How phantom power works. How to use phantom power? External phantom power supply
When building this circuit, it will be useful to add a switch to turn off the battery when the microphone is not in use. The output impedance of this circuit is in the region of 2 kΩ, so it is not recommended to use an overly long microphone cable.
The battery is connected in series with the microphone (Fig.05). This circuit works as long as the DC current from the battery does not adversely affect the preamplifier. In the vast majority of cases, reverse polarity at low voltage will not cause any damage to the microphone capsule.
Note 1: The output of this circuit is a few volts DC. If this creates problems, a capacitor must be added in series with the microphone output. Microphone capsules are not normally susceptible to 3 to 9 volts DC, and will work (although the level of voltage applied may affect the output voltage microphone).
This document contains electrical circuits and information on how electret microphone power is built. Electret microphones are similar to condenser microphones in terms of the conversion principle. mechanical vibrations V electrical signal. The load resistor determines the capsule resistance, and is designed to match the low noise preamplifier. Electret microphones require a bias voltage for the built-in buffer preamp. First of all, you need to make sure that the microphone in the selected tube is electret. Many small camcorders and recorders use a 3.5mm stereo mic plug to connect stereo microphones. Some devices are designed for microphones with an external power supply, while others supply power through the same connector that carries the audio signal.
Popular phantom power good quality and at affordable prices you can buy on AliExpress.
There are still 12 volts, tape ones, as a rule, +60 volts were still ours, Oktava, LOMO and, in my opinion, Screen ... The problem is that the signal from the microphone is not visible on the computer i.e. does not come to it - the level stands still and does not react. Maybe the problem is in the adapter from XLR-3 to minijack, or in the wretchedness of the built-in audio card? It turns out that none of the above cable pinouts will suit you.
That is, we get that the minimum is 32V, but if the sound is cleaner at higher voltage, then more voltage welcome, but within 48V. And how important is which microphone? There is a suspicion that the microphone with the cord that comes with the kit works, as it were, at half strength. Then R7 can be excluded from the circuit. He's not needed. Your phrase is not clear: “with a sound system at ~ 4V it works decently better.” Explain in more detail. Well actually yes. But if R7 is excluded then the XLR pins will be connected to the circuit. The voltage will depend on the value of the resistor and the microphone.
Want to choose a microphone for a recording studio? The quality of these microphones is recognized all over the world! Abroad microphones "Oktava" are as popular as microphones of firms: Rode, AKG, Neumann, Shure ... This is an old, reliable, proven scheme. Such microphones are used mainly in studios when recording, they give a very natural and high-quality sound. They also have great sensitivity. This site presents the product line of the Oktava plant for professional work with sound.
However, with condenser microphones you can achieve greater sensitivity, and a softer, more natural sound, especially on high frequencies. In addition, condenser microphones can be made very small without sacrificing performance. Phantom power supplies have current limiters that prevent damage to the dynamic microphone in the event of a short circuit or incorrect wiring. A microphone whose output is the same for all frequencies has a flat frequency response. Microphones with a flat frequency response usually have an extended range. In addition, we cannot turn the omnidirectional microphone away from unwanted sound sources such as portals, which can cause windup (effect feedback). A balanced microphone input amplifies only the difference between the signals, and ignores the part of the signal that is the same on both conductors.
P.S. It is also possible that the power is being drained due to leakage in the capacitors. The problem of feeding electret "tablets" of the Panasonic WM61 type was solved in the radio business very simply. The value of the resistor R2 can vary from 20k to 120k. If you have golden ears, experiment and select the resistor value by ear according to the best sound within these given limits. It is also worth hearing to pick up the value of the capacitor C1. The value of which will be 0.022 microfarads for speech and 1 microfarads for recording instruments and vocals. The last two circuits where the resistor to ground are called "Power Divider Power Circuits".
A brief retelling of the article boils down to the fact that a computer microphone is an electret capsule. An electret capsule is, from an electrical point of view, field-effect transistor open source. Firstly, there is no resistor in the drain circuit in the capsule, I saw it myself when I took it apart. Here, the left side of the figure is an electret capsule (microphone), the right side is sound card computer. Compared to a microphone without an amplifier, the signal increased by about 10 times (22dB).
