What Is Phantom Power And How Does It Work With Microphones?
Phantom power is often required for proper microphone function. What is so “phantom” about this powering method, and why is it so popular with microphones? We'll find out in this article!
What is phantom power? Phantom power is a DC voltage (typically +48 V) that provides power to the active components within certain active microphones. This electric power is transmitted through the same balanced audio cables that carry the audio signal. The term “phantom” comes from the fact that there is no obvious power cable.
In this complete and in-depth guide, we'll unravel the mystery of phantom power and explain everything you need to know about phantom power and its role with microphones.
Table Of Contents
- What Is Phantom Power?
- How Does Phantom Power Work?
- Phantom Power Sources
- The Phantom Power Circuit
- What Types Of Microphones Require Phantom Power?
- Phantom Power Standards
- Does Phantom Power Only Work With XLR?
- Is Phantom Power Dangerous?
- History Of Phantom Power And The First Phantom Powered Microphone
- What Is Digital Phantom Power?
- Other Microphone Powering Methods
- Related Questions
What Is Phantom Power?
As mentioned above, phantom power is a method of providing power to microphones. It is provided by microphone preamplifiers, mixing consoles, audio interfaces, and standalone phantom power supplies.
Phantom power travels from the source (at the mic input) to the microphone through the same cable that sends the mic's audio signal from the microphone to the mic input.
There are no dedicated power cables for phantom-powered mics. Rather, the mic is powered via the same cable that carries the audio signal, hence the name “phantom power.”
The standard phantom power is +48 Volts DC and is typically what you'll get from professional phantom power sources. However, phantom power technically ranges from 12-48 volts with various current ratings between 4 and 22 milliamps.
Phantom power voltage travels through balanced audio cables. More specifically, it is applied equally to pin-2 and pin-3 with respect to pin-1 in balanced XLR cables.
If phantom power is engaged, the voltage measurements between pin-2 and pin-1 and pin-3 and pin-1 will read identical levels. No voltage is present between pin-2 and pin-3.
Though +48 V is the standard, other common phantom voltages include:
- +12 V DC
- +15 V DC
- +18 V DC
- +24 V DC
- +48 V DC
Phantom power is used to power the active components of active microphones. Generally speaking, it is used to power the impedance converters and internal preamps of active microphones along with other active circuits. It is also used to polarize the capsules of condenser microphones that require external polarization.
Note that not all active microphones run on phantom power. DC bias and external power supplies are also common, depending on the type of mic. More on this in the other microphone powering methods section.
It's also important to note that modern microphones that do not require phantom power are designed to ignore it if applied.
Back to the Table Of Contents.
How Does Phantom Power Work?
Now that we have a surface-level understanding of phantom power let's look at how it works.
Phantom Power Sources
Phantom power is ultimately produced using electricity from the power mains or batteries that power the phantom power source. Phantom power sources include:
- Standalone phantom power supply units
- Microphone preamplifiers
- Audio interfaces
- Audio mixing consoles
The above-listed sources contain active units that convert mains power or battery power into phantom power for microphones.
As discussed, phantom power is typically a +48 volts direct current. This 48 V DC is designed to pass through balanced audio cables on the audio lines.
With the typical XLR mic cable, phantom power sends +48 volts on pins 2 and 3 (positive and negative audio, respectively) relative to pin 1 (return).
The Rode NT1-A (pictured below) is a phantom-powered condenser microphone with an XLR output:
The Rode NT1-A is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• 12 Best Large-Diaphragm Condenser Microphones Under $500
• Top 12 Best Microphones Under $1,000 for Recording Vocals
• Top 10 Best Microphones Under $500 for Recording Vocals
• Top 20 Best Microphones For Podcasting (All Budgets)
Rode
Rode is featured in My New Microphone's Top 11 Best Microphone Brands You Should Know And Use.
With TRS (tip-ring-sleeve) audio cables, this means phantom power sends +48 volts on the tip and ring (positive and negative audio, respectively) relative to the sleeve (return).
