How Are Microphones Powered? (7 Mic Powering Methods)


Many of the world’s microphones require power in order to function. With the various microphone types and countless individual microphone models, we’d expect that there are multiple methods of powering these microphones.

The various microphone powering methods are:

  • External power supply units.
  • Phantom power.
  • DC biasing.
  • T-power (A-B power).
  • Plug-in power.
  • USB-power.
  • Batteries.

In this article, we’ll go deep into each of these microphone powering methods and discuss the various active components within microphones that require these powering methods to function properly.


How Are Microphones Powered?

Active microphones that require power can be powered by many different methods. Each microphone is generally designed to accept one method to power all of its components. The caveat is that some microphones can also be battery-powered.

Of course, the voltage that powers the microphones is derived from either the power mains or, in rare cases, batterie(s).

Mics are typically powered via the same cable that carries their audio. This is true of phantom power, DC biasing, T-power, Plug-in power, USB power, and is often the case with external power supply units (though these cables typically have additional pins designated to carrying power).

We’ve already listed the methods of powering microphones. Before we get into each method in detail, let’s talk about active microphones and their active components.


What Active Microphone Components Require Power?

So we know that certain microphones require power to function properly. These mics include all condensers and some ribbon mics that have built-in amplification circuits.

This answers our question about one of the components that require power (the internal preamps) but there are more active components in microphones that require power. They are as follows:

Let’s discuss each of these active components in more detail.

Vacuum Tubes (Impedance Converter)

Vacuum tubes act as impedance converters and pseudo-amplifiers in tube microphones.

Originally, tubes were required when building condenser microphones for their impedance converting capabilities. Transistors (particularly field-effect transistors), which we’ll discuss next, have largely replaced tubes in condenser microphone design.

So how does a vacuum tube work in a tube microphone? Let’s discuss the vacuum tube in the context of a tube condenser microphone.

The condenser capsule naturally outputs an audio signal with extremely high impedance. In the case of a tube mic, the vacuum tube is designed into the mic in order to drop the signal’s impedance so that the signal can be effectively sent through the rest of the mic circuitry; out the mic output; down the mic cable, and to wherever else the signal must go.

How do vacuum tubes convert impedance? Let’s take a look at the simplest microphone tube design: the triode.

Triodes, like all vacuum tubes, are designed with electrodes inside a tube. There is a vacuum in the tube and so no air is inside the tube.

The differentiating factor with a triode tube is that it has three electrodes. Together with the heater, the tube is made of the following:

  • Glass or ceramic tube.
  • A: Anode (positive electrode).
  • K: Cathode (negative electrode).
  • G: Grid (modulating electrode).
  • H: Heater.

Here is a simple diagram of a triode vacuum tube:

The external power supply unit effectively heats up the heater of the tube which, in turn, heats the vacuum tube. This heat is essential in the proper functioning of the tube. It’s also critical that the vacuum exists within the tube so that heater doesn’t burn itself up along with the electrodes.

Once heated, the cathode begins emitting electrons. Electronics are negatively charged and so naturally they are repelled by the cathode and attracted to the anode. Therefore, heating up the tube causes the flow of electrons between the cathode and anode which means that there is an electrical current within the tube.

The gate can be thought of as a high-impedance input that is capable of accepting the ridiculously high-impedance signal from the capsule.

At the grid, the connected signal from the capsules causes opening and closing in a continuous coinciding fashion. This grid activity causes a proportionate change in the flow of electrons from the cathode to anode.

So by applying a [high-impedance] signal at the gate, we are able to effectively modulate a lower-impedance (and often higher amplitude) signal for the tube to output.

To learn a great deal more about tube microphones, check out my article What Is A Tube Microphone And How Do Tube Mics Work?

FET/JFETs (Impedance Converter)

Transistors have largely replaced vacuum tubes in electrical circuits around the world. Microphone technology is no different.

FETs or JFETs (field-effect transistors or junction-gate field-effect transistors, respectively) act as impedance converters and pseudo-amplifiers similarly to vacuum tubes.