Phantom power supplies are often built into mixing consoles, mic preamps, and similar equipment. The receiving antenna and the receiver (TV) are connected by a coaxial cable. The signal from the antenna reaches the receiver at the same time that the low-noise amplifier built into the antenna is powered from the receiver side.
Many who design audio equipment (in particular, preamplifiers) probably needed in some design phantom power supply. In addition to using this block within the structure(for example, a power supply for a mixing console), less often this unit may be required and as a stand-alone design. So, for example, musicians using condenser microphones asked me to make such a unit, and even with the appropriate adapter for connecting the microphone to an active speaker or mixer without a built-in phantom power supply.
In general, the design is nowhere simpler. Yes, you will need good stabilization and good noise filtering, which, in general, linear regulators like the LM317 do a good job. The single most important problem is where to get enough AC voltage(at least 32V)? Transformers over 24V, it seems, are not a shortage, but a very specific thing that is not always at hand.
Here comes help voltage multiplier on capacitors and diodes. The scheme has long been known and very common, almost everyone has heard about it, for sure. And who has not heard - Google to the rescue :)
I will not dwell on the multiplier separately. I will clarify only one feature - a diode multiplier impractical use on high currents loads. But, since standard phantom power consumers are ultra-low-power, this solution is just perfect for them.
Let's stop at a multiplier by 4. Indeed, finding a transformer for 12-15 volts is as easy as shelling pears. There is another reason for choosing a multiplier by 4 - this is the presence of a common point for entry and exit, which is just a minus. And this is also a major advantage. So, multipliers built according to other possible schemes (including with other multipliers) need to be powered from a separate winding or transformer as shown in the figure below. Option I. This is due to the fact that in common circuitry, the negative output of the converter is connected to the zero point of the common power supply (total mass), and combining the input and output of the multiplier at this common point, or, even more so, connecting them through another winding, will lead to its failure ( breakdown of diodes).
This multiplier can be turned on according to the scheme under option II, which means - significantly simplify the design and save on the transformer.
So let's look at the diagram below. It's more than simple. The multiplier mentioned above, a common zero, the LM317 stabilizer, included in the standard scheme. zener diode VD2 is added to protect the chip from maximum allowable voltage drop between input and output (according to the documentation - 35V). Indeed, such a drop can be short-term - at the moment of charging the capacitor C7 or in case of too incorrect installation R5 values (the latter is unlikely). At this moment, the zener diode shunts the microcircuit, thus protecting it from failure. The reverse voltage of the zener diode should be no more than 35V, but at the same time not too small in order to maintain a sufficient range for adjustment and stabilization. Especially for cases when the transformer produces more than 12V. Then you can set the desired value of the output voltage of the stabilizer (48V in our case) using R5. By the way, I would not recommend applying an alternating voltage of more than 20V.
Let's consider it in a little more detail. C1 - C4 and VD1-VD4 in this case form a voltage multiplier by 4. After them, we provided double filtering - to reduce the background.
First comes, in fact, a second-order filter on R1C5 and R2C6, then an active filter / stabilizer on LM317. And after the microcircuit - necessarily - the capacitor C7, which prevents self-excitation of the circuit. In early modifications of the circuit without this capacitor, strong power noise often appeared and disappeared instantly if a capacitor was connected to the output or the load was capacitive in nature.
The trimmer resistor R5 sets the output voltage. Recommendations for setting it up are at the end of the article. R3, R4 and R5 we recommend using powerful ones (0.25W, 0.5W), because in some cases they will get hot.
We also recommend paying attention to VD6. If the circuit is powered by a separate transformer (or a separate winding) - there is no need for it and it can be replaced with a jumper. However, if the circuit is powered from one of the windings of the transformer of a bipolar power supply, or another stabilizer is powered from the same winding, a diode is necessary to protect against a short circuit of the diode in the circuit of another rectifier connected to the same winding when connecting the signal ground. Why this short circuit can occur, which can lead to the failure of the rectifier, and how the diode solves this problem, is shown in the diagram below.
And here is a modified circuit for using the power supply as a stand-alone device. Here is the standard connecting a device that needs phantom power. It is fed through the limiting resistors R6 and R7 to the signal contacts of the device (for standard condenser microphones
with an XLR connector, these are pins 2 and 3, 1 is common), and the signal directly through the coupling capacitors C8 and C9 is fed to the receiving device ( mixer, amplifier, sound card).