Note that microphones typically receive phantom power through their connected XLR cable. Still, in some routing situations, phantom power may be sent through a patch bay (via TRS cables) before reaching the microphone.
Phantom Power And The Balanced Audio Cable
For simplicity, we'll discuss phantom power through a common (and typical) balanced 3-pin XLR cable. XLR cables are wired as follows:
- Pin 1: Ground/shield wire
- Pin 2: Positive audio signal wire
- Pin 3: Negative audio signal wire
Basically, the audio from the microphone capsule is sent down pins 2 and 3 (relative to pin 1) of the XLR cable. Audio signals are AC, and pin 2 carries a positive polarity mic signal, while pin 3 carries a flipped, negative polarity version of the same signal.
So the audio signals on pins 2 and 3 are completely out-of-phase with each other. At the balanced mic input (preamp, interface, mixer, etc.), a differential amplifier sums the difference between pins 2 and 3. This means that the resulting audio signal is effectively the sum of two in-phase audio signals.
This wiring setup allows for common-mode rejection (CMR). CMR is the cancellation of similar signals on pins 2 and 3.
For example, any noise or electromagnetic interference in the cable will equally affect pins 2 and 3. Similarly, phantom power applies the same 48 volts DC on both pins 2 and 3.
What does this have to do with phantom power? Well, since phantom power is sent through balanced cables, it does not affect the sound of the audio, nor does it add noise to the signal!
For more information on microphones and balanced XLR cables, check out the following My New Microphone articles:
• Why Do Microphones Use XLR Cables?
• Best Microphone Cables
• Top 11 Best XLR Cable Brands In The World
Using Phantom Power To Power Microphones
So we know that phantom power is a DC voltage on the audio wires of a balanced cable (pins 2 and 3 of an XLR). This voltage is supplied by a mic input circuit and travels through the cable to the microphone's output connector for use within the mic.
Whether they require phantom power to function or not, microphones are designed to effectively take what they need and block what they don't need from the supplied phantom power.
For passive microphones, the DC voltage will typically be stopped just inside the mic's body. This blocking can be accomplished with an output transformer, as is the case with passive ribbon microphones. It can also be accomplished with blocking capacitors in the microphone's output circuitry.
Moving-coil dynamic microphones sometimes do not have output transformers. Their capsules, however, will typically not be affected negatively by phantom power.
Microphones that require phantom power to function properly are designed with the appropriate circuitry to send phantom power where it is required. By the same token, the circuitry is designed to block the DC phantom power voltage from entering circuits where it isn't needed or from reaching the components it may damage.
Essentially the mics that need phantom power will accept it, and those that do not will ignore it.
With those microphones that need it, phantom power is used for the following functions:
- Powering the impedance converter
- Powering the active circuit board components
- Polarizing the externally-polarized capsules
Though +48 V DC is the standard voltage for phantom power, not all phantom-powered microphones require the full 48 volts. Some may only require 9 V DC, while others may even require more than the full 48.
Whatever the required voltage is, the microphone will be designed with appropriate circuits to step up or step down the phantom power for proper powering.
Some lower-end and consumer-grade interfaces, consoles, or other power supplies will not supply the full 48 volts in an effort to reduce costs. A lower phantom power voltage may negatively affect the performance of the microphone.
To find out the true voltage output of a phantom power source, check the device's specifications sheet. Alternatively, use a voltmeter to check the voltage across pins 2 and 1 and pins 3 and 1.
Turning Phantom Power On/Off
Nearly all phantom power sources have switches for turning phantom power on and off.
High-end audio equipment P48 sources (mixing consoles, audio interfaces, etc.) often offer individual phantom power switches for each channel. Other sources may have a single switch for all channels or a few switches that control multiple channels each.
Back to the Table Of Contents.
Phantom Power Sources
As mentioned above, phantom power originates from the power main. There are multiple sources that effectively produce phantom power. The 2 main phantom power sources are:
Microphone Preamplifiers
Microphone preamplifiers typically have an included phantom power circuit with an on/off switch. Because nearly all microphones are plugged into mic preamplifiers, including a phantom power circuit in the mic input makes perfect sense.