The big differences between FETs and tubes are in the lower power requirements; cheaper manufacturing costs; smaller size, and relative durability.

In terms of powering solid-state impedance converters, they can accept power from any of the above methods. Common methods include phantom power, DC biasing, and USB power (for USB mics).

The JFET transistor has three terminals (source, drain, and gate). These terminals are loosely analogous to the electrodes of a triode vacuum tube (anode, cathode, and grid, respectively).

To learn more about the similarities (and differences) between FET and tube mics, check out my article What Are The Differences Between Tube & FET Microphones?

Let’s quickly run over the basics of how a JFET works, starting with a simple diagram:

  • S: source.
  • D: drain.
  • G: gate.

The JFET is powered by a DC voltage applied across its source and drain terminals.

The capsule’s output signal, which has a very high impedance, is connected to the gate and source terminals. We can think of the gate as the high-impedance input.

The gate-source signal effectively modulates the current between the source-drain terminals. The source-drain can be thought of as the JFET’s output and has a much lower impedance (and often higher amplitude) than the modulating signal at the gate.

That’s basically how transistor-based impedance converters work in solid-state condenser microphones.

For a detailed read on FET/solid-state microphones, check out my article What Are FETs & What Is Their Role In Microphone Design?

Externally-Polarized Condenser Capsules

Condenser microphone capsules are essentially parallel-plate capacitors and work on electrostatic principles. The front plate is the moveable diaphragm and the backplate is stationary (and known simply as the backplate).

When holding a fixed charge, any change in capacitance causes a proportional change in voltage across the plates. Capacitance changes as the diaphragm moves and the distance between the plates changes.

So as the diaphragm moves, a coinciding mic signal is produced.

But this is only the case when the capsule holds a fixed charge. With externally-polarized condenser capsules, this polarizing voltage comes from the power source. These power sources are generally external power supply units (with tube mics) or phantom power (with FET mics).

The famous AKG CK 12 capsule is externally-polarized. This capsule is regularly referenced as a basis for condenser capsule design.

CK 12 Externally-Polarized Capsule

To learn more about microphone capsules, check out my article What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules).

Internal Preamplifiers

Microphone capsules/elements create relatively weak audio signals. In some microphones, active internal preamps help to boost the signal to a healthier lever before being outputted.

These internal preamps can be powered via any of the methods in this article.

Analog-To-Digital Converters

Microphone transducers are inherently analog in the way they convert mechanical wave energy (sound waves and diaphragm movement) to electrical energy (analog audio signals).

Digital microphones (those microphones that output digital audio) have built-in analog-to-digital converters that effectively change the analog signals from the mic transducer into the digital audio the mic will output.


Microphone Powering Methods

Now that we understand the essentials of active microphones and the active components within microphones, we have a solid foundation of knowledge to build upon when discussing the various microphone powering methods.

Microphone powering methods include:

Let’s talk about each of these methods in more detail.

External Power Supply Units

In the heyday of tube microphones, it was common for condenser microphones to have external power supplies. This is no longer the case since solid-state microphones have become more popular.

That isn’t to say that tube microphones today do not need external PSUs. Rather, all tube mics require external PSUs.

External power supply units often connect to their microphones using a multi-pin cable and connector. These PSUs are put in-line between the microphone and mic preamplifier and connect directly to the power mains.

Neumann U67 Tube Microphone
With Power Supply

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

External power supply units are typically used to power:

  • Vacuum tubes (impedance converter).
  • Externally-polarized condenser capsules.
  • Internal preamplifiers.

Phantom Power

Phantom power (P48) is the most common method of powering studio-grade condenser microphones (and active ribbon microphones). It is relatively safe (particularly with mics that do not require it) and uses the same balanced cable that carries the balanced audio signal from the microphone to the mic input of the preamplifier.

The phantom power is +48 volts DC carried on pins 2 and 3 of a balanced cable (typically XLR) relative to pin 1. Though 48 V is the standard (DIN 45596), some sources provide as low as 12 volts DC and others as high as 52 volts DC.