Also ready for you - developed and tested printed circuit board. Layout - above, below you will find a link to the file in the format Sprint layout and Gerber if you want to make your own boards. You also can order from us a ready-made factory printed circuit board and even an assembled device . To do this, contact us via the contact form!
Attention! Additional information on this scheme on user questions!
Many who have collected this device according to the multiplier scheme by 4, they complain about the nutritional background.Therefore, I consider it necessary to pay attention to the following: diagram needed adjust the circuit with a trimmer R4 so that the background is minimal, and the voltage at the same time is maximum! Linear stabilizer works as a filter if a voltage drops across it, commensurate with the amplitude of the ripples. I deliberately did not set the exact value of the divider resistors, which select the output voltage in order to be able to adjust the circuit for different transformers (from 10V to 16V). A condenser microphone is not so critical to power to achieve exactly 48V. Therefore, if the transformer you have chosen does not produce enough normal operation voltage circuits, an output voltage of at least 37V will be acceptable.
Happy assembly everyone!
The farther, the more funds appear to improve computer devices, which, for one reason or another, fall short of the required level. In many cases this is not software solution, but independent devices that enhance one or another side of the functioning, for example, a microphone.
What is phantom power for a microphone
In particular, it is about additional food, which is called phantom. Whatever the linguistic constructions, this is a device that will add energy to a suffering device immediately as much as 48 V.
According to the already established tradition, all new and unusual devices are bought on AliExpress and come to the customer by mail. It remains for the latter to understand what is in his hands and why it is needed.
Here is a phantom-type device, and this device is such a purchase. The device feeds a condenser studio microphone, which works much like, in fact, a capacitor. Only instead of the movable lining of the capacitor, the microphone membrane functions. The intensity of work and the amplitude of the displacement determines the strength of the sound that the microphone in this moment processes. Accordingly, the operating voltage changes, and we get the desired effect of improving the performance of the sound recording device.
It should be noted that the scheme is quite original, but working. In any case, the cost of phantom power is not prohibitive, if its capabilities are not satisfactory, the financial costs will not be critical.
Whatever it was, but the new 48 V power supply must be connected somewhere and somehow, and also fastened for safety. Moreover, without it, condenser microphones simply will not function. Why exactly 48 V? Because this indicator is supported by most manufacturers of microphones and sound cards, this is already a certain tradition. In fact, a condenser microphone is capable of operating in wide range voltage.
The device itself, that is, phantom power, should be fixed in a convenient place so that it does not interfere, and at the same time be easily accessible. All necessary cables are connected to the fixed device, including a wire for connecting a microphone. A dedicated button allows you to turn phantom power on and off as needed.
Phantom power - inexpensive and effective method improve the performance of the computer's sound recording system as much as possible. The device is popular with consumers, as it is safe to use. Unless in the event of a short circuit in the cable, especially in the absence of grounding due to such cases, the capsule can be damaged, which is easy to replace.
According to most users, ordering a device from Chinese retailers is worth it. Especially if there is a need to work with high-quality sound without buying expensive professional equipment.
Not being so-called electrets, an external power supply is required. In accordance with various standards, the voltage required to provide a potential difference between the capacitor plates, as well as to power a preamplifier built directly into the microphone body, ranges from +12 to +48 Volts. The microphone electronics determines the voltage required for each individual model, so that the user does not need to think about exactly how many Volts are required for one and how much for another model.
Phantom power got its name because, along with the audio signal passing through the cable from the microphone to the next device in one direction, the cable is completely invisible to the user, i.e. as a phantom, in the other direction, from the equipment capable of providing phantom power, the voltage necessary to power the microphone passes. Almost all modern audio interfaces and recorders have the ability to turn on phantom power. Be it separately for each channel or a group of channels.