The XLR mic inputs in microphone preamplifiers generally have phantom power circuits.
These mic preamps can be found in all sorts of audio devices, including:
- Standalone microphone preamps
- Audio mixing consoles
- Audio interfaces.
A great example of an inexpensive audio interface is the Focusrite Scarlett 2i2:
Focusrite
Focusrite is featured in My New Microphone's Top 11 Best Audio Interface Brands In The World.
Remember that not all microphone preamps will supply the full standard +48 V DC. Some low-quality preamps will supply slightly less. Others are even designed specifically to supply a voltage other than +48 V (more on the other phantom power sources later in this article).
To learn more about audio preamps, check out the following My New Microphone articles:
• Best Microphone Audio Interfaces
• Best Microphone Preamplifiers
Standalone Phantom Power Supply Units
There are also standalone phantom power supply units on the market. These units aren't so popular since most mic inputs are built with a phantom power circuit. However, standalone units are required if we want to plug a phantom-powered mic into an input that does not supply the correct phantom power (or any phantom power, for that matter).
There are wall-plug and battery-powered standalone phantom power units on the market.
Neewer has a 1-Channel 48V Phantom Power Supply on the market:
Back to the Table Of Contents.
The Phantom Power Circuit
Analog audio and phantom power can both be thought of as electrical circuits.
Microphone circuits range from very simple (with passive dynamic mics) to incredibly complicated (with some condenser microphones). This is especially true if we do not understand electrical circuit theory.
On that note, let me preface this by stating that I'm not an expert at electrical circuit theory.
An important safety measure with phantom power is only to switch it on once the microphone is connected to the source. This will help prevent electrical shorting and protect the internal circuitry of the microphone in question.
Note that, with the following 2 basic circuits, we'll be drawing the diagrams with the standard +48 volts DC phantom power.
Basic Phantom Power – Condenser Microphone Circuit
Here is a simplified diagram of a phantom power source (and the mic input) to the right supplying phantom power to a condenser microphone capsule on the left:
As we see above, the phantom power supply, when switched on, passes through equal-value resistors. In the case of standard +48 V DC, these resistors are both standardized to be 6.8 kΩ and allow for equal power on pins 2 and 3 along with proper common-mode rejection. These are typically low-noise metal film-type resistors.
As we'll see in the section on phantom power standards, the value of the resistors isn't as important as the fact that they match to give exactly the same voltage on both pins.
The capacitors C1 and C2 block the DC phantom power from getting into the mic input differential amplifier stage.
The +48 V DC appears on pins 5 and 8 of the audio transformer. Power for the microphone preamp is pulled off pin 6.
The ground and the negative supply for the preamp come from pin 1. The audio output of the preamp appears across the primary of the transformer.
Since the power is tapped from the center of the transformer, any audio is cancelled, and the result is pure DC for the preamp.
Basic Phantom Power – Dynamic Microphone Circuit
The idea here is that there is no flow of current to complete a circuit path that sends phantom power to the ground. The dynamic element is isolated from the ground, which means it will not sustain damage from properly applied phantom power.
Alternatively, dynamic mics will have an output transformer that will not pass any DC voltage to the mic element whatsoever. This is true of all ribbon microphones, which have very sensitive diaphragms.
As we'll discuss later, these passive microphones can still sustain damage from phantom power if an electrical short or surge happens.
Back to the Table Of Contents.
What Types Of Microphones Require Phantom Power?
Active microphones require power to function properly. Many of these microphones use phantom power but not all. So what types of microphones require phantom power and which do not?
Mics That Do Not Require Phantom Power
Let's start by looking at the microphones that do not require phantom power:
- Moving-coil dynamic microphones
- Passive ribbon dynamic microphones
- DC-biased electret miniature microphones
- Tube microphones
Moving-Coil Dynamic Microphones
The Shure SM58 is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• Top 11 Best Dynamic Microphones On The Market
• Top 12 Best Microphones Under $150 For Recording Vocals
• Top 10 Best Microphones Under $500 for Recording Vocals
• Top 20 Best Microphones For Podcasting (All Budgets)
Shure
Shure is featured in My New Microphone's Top 11 Best Microphone Brands You Should Know And Use.
