The Complete In-Depth Guide To Tube Condenser Microphones

Though tubes have largely been replaced by transistors in the vast majority of electrical circuits, they are still sometimes used (and often cherished) in the audio industry and in microphones. In fact, many of the greatest microphones to ever be produced are tube condenser microphones!

What is a tube condenser microphone? A tube condenser microphone is an active mic transducer that converts sound (mechanical wave energy) into audio (electrical energy) via a condenser capsule and vacuum tube electronics. Tube mics are loved for their warm character and accurate sound pick up and are sought after in studios around the world.

In this complete in-depth guide to tube condenser microphones, we’ll discuss everything you need to know about tube mics and, hopefully, answer any questions you have along the way!

Table Of Contents

What Is A Tube Condenser Microphone?

The definition of tube condenser can be as easy as unravelling its name: a tube condenser microphone is simply a condenser microphone with tube electronics. That’s too easy, though, so let’s dive into each of these descriptions in more detail.

What Is A Condenser Microphone?

A condenser microphone is an active mic (it requires power) that converts sound into audio via electrostatic principles and a capsule that acts as a parallel-plate capacitor.

There are many types of condenser microphones (including tube condensers). The key component that makes a microphone a “condenser” is the capsule, so let’s discuss the condenser capsules here.

AKG CK12 (left) and Neumann K67 (right) condenser capsules

The condenser capsule is effectively a parallel-plate capacitor. One plate is a movable membrane (known as the front plate or the diaphragm) and the other plate is stationary (known as the backplate).

The condenser capsule must hold a permanent electrical charge. In the case of tube microphones, this charge is supplied by an external power supply. In other mics, the charge may be supplied via phantom power or the capsule may even be permanently charged with electret material.

In order to hold the fixed charge necessary for proper capsule functioning, the capacitor must have incredibly high impedance so that the charge doesn’t drain away.

As the diaphragm moves back and forth, the capacitance of the capsule changes. When the capacitor holds a fixed charge, this change in capacitance causes an AC voltage (mic signal) to be produced.

What Are Tube Electronics?

Tube electronics are any electronics that involve a vacuum tube (otherwise known as a valve, thermionic tube or electron tube). A vacuum tube is a device that controls the flow of electric current in a vacuum between electrodes when a voltage has been applied. The term “tube” comes from the fact that the device looks like a sealed ceramic or glass tube.

In tube microphones, the basic tube is a triode tube which means the tube has three distinct electrodes. Triodes are famously known for their amplification abilities as we’ll find out soon.

Telefunken AC701 Triode Vacuum Tube

Remember how the condenser microphone capsule has an incredibly high impedance and outputs a signal with high impedance? Well, the vacuum tube is used primarily to drop (convert) this signal impedance so that the mic signal can be properly used. The vacuum tube also acts to amplify the signal level.

The tube is heated up via the external power supply unit and begins emitting an electrical current. This electrical current is effectively modulated by the capsule’s high-impedance low-level output signal. The modulated low-impedance high-level current/voltage ultimately becomes the outputted microphone signal.

Tube electronics are cherished for the colour they add to audio signals. A tube will naturally compress the audio signal and add slight harmonic saturation/distortion that is sonically pleasing to the ear.

6072A 12AY7EH Electro-Harmonix
Dual-Triode Tube

Recap On The Definition Of A Tube Condenser Microphone

Now that we know what a condenser microphone is and what tube electronics are, we have a good idea of what a tube condenser mic is.

A tube condenser microphone acts as a transducer, converting sound into audio via an electrostatic condenser capsule. This audio signal is then sent to a vacuum tube to convert the impedance and boost the level of the signal.

To reiterate, the 2 key takeaways here are that tube condenser microphones have:

  • Condenser capsules.
  • Tube electronics.

We’ll discuss the inner workings of tube condenser microphones in the section How Do Tube Condenser Microphones Work? but first, let’s go over a bit of the history of tube condensers. It wouldn’t be a complete guide without history, would it?

A Bit Of History On Tube Condenser Microphones

Let’s start at the very beginning with the invention of the vacuum tube.

Brief History Of The Vacuum Tube

In 1904, Sir John Ambrose Fleming, an English electrical engineer and physicist, invented the first vacuum tube. This tube was a diode which means it had two electrodes.

In 1905, Lee De Forest, an American inventor, came up with the first triode vacuum tube (with three electrodes including the control grid). The triode design allows the tube to act as an amplifier and is, to this day, the basic tube type used in microphones. This patent was awarded in 1906.

By the 1920s, vacuum tubes had become widely used in electrical circuits and technology. Microphone manufacturers had begun experimenting with vacuum tubes in their microphone designs.

Brief History Of The Condenser Microphone

In 1916, Edward Christopher Wente, an American physicist, invented the first-ever condenser microphone while working at Western Electric.

This microphone was designed with two plates: the front plate/diaphragm was thin and movable and the backplate was thicker and stationary. The two plates formed a capacitor (then referred to as a “condenser,” hence the name). A consistent voltage was applied across the plate to hold a fixed charge.

As the diaphragm moved, the distance between the plates changed which altered the capacitance of the parallel-plate capacitor.

By maintaining a fixed charge across the plates, any change in capacitance caused an inversely proportional change in voltage. Therefore, the moving diaphragm caused a coinciding AC voltage (mic signal) to be outputted from the mic.

Brief History Of The Tube Condenser Microphone

In 1928, Georg Neumann made microphone history (as he and his company, Neuman GmbH, often do) when they released the first-ever commercially available condenser microphone.

This microphone was the CMV3, better known as “The Bottle.”

