Do Microphones Need Phantom Power To Work Properly?


Phantom power is a clever method of powering your microphones.

Do microphones need phantom power to work? Though phantom power (+48V) is a popular method of powering microphones, most mics do not require it to work properly. Passive mics do not need any powering, and even the majority of active condenser mics (electrets) use small DC bias rather than +48V. That being said, some studio mics do need +48V.

So, in short, some microphones need phantom power and some don’t. Let’s dive into the details of phantom power and its role with microphones.


What Is Phantom Power

Before we too deep into our discussion of microphones and phantom power, it’s important to define what phantom power is.

If you’d like to skip ahead to the list of microphone types that do and do not require phantom power, click here.

So what is phantom power? Phantom power (+48V) is a method of sending DC voltage through a balanced cable in order to power the active components of a microphone. Phantom power sends its 48V DC down both signal wires of a balanced cable and is therefore not introduced in the audio signal.

Though the standard for phantom power is 48 volts DC, some sources provide as low as 12 volts DC and others as high as 52 volts DC.

This DC voltage is used by some active microphones to power their active components, such as:

  • FET (field-effect transistor).
  • Printed circuit board (PCB).
  • Externally-polarized condenser capsules.

You may be asking “what about the vacuum tubes in tube microphones?”

The 48 volts from phantom power is simply not enough to effectively power a tube and so tube microphones will typically have a separate power supply. This power supply will typically be designed to also power the aforementioned active components, meaning that tube mics generally do not require phantom power.

Phantom power can only be sent properly through a balanced cable, which has two signal wires and one ground/shield wire.

Basically, a balanced cable carries balanced audio by having the same audio signal on each of its signal wires. These two signals are equal in amplitude but opposite in phase.

At a balanced input, these two signals are processed through a differential amplifier, where their differences are effectively summed together.

This rids of any common noise introduced on the signal wires (common-mode rejection).

Phantom power has its positive DC voltage sent equally along both signal wires, and so it is also “silent” at the audio input. The input doesn’t hear it, though the microphone is designed to use it (or to nullify it if the mic doesn’t require phantom power).

For more information on balanced audio, check out my article Do Microphones Output Balanced Or Unbalanced Audio?

The phantom power is carried through the same cable as the mic audio and is completely unheard. This is where the term “phantom” comes from!


Passive Microphones

Passive microphones do not require any power, let alone phantom power.

Dynamic microphones (both ribbon and moving-coil) make up the vast majority of passive microphones on the market today.

At their simplest, dynamic mics have their capsules, which convert sound waves to electrical signals via electromagnetic induction, and an output transformer to step-up their signal before the output. Some moving-coil dynamic mics don’t even have an output transformer!

In these microphones, there are no components that require power, and so we can refer to them as “passive microphones.”

So no, passive microphones do not need phantom power to work properly.

For more information on active and passive microphones, check out my similar article Do Microphones Need Power To Function Properly?

This is not to say that all dynamic microphones are passive (though their capsules (cartridges/elements) certainly are. There are active ribbon microphones on the market, which we’ll get to in the next section.

To read more about dynamic mics, check out the following My New Microphone articles:
The Complete Guide To Moving-Coil Dynamic Microphones
The Complete Guide To Ribbon Microphones (With Mic Examples)


Active Microphones

An active microphone contains one or more components that require power in order to function properly.

Here are the 5 common and practical active mic components:

  • FET (field-effect transistor).
  • Printed circuit board (PCB).
  • Analog-to-digital converter (ADC) in USB and other digital mics.
  • Externally-polarized condenser capsules.
  • Vacuum Tubes.

FET

FETs are found in solid-state active mics and act as impedance converters and amplifiers. They can be powered by phantom power.

The FET (field-effect transistor) or JFET (junction-gate field-effect transistor) is a transistor that is put inline directly after a condenser capsule in solid-state (non-tube) condenser mics.

An external voltage causes a base current through the FET/JFET. This electrical signal is the modulated by the output of the condenser capsule.

The output of the condenser capsule is very high impedance, which means that it will not travel well through any cable and that it requires an even higher load impedance (the input impedance of the device that’s next-in-line).

The input of the FET/JFET is high impedance, which makes it perfectly accepting of the capsule’s output signal. The output of the FET/JFET is much lower and can be used effectively with the rest of the mic’s circuitry. It can then be outputted from the mic with the capability of travelling long distances in a balanced cable.

For more information on FETs and JFETs, check out my article What Are FETs & What Is Their Role In Microphone Design?

PCB

Rode NT1 Printed Circuit Board

PCBs often include the FET within them. They provide all the circuitry of an active microphone (this includes any switches, filters, pads, etc.). PCBs can be powered by phantom power.

The PCB (printed circuit board) hosts the inner circuitry of the active microphone. PCBs can be as complex or simple as the mic’s functionality calls for.

ADC

ADCs are found in USB and other digital microphones. These components are powered via the +5 V DC USB bias voltage and are not powered via phantom power.

The ADC (analog-to-digital converter) effectively converts the analog output of a USB mic’s capsule into digital audio information that is then outputted from the microphone.