Moving-coil dynamic microphones are transducers that work on the principle of electromagnetic induction. Electromagnetic induction is a passive electrical process.
There are also no active electrical components (amplifiers, impedance converters, etc.) in moving-coil dynamic microphones that require phantom power to operate.
To learn more about dynamic mics, check out my article Moving-Coil Dynamic Microphones: The In-Depth Guide.
Passive Ribbon Dynamic Microphones
The Coles 4038 is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• Top 12 Best Vintage Microphones (And Their Best Clones)
• Top 11 Best Microphones For Recording Vocals
Coles Electroacoustics
Coles Electroacoustics is featured in My New Microphone's Top 11 Best Microphone Brands You’ve Likely Never Heard Of.
Passive ribbon microphones also work on the passive principle of electromagnetic induction.
Ribbon mics typically do not have any active components, so they do not require any phantom power.
To learn more about ribbon microphones, check out my article Dynamic Ribbon Microphones: The In-Depth Guide.
DC-Biased Electret Microphones
The Sanken COS-11D is featured in My New Microphone's 7 Best Lavalier/Lapel Microphones (Wired & Wireless).
Like the majority of miniature lavalier microphones, DC-biased electret microphones are certainly active but do not require phantom power.
Rather, these mics work on a DC-bias voltage. These mics are generally designed with unbalanced mic cables and are powered with a DC-biasing voltage (typically 5 volts DC instead of phantom power's 48 volts DC).
Tube Microphones
The original AKG C 12 is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• Top 12 Best Vintage Microphones (And Their Best Clones)
• Top 11 Best Microphones For Recording Vocals
AKG
AKG is featured in My New Microphone's Top 11 Best Microphone Brands You Should Know And Use.
Tube microphones are also active microphones but require more power than phantom power can provide. Tube microphones require external power supply units to power their active components (tubes and capsules) properly.
Mics That Do Require Phantom Power
Microphones that require phantom power include:
- Electret FET condenser microphones
- True (externally-polarized) condenser microphones
- Active ribbon dynamic microphones
Electret FET Condenser Microphones
The Rode NT1-A is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• 12 Best Large-Diaphragm Condenser Microphones Under $500
• Top 12 Best Microphones Under $1,000 for Recording Vocals
• Top 10 Best Microphones Under $500 for Recording Vocals
• Top 20 Best Microphones For Podcasting (All Budgets)
Electret FET microphones include the DC-biased microphones mentioned above. However, many electret mics require phantom power to function properly.
These electret mics are generally studio-type microphones but range from consumer to professional-grade.
Electret condenser microphone capsules are built with electret material in their design and are quasi-permanently charged. The electret (a portamento between electric and magnet) material maintains a permanent charge across the condenser capsule.
Therefore, external power (like phantom power) is not needed to polarize the capsule of electret microphones.
Instead, phantom power is used to properly power the impedance converters (FETs) and, sometimes, the other active electrical components in the electret microphone's circuitry.
True Condenser Microphones
The Neumann U 87 is featured in the following My New Microphone articles:
• 50 Best Microphones Of All Time (With Alternate Versions & Clones)
• Top 12 Best Vintage Microphones (And Their Best Clones)
• Top 11 Best Solid-State/FET Condenser Microphones
• Top 11 Best Microphones For Recording Vocals
Neumann
Neumann is featured in My New Microphone's Top 11 Best Microphone Brands You Should Know And Use.
True FET condenser microphones nearly all require phantom power. For the most part, true condenser microphones are studio-grade microphones, so phantom powering should be readily available in more situations where a true condenser is used.
Like the electret microphone, true condensers require phantom power to properly power their impedance converters (FETs) and other active electrical components.
Unlike electret capsules, true condenser microphone capsules require an external polarizing voltage. This voltage is supplied by phantom power as well.
