Phantom power is the transmission of information signals and power through the wire at the same time. Basically, remote power is used if it is not possible to connect to a 220 V supply network. Recently, such a system has been increasingly used to power security and telephone equipment. The phantom power supply can also be successfully used to connect a microphone, keyboard or electric guitar.
Depending on the method of supplying the supply voltage, there are two varieties of this system. In the first case, the supply voltage is supplied through a separately laid cable or unused conductors of the main cables. In the second case, it is sent along the backbone cable along with the Ethernet network signal. In this case, additional cable conductors are not used.
The 48V phantom power for the microphone is supplied through the signal wires. Capacitors in this case distinguish between AC and DC circuits. It should be noted that the use of power must be approached with all caution, because in the case of switching the microphone input with an unbalanced signal source, an unexpected power supply may cause damage to the device (for the simple reason that voltage will be applied to it).
Phantom power does not adversely affect balanced sources. If a keyboard or an electric guitar is connected to it, then it is necessary to use switchgears, the task of which is to lower the supply voltage to the mark required by the connected device. It is also recommended to ensure that the source to which phantom power is connected does not power other devices that require more current.
If we consider this phenomenon from a technological point of view, then phantom power is a rather convenient way to save copper, but various unpleasant situations arise all too often in practice. It is necessary to use a high-quality separator filter, otherwise the supply voltage may enter the signal circuits, and interference from switching power circuits may penetrate the receiver input or the signal may attenuate in the power filters.
At first glance, everything may seem quite simple and understandable, but this is by no means the case. The fact is that the task of the filter is not only to separate the constant and variable components. Therefore, it must also be broadband. The filter in a wide frequency band should not distort the shape of the signals. In order for the acceptable length of the link not to decrease significantly, it must not lead to noticeable attenuation.
If we consider the practical use of remote power, it is worth noting that two adapters must be used on the P296 cable. That is, each end of the link must have an adapter. They must have separate power and information inputs. Experiments confirm: if adapters are used for the UTP5 cable, then when all cable cores are used for power transmission, the range of the central power supply will almost double.
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.
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.
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 47Ω 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.
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.
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 kOhm should be used high-precision (1%) to reduce noise.
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.
Many older dynamic microphones have a center tap that is grounded to the microphone body and cable shield. This could short the 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.
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, every computer power supply has a +12V output, so it remains only to connect it in the right way.
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 the flow of 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.
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| Fig.23 - Scheme of external power supply T-powering |
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 sufficient alternating 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 the case of too incorrect setting of the value of R5 (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 instantly disappeared 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 needed 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 a file in Sprint Layout and Gerber format 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!
Needed a phantom power supply to connect a condenser microphone to the camera. Immediately the question is: WHY? Then, that the fotik writes sound much better than the built-in sound card of the computer, and the condenser microphone simply already existed.
Budget external sound cards still almost all require additional phantom power. And those that do not require fall out of my budget. So I decided to try to order such a source. 
When you connect a microphone through it to the camera, there are no problems, everything works clearly, everything is clear, it is recorded. However, the first thing I decided to do was to disassemble this interesting box.
The case is interesting in that you can buy it separately for your electronic needs. Another issue is the price, it is not very cheap. Up to three printed circuit boards can be placed inside such a case. A wonderful thing, if not for the price) 
Inside the phantom power supply is a handkerchief made of budget textolite, and the board itself is also soldered at a very low cost. However, no interference is observed at the output during operation, in any case, such interference that I could measure with my multimeter. The output voltage is +47V instead of +48, I don't think it's that critical. In any case, everything works properly.
By the way, I tried to connect to the GoPro Hero 2 camera, it writes sound very mediocre. In fact, recording sound is not her primary task, and she copes with the primary tasks with a bang.
We see a bunch of electrolytic capacitors from an unknown Chinese manufacturer. In any case, such a manufacturer is not known to me, but at work I come across capacitor manufacturers very often.
Well, the transistor also turned out to be a little soldered, I fixed this matter. 
By the way, about the transistor and why it is not attached to either the radiator or the case. Half an hour gave the handkerchief to work by controlling the temperature of the transistor. So it almost did not heat up in a closed case, the situation will be tougher, but I think its temperature will definitely not even come close to the maximum allowable.
By the way, it is worth noting that the power supply of this device is transformer, 18V, 600mA.
If anyone is too lazy to read, then everything is the same in the video, and in addition, you can evaluate the quality of the recording through this phantom power supply. The recording quality was compared when recording through the power supply and through the built-in microphone of the camera.
I plan to buy +4 Add to favorites Liked the review +10 +13
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 sufficient alternating 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 the case of too incorrect setting of the value of R5 (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 instantly disappeared 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 needed 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 a file in Sprint Layout and Gerber format 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!
