram, then attach it to the post or give a link to the source. Write down how long the symptoms have been manifesting, whether there were surges in the supply voltage network, whether there was a repair before that, what was done, what was checked, voltage measurements, oscillograms, etc. From a photo of a motherboard, as a rule, there is little sense, from a photo of a motherboard taken on a mobile phone there is no sense at all. Telepaths live in other forums.
Before creating a post, be sure to use the search on the forum and on the Internet. Read the relevant topics in the subsections, perhaps your problem is typical and has already been discussed. Be sure to read the article Repair strategy

The format of your post should be as follows:

Topics with the title “Help fix the Sony TV” with the content “broken” and a couple of blurred photos of the unscrewed back cover, taken with the 7th iPhone, at night, with a resolution of 8000x6000 pixels are immediately deleted. The more information you post about the breakdown, the more chances you will get a competent answer. Understand that the forum is a system of gratuitous mutual assistance for solving problems and if you are dismissive of writing your post and do not follow the above tips, then the answers to it will be appropriate, if anyone wants to answer at all. Also keep in mind that no one should answer instantly or during, say, a day, no need to write after 2 hours “That no one can help”, etc. In this case, the topic will be deleted immediately.
You should make every effort to find a breakdown on your own before you get stumped and decide to go to the forum. If you outline the entire process of finding a breakdown in your topic, then the chance of getting help from a highly qualified specialist will be very great.

If you decide to take your broken equipment to the nearest workshop, but do not know where, then perhaps our online cartographic service will help you: workshops on the map (on the left, press all buttons except “Workshops”). You can leave and view user reviews for workshops.

For repairmen and workshops: you can add your services to the map. Find your object on the map from the satellite and click on it with the left mouse button. In the field “Object type:” do not forget to change to “Equipment repair”. Adding is absolutely free! All objects are checked and moderated. A discussion of the service is here.

We repair studio, concert microphones. Any year of release. With any malfunctions. We also perform their tuning and diagnostics.

Microphone repair is our profession.

We give a guarantee for all repaired equipment.

Remember! Any attempt at self-repair can turn for you, at best, an increase in the cost of repairs, and at worst, the impossibility of repairing your equipment.

Microphone - an electroacoustic device that converts sound vibrations into vibrations of an electric current, an input device. Serves as the primary link in the chain of the sound recording path or sound reinforcement. Microphones are used in many devices such as telephones and tape recorders, sound and video recording, radio and television, radio communications, and ultrasonic testing and measurement.

It is assumed that the customer knows the problem of the breakdown and does not require disassembly of the equipment to solve it. And also the customer has all the necessary spare parts in stock. (e.g. replacement of a connector, plug, etc.)

• The duration of the repair is no more than two days
• Diagnostics are not included in the price

A microphone in a mobile device can become unusable due to several factors. The most common is mechanical damage after a fall. Parts of "clamshells" and "sliders" especially often suffer from careless handling. Microphones and speakers of such phones stop working if the loop is damaged.

If there is no service center nearby, the question becomes how to fix the microphone with your own hands. This is easy to do, the main thing is to correctly diagnose the cause of the malfunction. If the matter is in a damaged cable, it is enough to replace the worn-out part.

Often, the microphones of mobile devices stop working due to moisture in them. Self-repair in this case comes down to drying the element and testing it for performance. If the microphone fails to revive, replace it with a new one.

Most modern headsets have capsule-type electret microphones. Inside them there is an amplifier that makes it necessary to strictly observe the polarity of the connection of the element. Headset microphones are sensitive to membrane deformation.It is not recommended to clean the holes in them yourself.

Elements do not withstand high temperatures. If the microphone needs to be replaced, you need to re-solder it with a low-power soldering iron. In this case, it is recommended to act quickly and accurately. The slightest overheating leads to the failure of the element. The best way to solder the microphone is to use an organic contact flux. It optimizes heat dissipation, which will shorten the soldering time.

The operability of the microphone is checked by connecting it to a known working technique. It is not difficult to do this at home. In service centers and workshops, sensitive microphones are tested by various methods, including using elementary circuits of inverting amplifiers with 1-pole power supply.

When self-repairing the headset microphone, it is irrational to disassemble it for restoration. Cheaper, easier, more convenient to replace the damaged element with a new one. Spare parts will not be difficult to purchase at electronics and component stores. If the headset does not work after replacing the microphone, look for the problem in other elements and assemblies of the device.