Active Ribbon Dynamic Microphones
The Royer R-122 is featured in My New Microphone's Top 11 Best Active Ribbon Microphones On The Market.
Royer
Royer is featured in My New Microphone's Top 11 Best Microphone Brands You Should Know And Use.
Active ribbon mics are passive transducers since they still convert sound to audio via electromagnetic induction.
However, the low-level mic signal from the ribbon element is processed and amplified by active components before the audio signal is outputted from the microphone.
These active components (impedance converters, amplifiers, etc.) generally require phantom power to function properly.
Recap On Microphone Types And Phantom Power
To recap, let's look at a table to quickly lay out which mic types need phantom power and which do not:
| Microphone Type | Does It Require Phantom Power? |
|---|---|
| Moving-coil dynamic | No |
| Ribbon dynamic (passive) | No |
| Ribbon dynamic (active-FET) | Yes |
| Ribbon dynamic (active-tube) | No (external power supply) |
| Electret condenser (FET) - small components | No (DC-biasing source) |
| Electret condenser (FET) - large components | Yes |
| True condenser (FET) | Yes |
| True condenser (tube) | No (external power supply) |
| USB | No (USB power) |
| Digital | Yes (digital phantom power) |
Back to the Table Of Contents.
Phantom Power Standards
Phantom power is standardized under the International Electrotechnical Commission Standards Committee (IEC)'s IEC 61938:2018. This document is otherwise known as “Multimedia Systems – Guide To The Recommended Characteristics Of Analogue Interfaces To Achieve Interoperability.”
The IEC 61938 defines 3 different voltage levels for phantom power:
- P12 (12-volt DC)
- P24 (24-volt DC)
- P48 (48-volt DC, which is the professional standard)
Phantom power is a positive voltage applied to both signal conductors of a balanced cable. Both conductors are fed through resistors of equal value:
- 680 Ω for 12 V
- 1.2 kΩ for 24 V
- 6.81 kΩ for 48 V
This symmetry in circuitry is to maintain good common-mode rejection in the mic input circuit's differential amplifier. The matched resistors must be matched within 0.1% of each other.
Two specialized variants of phantom power have been developed for specialized applications:
- P12L (low-power applications)
- SP48 (super-power applications)
Let's look at the specifications of each of the 5 phantom power standards as defined by IEC 61938 (source).
| Phantom Power Standard | Voltage | Current (Max) | Current (Rated) | Matching Resistors |
|---|---|---|---|---|
| P12L (low-power applications) | 12 V +/- 1 V | 8 mA | 4 mA | 3300-ohm feed resistors |
| P12 | 12 V +/- 1 V | 15 mA | 15 mA | 680-ohm feed resistors |
| P24 | 24 V +/- 4 V | 10 mA | 10 mA | 1200-ohm feed resistors |
| P48 (standard) | 48 V +/- 4 V | 10 mA | 7 mA | 6800-ohm feed resistors |
| SP48 (super power applications) | 48 V +/- 4 V | 22 mA | 22 mA | 2200 ohm feed resistors |
It's important to note that lower-quality phantom power supplies may not supply the full standard voltage(s).
Back to the Table Of Contents.
Does Phantom Power Only Work With XLR?
Although the vast majority of phantom power supplies send P48 through balanced XLR connections/cables, P48 does not necessarily require XLR to function properly.
So long as the cable is balanced, it will be able to pass phantom power.
A common example of a balanced non-XLR cable that passes phantom power is the typical TRS cable used in a studio patch bay.
1/4″ TRS “patch” cables are much smaller than XLR cables and easier to patch. Not only do they connect and disconnect more easily, but their size allows for more patching pathways in a smaller patch bay unit.
The TRS connector is analogous to the XLR connector in the following ways:
| Wire/Conductor | XLR connector | TRS connector |
|---|---|---|
| Ground/Shield | Pin 1 | Sleeve |
| Positive Audio | Pin 2 | Tip |
| Negative Audio | Pin 3 | Ring |
An example of a good-quality middle-price-range patch cable is the Seismic Audio SATRX-3-6.