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There is only one type of microphone connection known as phantom power. Phantom power specification is given in DIN45596. It was originally standardized to supply 48 volts (P48) through 6.8 kΩ resistors. The value of the denominations is not as critical as their consistency. It should be within 0.4% for good signal quality. Phantom power is now standardized at 24 (P24) and 12 (P12) volts, but is much less common than 48 volts. Systems using lower supply voltages use lower value resistors. Most condenser microphones can handle a wide range of phantom power voltages. Power supply 48 volts (+10%...-20%) is supported by default by all manufacturers of mixing consoles. There is equipment that uses lower voltage phantom power. Most often, this voltage is 15 volts through a 680 ohm resistor (similar, for example, is used in portable sound systems). Some wireless systems may use even lower supply voltages, 5 to 9 volts.
Phantom power is currently the most common method of powering microphones due to its safety when connecting a dynamic or ribbon microphone to an input with phantom power enabled. The only danger is that if the microphone cable is short-circuited, or if an older design (grounded) microphone is used, current will flow through the coil and damage the capsule. This is a good reason to regularly check cables for short circuits, and microphones for the presence of a ground terminal (so as not to accidentally plug it into a live input).
The name "phantom power" comes from the field of telecommunications, where a phantom line is the transmission of a telegraph signal using ground, while speech is transmitted over a balanced pair.
6.1 P48, P24 and P12 phantom power
There is often confusion about the different but actually similar types of phantom power. DIN 45596 specifies that phantom power can be achieved with one of three standard voltages: 12, 24 and 48 volts. Most often, the way the microphone is powered can change depending on the voltage supplied. There is usually no indication that the microphone is receiving power, but 48 volts will work for sure.
Creating a clean and stable voltage of 48 volts is a difficult and expensive task, especially when only 9 volt krona batteries are available. Partly because of this, most modern microphones are capable of handling voltages ranging from 9-54 volts.
6.2 Phantom power for electret microphones
The diagram below (Fig. 19) is the easiest way to connect an electret microphone capsule to the balanced input of a mixing console with 48 volt phantom power.
Please note that this is just the simplest way to "spandor" an electret microphone to the console. This scheme works, but has its drawbacks, such as high sensitivity to phantom power noise, unbalanced connection (prone to noise), and high output impedance (do not use long cables). This circuit can be used to test an electret microphone capsule when connected to a mixing console with a short cable. Also, when using this circuit, transient noise (for example, when phantom power is turned on or off, when connected to a mixing console, as well as disconnected from it) are very high. Another disadvantage of this circuit is that it does not load the phantom power supply circuit symmetrically. This may affect the performance of some mixing consoles, especially older models (in some mixing consoles, the input transformer may short-circuit and burn out, in which case pins 1 and 3 are closed through a 47 ohm resistor).
In practice, this circuit works when used with modern mixing consoles, but it is not recommended for real recording or any other application. It is much better to use a balanced circuit, it is much more complicated, but much better.
6.3 Symmetrical electret microphone connection
The output of this circuit (Fig. 20) is balanced and has an output impedance of 2 kΩ, which makes it possible to use it with a microphone cable up to several meters long.The 10uF capacitances that are connected to the output of the Hot and Cold pins should be high quality film capacitors. Their value can be reduced to 2.2uF if the input impedance of the preamplifier is 10kΩ or more. If for some reason you use electrolytes instead of film capacitors, then you should select capacitors designed for a voltage of more than 50V. In addition, they need to include 100nF film capacitors in parallel. Capacitors connected in parallel with the zener diode should be tantalum, but if desired, 10nF film capacitors can be used with them.
The cable to be connected must be two-core shielded. The screen is soldered to the zener diode and not soldered to the primer. The pinout is standard for an XLR connector.
6.4 Improved connection of an electret microphone to phantom power
This circuit (Fig. 21) provides a lower output impedance than the circuit discussed above (Fig. 20):BC479 can be used as bipolar PNP transistors. Ideally, they should be matched as closely as possible to minimize noise and gain consistency. Keep in mind that the voltage between collector and emitter can be as high as 36V. The 1uF capacitances should be high quality film capacitors. The circuit can be improved by adding 22pF capacitors in parallel with the 100kΩ resistors. To minimize self-noise, the 2.2 kΩ resistors must be carefully selected.
Source: PZM Modifications web page by Christopher Hicks.
6.5 External phantom power supply
This is the diagram (Fig. 22) of an external phantom power supply used with mixing consoles that do not have phantom power:
The +48V power supply is grounded to signal ground (pin 1). +48V voltage can be obtained using a transformer and rectifier, using batteries (5 pieces of 9V each, 45V total, which should be enough), or using a battery-powered DC/DC converter.