Repair, pumping and upgrade of studio microphones.
Adjustment of studio microphones to the level of U-67 U-47 C12 C800, etc.
Conversion of microphones U-87 and TLM-67 to U-67
Transferring the tlm-103 and tlm-49 microphones to the tube M49.
Converted Nady 1050 and 1150 into a decent tube microphone.
Limiting AKG sоlidtube to AKG c-12, U-47 or Sony C800g clones.
Finishing AKG P820 Tube to the level of a decent tube microphone or alteration in C12.
Adjustment of various Octaves of type 5000 to a decent level.
Modding microphones Brauner, David Vosk, Soundeluhe, Miktek, etc.
Installation of any kind of capsule at your request.
Repair and maintenance of U-87 and U-87Ai.
Modding the U-87Ai to the level of the vintage U-87.
Finishing the microphone М149Тube (М147) removes overload and plastic, installs vintage transformers and lamps.
Finishing of microphones Audio Teshnis.
New copper cables and block prevention. Fighting noise.
Repair of almost most famous studio microphones.

Call us! Correspondence is NOT welcome!

We have made modding and maintenance of microphone equipment in such leading studios as:
* studio of Grigory Leps, Alexey Bazich and Pavel Dugin, Lev Sound and Emin, studio Visound and Valery Paramonov, studio of Igor Matvienko, QuartaMusis and Valery Kostin, Sergey Trofimov "Trofim", studio of Andrei Sinyaev, studio Blues-Minus Viktor Farafontov, studio Iosifontov Prigozhin and Valeria, Pravda Production studio and Igor Pavlov, K-Resources studio and Stas Kostyushkin (Tea Together), Lizard studio and Dmitry Koldun, Nadezhda Babkina studio, Rоf Resources and Andrey Cherny, Danny Rite Resources, I-Оne, Ryda Records, Alexey Chumakov's studio and Demidoff Production, Menora Resources, Sputnik studio, Valery Demyanov's studio, Igor Loginov's studio, Milk Resorts studio and Sergey Kuptsov, Alexander Kazak's studio, Vinokur's and Alexander Chermyanin's studio, Timur Vedernikov's studio , Evgeny Abramov, Eizer Nazarov, Thomas Evergreen, etc.

* NEVE 1073
We also provide a certain service such as modding and pumping up to the level of the legendary NEVE of all kinds of remakes such as BAE, Purple, Chandler, etc., the installation of vintage transformers Marinair, Siemens, Telefunken.
Modding and prophylaxis of other models of BAE, Рurрlе, Сhandler, Universal Аudio, etc. are also possible.

Repair, pumping and upgrade of studio microphones.
Adjustment of studio microphones to the level of U-67 U-47 C12 C800, etc.
Conversion of microphones U-87 and TLM-67 to U-67
Transferring the tlm-103 and tlm-49 microphones to the tube M49.
Converted Nady 1050 and 1150 into a decent tube microphone.
Limiting AKG sоlidtube to AKG c-12, U-47 or Sony C800g clones.
Finishing AKG P820 Tube to the level of a decent tube microphone or alteration in C12.
Adjustment of various Octaves of type 5000 to a decent level.
Modding microphones Brauner, David Vosk, Soundeluhe, Miktek, etc.
Installation of any kind of capsule at your request.
Repair and maintenance of U-87 and U-87Ai.
Modding the U-87Ai to the level of the vintage U-87.
Finishing the microphone М149Тube (М147) removes overload and plastic, installs vintage transformers and lamps.
Finishing of microphones Audio Teshnis.
New copper cables and block prevention. Fighting noise.
Repair of almost most of the well-known studio microphones.

Call us! Correspondence is NOT welcome!

We have made modding and maintenance of microphone equipment in such leading studios as:
* studio of Grigory Leps, Alexey Bazich and Pavel Dugin, Lev Sound and Emin, studio Visound and Valery Paramonov, studio of Igor Matvienko, QuartaMusis and Valery Kostin, Sergey Trofimov "Trofim", studio of Andrei Sinyaev, studio Blues-Minus Viktor Farafontov, studio Iosifontov Prigozhin and Valeria, Pravda Production studio and Igor Pavlov, K-Resources studio and Stas Kostyushkin (Tea Together), Lizard studio and Dmitry Koldun, Nadezhda Babkina studio, Rоf Resources and Andrey Cherny, Danny Rite Resources, I-Оne, Ryda Records, Alexey Chumakov's studio and Demidoff Production, Menora Resources, Sputnik studio, Valery Demyanov's studio, Igor Loginov's studio, Milk Resorts studio and Sergey Kuptsov, Alexander Kazak's studio, Vinokur's and Alexander Chermyanin's studio, Timur Vedernikov's studio , Evgeny Abramov, Eizer Nazarov, Thomas Evergreen, etc.