These TRS patch cables do not generally plug directly into a phantom power source or directly into a microphone. Rather, the patch cables are used in routing setups and will pass audio and phantom power from one point to another.
That being said, there is a big reason why phantom power sources utilize XLR rather than TRS. This reason is electrical shorting (or the lack thereof).
XLR cables are designed with 3 pins. The audio pins 2 and 3 are equal lengths, while the ground pin 1 is slightly longer. This means that when an XLR connector is connected, it is grounded before the audio (and phantom power) circuit is completed. Because pins 2 and 3 are equal lengths, they are connected simultaneously, and no shorting occurs.
TRS connections, on the other hand, are designed sequentially.
So when connecting a TRS plug into a TRS jack, the tip of the plug first hits the sleeve, then the ring, then the tip of the jack. The ring of the plug follows, hitting the sleeve before connecting to the ring of the jack. Once the TRS is completely plugged in, the TRS of the jack fully connects to the TRS of the plug.
However, when physically connecting or disconnecting these TRS jacks, we cause electrical shorts (for example, when the tip connects to the ring). These shorts may very well cause improper flow of phantom power, which can harm the microphone.
For this reason, “hot patching” (plugging in and unplugging patch cables) is not advised while phantom power is engaged.
To recap, XLR connections do not short and are much safer than TRS cables when it comes to carrying phantom power.
To learn more about TRS cable jacks and plugs, check out my article What Is The Difference Between A Microphone Plug And Jack?
Speaking of safety, this brings us to our next section.
Back to the Table Of Contents.
Is Phantom Power Dangerous?
Generally speaking, phantom power isn't dangerous. I've never heard of phantom power causing bodily harm to anyone, for example. However, it is possible for phantom power to damage microphones.
It is important to know how phantom power may negatively affect microphones, so we are better equipped to use P48.
For example, some multi-channel mic preamps can only apply phantom power across multiple channels rather than on a per-channel basis. Knowing whether a microphone can handle phantom power or not is essential in these situations.
The situations that could potentially cause phantom power to damage a microphone include:
- Electrical shorting
- Power surges (including brownouts)
- Sending phantom power to an unbalanced microphone
Phantom Power Damage Through Electrical Shorting
Electrical shorting, which was previously mentioned, will momentarily send the phantom power voltage up one audio conductor rather than both. Even an instant of electrical shorting can cause the DC voltage to enter the wrong parts of the microphone and damage the mic.
Phantom Power Damage Through Power Surging
Power surges can overload the phantom power circuit. The spike in electrical current can fry certain wires or components within the circuit.
Power conditioners are always advised in the studio or any other situation where expensive microphones and audio equipment are being used.
Phantom Power Damage To Unbalanced Microphones
Phantom power requires a balanced connection to work properly. If phantom power is forced through an unbalanced cable to an unbalanced microphone, the 48 volts on the audio cable may very well overload the microphone and cause serious damage.
Unbalanced microphone examples include many karaoke microphones and even many of the professional DC-biased lavalier mics on the market.
Will Phantom Power Hurt A Mic That Doesn't Need It?
Most microphones have balanced outputs with the appropriate output circuitry to either accept phantom power or, if the mic doesn't need phantom power, effectively stop it from entering the mic's circuitry.
One such example is the output-coupled transformer which only passes AC voltage (the mic signal). Having a transformer at the output of the microphone will protect it from proper phantom power.
Some dynamic microphones are transformerless but can handle having phantom power enter their passive circuitry.
So most professional-grade microphones that have balanced outputs will not be damaged by proper phantom power.
One common concern with ribbon microphones is the potential for phantom power to destroy the fragile ribbon diaphragm. Passive ribbon microphones, therefore, are designed with output transformers to protect them from DC voltage.
The microphones that would likely get damaged by phantom power, even if applied correctly, are unbalanced. Think belt-pack lavalier microphones and karaoke mics.