There should be two 12V zener diodes between the signal wires and ground, connected back to back, to prevent a 48V pulse through the capacitors to the input of the mixing console. Resistors with a nominal value of 6.8 kΩ should be used with high precision (1%) to reduce noise.
6.6 Getting voltage +48B for phantom power
In mixing consoles, phantom power is usually supplied using a separate transformer or DC/DC converter. An example circuit using a DC/DC converter can be found at http://www.epanorama.net/counter.php?url=http://www.paia.com/phantsch.gif (single mic preamp circuit from PAiA Electronics).If you are using a battery, you may find it helpful to know that many microphones that require phantom power work just fine with voltages below 48V. Try 9V and then increase it until the microphone starts working. It's much easier than using a DC/DC converter. However, it must be remembered that the sound of a microphone powered by a lower voltage can be very different, and this should be taken into account. Five 9V batteries will provide 45V power, which should be enough for any microphone.
If you are using batteries, short them out with a capacitor to limit the sound path from their noise. To do this, you can use 10uF and 0.1uF capacitors in parallel with the batteries. Also, batteries can be used with a 100 ohm resistor and a 100uF 63V capacitor.
6.7 Effect of phantom power on a plug-in dynamic microphone
Connecting a dynamic microphone with a two-wire shielded cable to the input of a mixing console with phantom power turned on will not cause any physical damage. So the most popular mics shouldn't be a problem (if they're properly wired). Modern dynamic microphones with balanced connections are designed so that their moving elements are not affected by the positive potential received from phantom power, and they work perfectly.Many older dynamic microphones have a center tap grounded to the microphone body and cable shield. This may lead to short circuit phantom power to ground and burn the winding. It's easy to check if this is the case in your microphone. Using an ohmmeter, check the contact between the signal pins (2 and 3) and ground (pin 1, or the microphone housing). If the circuit is not open, then do not use this microphone with phantom power.
Do not attempt to connect a microphone with an unbalanced output to the input of a phantom powered mixing console. This may result in equipment damage.
6.8 Effects of phantom power on other audio equipment
Phantom power at 48V is enough high voltage, compared to what conventional audio equipment typically handles. You must be very careful not to turn on phantom power on inputs that are connected to equipment that is not designed for this. Otherwise, it may damage the equipment. This is especially true for consumer-grade equipment connected to the console through a special adapter / converter. For a safe connection, transformer isolation is used between the signal source and the console input.6.9 Connecting professional microphones to computers
Typical computer audio interfaces provide only 5V power. Often this power is called phantom power, but it should be understood that it has nothing to do with professional audio equipment. Professional microphones typically require 48V power, many will work with 12 to 15 volts, but a consumer sound card won't be able to provide that either.Depending on your budget and tech savvy, you can either switch to using household microphones or make your own external phantom power supply. You can use both an external voltage source and a power supply built into the computer. As a rule, each computer block power supply has a +12V output, so it remains only to connect it in the right way.
7. T-powering and A-B powering
T-powering is a new name for what was previously called A-B powering. T-powering (short for Tonaderspeisung, also covered in DIN45595) has been developed for use in portable devices, and is still widely used in sound film equipment. T-powering is mainly used by sound engineers in fixed systems where long microphone cables are required.T-powering typically has 12V applied to the balanced pair through 180 ohm resistors. Due to the potential difference on the microphone capsule, when a dynamic microphone is connected, current will begin to flow through its coil, which will negatively affect the sound, and after some time will damage the microphone. Thus, microphones specially designed for T-powering technology can be connected to this circuit. Dynamic and ribbon mics will be damaged when plugged in, and condenser mics will most likely not work properly.
Microphones using T-powering are, in terms of circuitry, a capacitor, and therefore prevent leakage direct current. The advantage of T-powering technology is that the shield of the microphone cable does not need to be connected at both ends. This feature avoids the appearance of a ground loop.
The diagram for connecting a microphone powered by T-powering technology from an external source to a mixing console with a balanced input is shown in the figure below (Fig. 23):
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| Fig.23 - Scheme of external power supply T-powering |