* NEVE 1073
We also provide a certain service such as modding and pumping up to the level of the legendary NEVE of all kinds of remakes such as BAE, Purple, Chandler, etc., the installation of vintage transformers Marinair, Siemens, Telefunken.
Modding and prophylaxis of other models of BAE, Рurрlе, Сhandler, Universal Аudio, etc. are also possible.

How to make a stand (stand) for the BM-800 microphone
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Whatever the reason for the malfunctioning of the device, the repair of microphones should be carried out exclusively by professionals who have the necessary skills, technology and parts. These are the specialists who work for Dr. Sound.

Every year the technology market is replenished with more and more new and improved versions of professional sound equipment. As the equipment develops, the range of microphones is also expanding. Modern designs are complex and highly reliable, however, even the latest model can be damaged or disabled.

We will quickly and efficiently repair the following damages:

· Malfunctions in capacitor devices;

· Faults in tape devices;

· The consequences of physical injuries, falls, blows.

The company's laboratory is equipped with high-quality instruments for repairing microphones of various types and brands, as well as equipment for restoring the correct operation of sound, light, studio and musical equipment.

The advantages of cooperation with the masters of Dr. Sound:

1. High-quality service from qualified employees with many years of experience.

2. Flexible pricing policy.

3. The most efficient order processing and problem solving in a short time.

4. Original spare parts and components.

5. Guarantee for all types of services.

6. Free consultation.

Our task is to extend the life of your equipment and ensure stable operation of the equipment for a long time.

Before contacting the service center, you can try to find the cause of the malfunction. If it arose under the influence of external factors, it will be possible to eliminate it on your own. It is quite possible that the problem is not in the damaged structure of the microphone, but in improper operation.

1. The presence of noise, crackling or interference during sound reproduction may indicate that the microphone cable is not working properly. To test this, turn on the system and twist the cord. Is there a crackling sound? So the problem is in a poor-quality cable - it needs to be replaced.

2. Problems in synchronizing the microphone with the computer may occur due to the lack of drivers.Carefully study the installation recommendations that come with your device.

3. One of the most common problems requiring repair of microphones is neglect of timely maintenance of equipment. Try to clean the device, store it in a dry place, and avoid contact with high temperatures or moisture.

A more detailed analysis of the microphone, an independent analysis of the design and attempts to eliminate malfunctions with household items can lead to the death of the equipment. Don't risk it - turn to trusted experts from Dr. Sound!

You can clarify all questions, find out the cost of services and order diagnostics in the office or by calling our managers. The site also presents a wide range of sound, music and studio equipment from global manufacturers.

The experience of repairing foreign models of studio tube microphones and the analysis of circuit diagrams prompted me to create this article.

For a long period of the Cold War, and a couple of decades after, the microphone circuits were mysterious and inaccessible, sometimes you could find out what was inside this or that sound device, you could only disassemble the device itself and draw a diagram of the internal installation, which I did. ... Plus, over time, the hands ended up with “manuals” of those models whose bodies have never come across, and now I am sharing with you my best practices and thoughts on this matter.

Let's start in order, with the simplest, familiar and well-known - the LOMO 19A19 tube microphone. At the end of the 60s, the developers of condenser microphones, finally, had mini-triode tubes in a glass cylinder, which had already ceased to be a strategic raw material, and had very compact dimensions at that time, these were triodes with flexible leads, 6S6B radio tubes. After the 6Zh1P and 6Zh2P used in 19A9 microphones and other early LOMO models, this was a real breakthrough, and someone very clever gave the command to develop a compact tube studio microphone. It is unlikely that we will now be able to interview the chief designer of the microphone, and perhaps he did not exist, because the basis for the shape of the body, apparently, was the dynamic microphones, which at that time were much more compact than studio condensers, and therefore the internal space of the 19A19 body really turned out to be very, very limited. But, surprisingly, Russian craftsmen, specializing, as you know, in horseshoeing fleas, managed to place in this case not only a huge capsule, but also a lamp, and an output transformer, and the entire amplification circuit - that is what interests us.