For more information on USB, analog and digital microphones, check out the following My New Microphone’s articles:
How Do USB Microphones Work And How To Use Them
Are Microphones Analog Or Digital Devices? (Mic Output Designs)

Externally-Polarized Condenser Capsule

Externally-polarized condenser capsules or “true” condenser capsules do require power to function. Solid-state true condensers will generally use phantom power to do this while tube condensers will generally use the power from their dedicated power supply.

AKG CK12 Externally-Polarized
Condenser Mic Capsule

The externally-polarized condenser capsule, like the electret condenser capsule, is the transducer element of the microphone. It converts sound waves into electrical audio signals via electrostatic principles.

Basically this capsule acts as a parallel-plate capacitor with the diaphragm as the front plate. As the distance between the plates changes (the diaphragm moves), there’s a change in capacitance and, therefore, an output signal.

In order for this to happen, though, the capsule must hold a constant charge. This charge is supplied either permanently via electret material; with DC bias (which we’ll touch on soon); an external power supply (which we just mentioned); or phantom power.

For more information on microphone capsules, check out my article What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules).

Vacuum Tube

Vacuum Tubes require more power than phantom power can supply. Tube microphones need dedicated power supplies in order to function.

Electro-Harmonix
6072A/12AY7EH Microphone Vacuum Tube

The vacuum tube acts as an impedance converter and amplifier for the low-level high-impedance signals from condenser capsules.

That being said, tubes have found their way into some modern ribbon mics (such as the Royer R-122V).

Vacuum tubes have largely been replaced by transistors (FETs/JFETs), although their “tube sound” is highly sought after by audiophiles, engineers, and musicians alike.

For more information on microphones and tubes, check out my article What Is A Tube Microphone And How Do Tube Mics Work?


Other Methods Of Powering Microphones

So we’ve touched on a few active mic components that do not work with phantom power. Let’s discuss the other ways that these active mics could receiver the necessary power:

  • DC bias voltage.
  • External power supplies.
  • USB power.

DC Bias Voltage

Bias voltage is a relatively low DC voltage (typically between 1.5 and 9.5 volts DC).

DC bias voltage is not likely strong to power up a solid-state condenser mic’s FET and PCB while also polarizing the capsule. It is certainly not enough to power a vacuum tube.

So DC bias voltage is typically used to power small electret microphones. Electret mics have permanently-polarized capsules and so they only require power to run their transistors and active PCBs.

Now, some electret studio mics (like the Rode NT1-A) require phantom power to function.

Rode NT1-A
Runs On Phantom Power

However smaller lavalier-type electret mics have smaller components are run perfectly well with DC bias voltage.

Sennheiser MKE2
Electret Lavalier Mic
Runs On DC Bias

Rode and Sennheiser are featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.

External Power Supplies

External power supplies are needed for tube microphones since tubes need more power than what phantom can provide.

The power supplies often connect in-line between the mic and the mic preamp. They provide enough power for all the active components within the mic.

Neumann U67 Tube Microphone
With Power Supply

Note that these power supplies require more pins than the typical 3-pin XLR to connect to their mics in order to carry this power.

Neumann featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.

USB Power

USB power is a +5 V DC carried on pin 1 of the USB connector.

USB power is used to power the FETs and ADCs of condenser USB mics (they all have electret capsule). With dynamic USB mics, the USB power is simply used to power the ADC.

Blue Snowball USB Microphone
Runs On USB Power

Blue is also featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.


Which Microphones Need Phantom Power?

To recap, I’ve made a list of microphone types that do and do not require phantom power. For those in the grey area, I provide the designs that would require phantom power and the designs that would not.

Microphone TypeDoes It Require Phantom Power?
Moving-coil dynamicNo
Ribbon dynamic (passive)No
Ribbon dynamic (active-FET)Yes
Ribbon dynamic (active-tube)No (external PS)
Electret condenser (FET)Yes (if components
are large enough)
Electret condenser (FET)No (DC bias if components
are small enough)
True condenser (FET)Yes
True condenser (tube)No (external power supply)
USB No (USB power)

Note that electret mics are the most common in the “grey area” of phantom power. As a general rule of thumb, if the electret mic has an XLR output, it is designed to work with phantom power. If the electret mic is designed with any other type of connector, it isn’t.

Related article: How Do Microphones Work? (The Ultimate Illustrated Guide).


The First Phantom Powered Microphone

The Neumann KM 84 was the first solid-state condenser microphone designed to work with phantom power. It was released to the market in 1966.

Neumann KM 84

Related article: Mic History: Who Invented Each Type Of Microphone And When?


Will phantom power hurt a mic that doesn’t need it? Applying phantom power to a microphone that does not require is safe in the vast majority of cases. That being said, phantom power may damage some vintage ribbon mics or transformerless dynamic mics. Hot patching with phantom power engaged should also be avoided to keep your mics safe.

For more info on phantom power and its effects on ribbon mics, check out my article Will Phantom Power Damage My Ribbon Microphone?

Can you send phantom power through TRS? Although phantom power is typically sent through an XLR cable (on pins 2 and 3 relative to pin 1), it can also be sent through balanced TRS cables (on tip and ring relative to sleeve). This is the usual case when sending phantom power through a patch bay.

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