Fortunately, these microphones do not have XLR connectors, so it would require some effort (and adapters) to even apply phantom power to the microphones in the first place.
Will Phantom Power Damage Wireless Receivers?
Like professional microphones, the majority of wireless microphone receivers have balanced outputs. These output circuits will typically have the necessary phantom power blockers to keep the receivers safe.
Phantom Power And Battery-Powered Microphones
There are some microphones on the market that offer the option of powering the mic with batteries or phantom power.
It is advised, with these microphones, that we remove the internal batteries when phantom powering is used to avoid the potential corrosion and leakage of the batteries.
In these cases, phantom power may be dangerous in affecting the batteries, though this isn't a major concern.
Back to the Table Of Contents.
History Of Phantom Power And The First Phantom Powered Microphone
Phantom power came about in the 1960s when mic manufacturers began using transistors instead of vacuum tubes in their condenser microphones.
Phantom power came about to power these solid-state mics via the same cable that carries the mic audio rather than with an external power supply (like tube microphones).
For a detailed read on microphone history, check out my article Mic History: Who Invented Each Type Of Microphone And When?
From Tubes To Transistors
The vacuum tube was invented in 1904 by Sir John Ambrose Fleming.
In 1905, Lee De Forest invented the first triode vacuum tube (the basic tube used in microphones). The triode vacuum tube patent was awarded in 1906.
It wasn't until 1928 that the first-ever tube condenser microphone was released to the market. This microphone was the Neumann CMV3 (better known as “the bottle”).
Tube microphones, by their design, require a lot of power to polarize their capsules properly and heat their vacuum tubes. This power is supplied by external power supply units that plug into the wall.
In 1947, Bell Labs made a huge advance in the technological world with its new invention: the transistor.
Transistors could effectively fill the role of vacuum tubes with the added advantages of being smaller in size and requiring less power to function properly.
In typical audio technology fashion, it took some time before the first-ever transistor-based microphone. In 1965, Schoeps produced the CMT20, the world's first solid-state microphone. In 1966, Neumann produced the CMV3, the world's first phantom-powered microphone.
To learn more about tube and FET microphones, check out my article What Are The Differences Between Tube & FET Microphones?
Who Invented Phantom Power?
What we know as “microphone phantom power” today originated in the NRK (Norwegian Broadcasting Corporation). Because of the limited daylight in the winter months in Norway, their studios were equipped with auxiliary lighting, which was fed by a +48 volts DC power supply.
In the 1960s, microphone manufacturers began introducing transistor technology into their microphones. Neumann GmbH, eager to bring their new solid-state microphones to Norway, visited the NRK in 1966.
Neumann's new solid-state microphones required less power than the tube microphones that preceded solid-state mics on the market. There was potential to power these microphones without an external power supply but rather through the same cable that carried the audio signal.
And so it was settled that Neumann would design their microphones to run on the +48 volts DC power supply provided by NRK studios. This DC voltage would run on pins 2 and 3 of a 3-pin XLR connector.
Since then, +48 V DC has become the standard (in DIN 45596) for microphone phantom power.
The First Phantom Powered Microphone
Although Schoeps produced the first solid-state microphone with a transistor in 1965 (the Schoeps CMT 20), it was Neumann that produced the first-ever phantom-powered microphone.
This microphone is none other than the legendary Neumann KM 84.
The KM 84 (now discontinued) was a small-diaphragm pencil condenser microphone with an externally polarized capsule and a cardioid polar pattern.
Phantom power effectively polarized the capsule of the KM 84 and powered its active FET circuitry. This microphone used an output transformer.
The Neumann KM 84 is featured in My New Microphone's Top 12 Best Vintage Microphones (And Their Best Clones) and 50 Best Microphones Of All Time.
Related article: Do Microphones Wear Out? And If So, How?
Back to the Table Of Contents.
What Is Digital Phantom Power?
Before we get into the other microphone powering methods, let's discuss digital phantom power.
The Audio Engineering Society (AES) published a set of standards called the AES 42 that specifies 10 volts DC of phantom power for digital microphones.