The term “phantom power” comes from the fact that P48 is sent through the same balanced audio cable that carries the microphone’s audio. P48 doesn’t cause any difference in the audio signal and there is no obvious power cable that supplies the microphone with its necessary power. It’s as if the mic is powered by a phantom!

Because phantom power applies a common DC voltage on the two audio pins of a balanced cable, it can be sent to microphones without affecting the audio signal of the mic whatsoever. Balanced audio is based on the differences between pins 2 and 3 and actually eliminates the commonalities on both audio pins via common-mode rejection.

Phantom power is typically sent via the balanced microphone preamp with an on/off switch. If your preamp doesn’t have a P48 option but your mic needs phantom power, there are standalone supply units available on the market that are fairly inexpensive.

One such supply is the Neewer 1-Channel Phantom Power Supply (link to check the price on Amazon):

Neewer 1-Channel Phantom Power Supply

Phantom power is typically used to power:

  • JFETs (impedance converter).
  • Externally-polarized condenser capsules.
  • Internal preamplifiers.

For everything you need to know about microphones and phantom power, check out my article What Is Phantom Power And How Does It Work With Microphones?

DC Biasing

Bias voltage is a low DC voltage (typically between 1.5 and 9.5 volts DC) that runs along the audio (and return) lines of an unbalanced mic cable.

This low DC voltage is used to power miniature electret microphones. In particular, DC bias is used to power the JFET impedance converters of small electret mics. The only active component in these unbalanced microphones is the JFET impedance converter, which can easily be powered by DC biasing.

DC biasing is typically used to power:

  • JFETs (impedance converter).
  • Internal preamplifiers.

T-Power (A-B Power)

T-Power (T12) is a standard written in DIN 45595.

It was one of the first methods to power condenser microphones directly through their audio cables. Since then, phantom power has effectively replaced T-power as the standard microphone powering technique due to its superior powering and safety.

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.

T-Power is typically used to power:

  • JFETs (impedance converter).
  • Externally-polarized condenser capsules.
  • Internal preamplifiers.

Plug-In Power

Plug-in-power (PiP) is covered by Japanese standard CP-1203A:2007 and the IEC 61938.

Plug-in-power is a common method to power consumer-grade electret microphones that connect to consumer audio equipment (portable recorders, computer sound cards, etc.).

PiP 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.

Plug-in power was widely used to power:

  • JFETs (impedance converter).
  • Internal preamplifiers.

USB-Power

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

In USB condenser microphones, USB power is used to power both the FET impedance converters and the analog-to-digital converters (note that all USB condenser capsules are pre-polarized electrets). In dynamic USB mics, the USB power is used only to power the ADC.

USB power is typically used to power:

  • JFETs (impedance converter).
  • Internal preamplifiers.
  • Analog-to-digital converters.

To read about my recommended USB mics, check out My New Microphone’s Top 9 Best USB Microphones (Streaming, PC Audio, Etc.).

Batteries

Some microphones are designed to run on power supplied by batteries. These mics will typically have an option to power the microphone with batteries or directly with one of the above-mentioned techniques.

Note that, when possible, most manufacturers actually advise users not to rely on battery power. It’s also advised that, with mics that have a battery option, we remove the batteries while the mic is powered by the other method to avoid potential battery leakage and the damage that comes with it.

One such battery-powered microphone is the Beyerdynamic MCE72 (link to check the price on Amazon):

Beyerdynamic MCE72

Batteries are typically used to power:

  • JFETs (impedance converter).
  • Internal preamplifiers.

Related Questions

How are dynamic mics powered? Dynamic microphone transducers work on the principle of electromagnetic induction and are, by nature, passive and do not require power to function. However, some dynamic ribbon microphones have active internal amplifiers and can be powered by phantom power, external power supplies, and by other means.

Are there magnets in microphones? Dynamic mic transducers (moving-coil and dynamic) work on the principle of electromagnetic induction and absolutely require magnets to function. The magnets in dynamic mics provide the permanent magnetic field necessary for the transducers to convert sound waves into electrical audio signals.

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