As you can see, it is as simple as possible, as in textbooks, an amplifier stage based on a tube triode, nothing superfluous, not a single feedback circuit for the amplified signal. By the way, there is almost no gain in this stage, the transmission coefficient of the stage according to the passport is 1.1. In practice, it can differ upward due to the characteristics of the lamps used and the transformation ratio of the output transformer (usually in such circuits it is from 4: 1 to 12: 1).

Neumann, GefelL, Audiotechnica or AKG never used such elementary circuits in microphones - they always wanted to tweak something, introduce some kind of sound-improving feedback, show how educated they are, and generally show off. And only the Russian Vanya did not slyly philosophize, but calculated the cascade according to the textbook for vocational schools, and. thus developed an ingenious thing. But more on that later.

I first noticed the difference in natural sounding between the 19A19 and other expensive tube microphones when such models as AKG C12, Audio-Technica AT 4060, etc. began to be brought to me for repair. The repairs mainly concerned the power supply systems and the switching of microphones; there were no defects that could affect the sound, either in the capsule or in the amplifying part. And that's what interested me.The microphones had a tight bottom, and there were also enough highs, the linearity of the frequency response was evident, but something was wrong, there was some synthetics in them. It was especially strange to notice this in AKG C12 - one of the top tube microphones, accompanied by an impressive case, having a decent weight (in kilograms) and worth fabulous money for Russia, especially at the time of my acquaintance with him (2004). AKG C12 was as if closed from the outside world, it was on its own, and the sound was on its own.
And I turned to the electrical diagram.

However, in the history of tube microphone engineering, there were also interesting examples of the relatively successful use of OOS. First of all, this concerns LOMO 19A9.

The only remark that I would like to make to this circuit is the passage of the audio signal through the cable. Since the signal is transmitted in an unbalanced way, it would seem to be very sensitive to external electromagnetic interference, especially since its level is not high. But the point is that, since it is removed from the anode, it has a constant potential of the order of 50. 60V, and most of the external electromagnetic interference simply cannot overcome the electromagnetic field of the wire itself. BUT! The quality of the sound electrical signal transmitted through the cable from the microphone to the power supply unit strongly depends on the quality and length of this wire. The shorter it is and the thicker the insulation between the wires inside the wire (the less capacity it has), the better. In a long thin or old wire, the HF components will fade, and you may never hear all the charms of the LOMO 19A9 model.

It just so happens that within the framework of this article, we consider the schemes of microphones, not being tied linearly to the time of their appearance, and rather move back, deeper and deeper, to the roots of microphone production. And what happened before that?
And before that there was, for example, a studio microphone Neumann U 47, no less interesting in terms of its circuitry solutions.

In the 40s, Georg Neumann looked at the VF 14 lamp, produced by Telefunken for the electronics industry. Its main feature was that the filament of the VF14 lamp is not high-current, and it can be powered from a high anode voltage, which Georg Neumann did. It was a pentode, which, of course, was switched on in a triode circuit, so that the U47 microphone was switched with just a four-wire wire. Deep AC / DC feedback across R3 gives the amplifier linearity, stability, and minimizes gain distortion. The rest of the circuit is close to LOMO 19A19, except that the Neumann U 47 is a two-membrane microphone and can change the directivity characteristic between the circle and the cardioid. In addition, the Neumann U 47 provides for switching the output resistance, which, apparently, was relevant for the equipment of the 40s.

And finally, I will give you a diagram of the Gefell RFT microphone, apparently, this is CM 7151.

The scheme is almost classic. The decoupling capacitor in the output circuit of the lamp and the sound transformer is connected not with a common minus, but with a common plus (they love this business), plus DC feedback is introduced into the grid bias circuit.

Let me summarize the results of our review.
It is difficult to come up with something new in the schemes of studio tube microphones, each of them is good in its own way, and meets the given characteristics. You need to be careful about the components that make up the electrical circuit of the microphone, especially the capacitors in the old models and to all the details in the new models without exception.
A large number of radio components and switches is not always a plus for studio microphones. In my opinion, if you are chasing naturalness, strive for simplicity. In practice, it often turns out that, like, yes, the old tube microphone does not shine with linear frequency response, but it does not distort the sound and does not embellish it.Tube microphones (especially domestic ones) leave the main thing - the vitality of the material, and then - do whatever you want. If you want - add frequencies that you do not have enough, if you want - cut out the excess, but do it AFTER recording.
The main thing in the microphone is still a capsule, basically we pay this big money for it, and how competently the acoustic environment of the capsule is designed is the know-how of all well-known brands.