Digital mics that comply with the AES 42 standard will run on this 10 V DC phantom power. The current of digital phantom power can be as much as 250 mA.
Digital phantom power is delivered in very much the same way as regular phantom power though the vast majority of analog P48 sources do not supply digital P10. Rather, digital phantom power supplies send their power via XLR or XLD connectors.
XLD is a keyed variant of the XLR cable with the same wiring but a different groove for connection that helps to prevent the interchange of analog and digital devices.
To learn more about digital microphones, check out my article Are Microphones Analog Or Digital Devices? (Mic Output Designs).
Back to the Table Of Contents.
Other Microphone Powering Methods
It's important to know that phantom powering is not the only way to get power to active microphones. In fact, there are many other methods to send power to the microphones that require it.
These powering methods include:
DC-Biasing
Bias is a DC voltage generally between 1.5 – 9 volts that travels on a single audio conductor.
Therefore, DC-Biasing is a popular powering method for miniature unbalanced lavalier microphones and is often supplied by wireless lavalier transmitters.
Because of the low voltages of DC-bias supplies, this powering method is mostly reserved to power the JFETs of miniature electret lav mics. With these microphones, only the impedance converter requires power, and a small DC-bias voltage is enough to power them correctly.
T-Power (A-B Powering)
T-Power (T12) is a Deutsches Institut für Normung (German Institute for Standardization) standard written in DIN 45595.
It was one of the first methods to power condenser microphones through their audio cables. Phantom power, however, has effectively replaced T-power as the standard microphone powering technique.
With T-power, 12 volts DC is applied through 180Ω resistors between the positive audio wire (pin 2) and the negative audio wire (pin 3). These 12 volts of potential difference across pins 2 and 3 could lead to high current across these pins, which would likely cause permanent damage to dynamic and ribbon mics. It's no wonder the safer phantom power method has replaced T-power.
Plug-In-Power
Plug-in-power (PiP) is covered by Japanese standard CP-1203A:2007 and the IEC 61938.
Plug-in-power is used to power consumer-grade electret microphones that connect to consumer audio equipment such as portable recorders and computer sound cards.
It is a low-current source that supplies +5 volts DC. This method sends power through an unbalanced cable, using the sleeve/shield as a return.
PiP works similarly to DC-biasing in the fact that it works on an unbalanced line and is typically used only to power the impedance converters of microphones with low power requirements.
External Power Supply Units
An external power supply unit is likely necessary for microphones that require more power than phantom power can provide. This is true of practically all the tube microphones.
Vacuum tubes essentially provide the same function as FETs. That is, they both act as impedance converters and pseudo-amplifiers for the microphone signal.
A major difference, though, is the amount of power they each require. While microphone transistors can work with phantom power, mic tubes require much more power and, therefore, an external power supply unit capable of supplying this power.
One such example of a microphone with an external power supply is the Rode NTK tube microphone.
The Rode NTK is featured in the following My New Microphone articles:
• Top 12 Best Microphones Under $1,000 for Recording Vocals
• Top 11 Best Tube Condenser Microphones On The Market
Batteries
Some microphones are battery-powered. Oftentimes these mics will have an option to power the microphone directly with one of the above-mentioned techniques.
One such battery-powered microphone is the Beyerdynamic MCE72:
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Related Questions
Can you use a condenser mic without phantom power? Though all condensers are active, many condenser mics are designed to function with powering methods other than phantom power. These powering methods include DC-biasing, external power supplies, T-power, and batteries.
What is the difference between a condenser mic and a dynamic mic? The main difference between condenser and dynamic microphones is the transducer element. Condenser mics have active capsules that work on electrostatic principles, while dynamic mics have passive capsules that work on electromagnetic induction.
To learn more about the differences between condenser and dynamic mics, check out my article Differences Between Dynamic & Condenser Microphones.
Choosing the right microphone(s) for your applications and budget can be a challenging task. For this reason, I've created My New Microphone's Comprehensive Microphone Buyer's Guide. Check it out for help in determining your next microphone purchase.
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