Neumann CVM3

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

The CMV3 featured interchangeable capsules in order to achieve different polar patterns. It was designed with RE084 triode-based tube electronics.

Since then, microphone manufacturers around the world have been producing high-quality tube condenser microphones for the audio industry.

A Brief History Of Transistors

Vacuum tubes remained incredibly popular in electrical circuits until they were largely replaced by cheaper, smaller and more efficient transistors.

In 1947, American physicists at Bell Laboratories (John Bardeen, Walter Brattain, and William Shockley) invented the first-ever point-contact transistor.

Field-effect transistors would not show up practically in microphone technology until the mid-1960s but have become standard in condenser microphone design ever since their introduction.

Many modern condenser microphones are solid-state. In other words, they use transistor-based electronic circuits rather than tube-based electronic circuits. As mentioned, transistors are cheaper, more efficient, smaller, and aa an added bonus they often sound “cleaner” than tubes.

With that being said, tube microphones remain highly sought after for their wonderful characteristics and sound quality.

For a detailed account of microphone history, please consider reading through my in-depth article: Mic History: Who Invented Each Type Of Microphone And When?

How Do Tube Condenser Microphones Work?

In the section on What Is A Tube Condenser Microphone? we went over the basics of condenser capsules and tube electronics.

In this section, we’ll go through the inner workings of a tube condenser microphone in greater detail.

Of course, no two tube microphone models are the same but most follow a general pattern of components. These components are shown in the simplified diagram below:

Tube Condenser Microphone Diagram

The main components in a tube condenser microphone are as follows:

  • Condenser capsule
  • Vacuum tube
  • Printed circuit board
  • Power supply unit
  • Output transformer
  • Output connector

Let’s go through each of these components more comprehensively, shall we?

The Condenser Capsule

The condenser capsule is the transducer element of the tube condenser microphone. Transducers are devices that transform one form of energy into another. The capsule, then, is the part of the tube condenser mic that is responsible for converting sound waves (mechanical wave energy) into audio signals (electrical energy).

In order to convert sound into audio, the condenser capsule relies on electrostatic principles. In fact, condenser microphones were, and sometimes still are, referred to as “electrostatic microphones.”

For more microphone terminology, check out My New Microphone’s Glossary Of Microphone Terminology.

With that in mind, let’s discuss the structure of the condenser capsule. The typical capsule is made of the following components:

  • Diaphragm (front plate)
  • Backplate
  • Tensioning ring
  • Spacers
  • Electrical lead wires
  • Housing

Note that some capsules have two diaphragms and even two backplates in their design. More on these designs in the Multi-Pattern Tube Condenser Microphones section.

To better visualize the condenser microphone capsule, let’s take a look at a simple diagram that shows the essentials:

  • Diaphragm: the diaphragm acts as the movable front plate of the parallel-plate capacitor. It is a thin membrane often made of gold-sputtered Mylar.
  • Backplate: the backplate is the second plate of the capacitor and is stationary. It is often made of brass and is typically perforated with through-holes that allow sound to reach the rear of the diaphragm.
  • Tensioning Ring: the tensioning ring effectively holds the diaphragm in place while applying the appropriate tension.
  • Insulated Spacer Ring: the insulated spacer ring is designed to keep some space between the two plates while also providing insulation between them. This is required to maintain the capacitor design.
  • Backplate Mounting Ring: the backplate mounting ring holds the backplate in place.

The entire capsule is then housed in an outer shell and two electrical lead wires are taken from the capsule: one from the diaphragm (front plate) and the other from the backplate. These lead wires complete a circuit with the impedance converter (which is the vacuum tube in the case of tube condenser microphones).

How Does The Condenser Capsule Work?

Now that we know the basic design of the condenser capsule, we can get into how it works.

Sound waves cause localized pressure variation in the medium they travel through. The diaphragm of the capsule reacts to the difference in pressure between its front side and its rear side that is caused by these sound waves.

As an aside, directional condenser capsules work on the pressure-gradient principle which has both sides of the diaphragm exposed to sound pressure variation. Omnidirectional condenser capsules, conversely, work on the pressure principle and only have their front sides exposed to sound pressure variation.

To learn more about pressure and pressure-gradient mics, and directional and omnidirectional mics, check out the following My New Microphone articles:

Pressure Microphones Vs. Pressure-Gradient Microphones
A Complete Guide To Directional Microphones (With Pictures)
What Is An Omnidirectional Microphone? (Polar Pattern + Mic Examples)

Rode HF6 Cardioid Condenser Capsule

So how does this diaphragm movement translate to a microphone signal? To answer this question, let’s have a look at two critical electrostatic equations:

  1. V = Q • C
  2. C = ε0(A/d)

V = Q • C

The voltage across a parallel-plate capacitor is equal to the product of the electrical charge across the plates and the capacitance of the capacitor itself.

  • V = voltage across the plates.
  • Q = electrical charge between the plates.
  • C = capacitance of the parallel-plate capacitor.

Note that this equation is an ideality and that certain inefficiencies cause losses of voltage, charge and capacitance. However, this equation, in theory, holds true.

So the condenser capsule (parallel-plate capacitor) must be electrically charged in order to function properly.

In order to hold a charge, the plates of the capacitor must be electrically conductive. As mentioned, the diaphragm is often made of gold-sputtered Mylar. The Mylar is very reactive to sound pressure while the gold is conductive. The backplate is often brass, which is conductive. These plates must be insulated from one another.

To be more specific, the condenser capsule must hold a fixed electrical charge to function properly. Therefore, the capsule is designed with an incredibly high impedance to mitigate any leakage of electrical charge.

This unfortunately also means that the mic signal (AC voltage) across the plates will also have an especially high impedance. The vacuum tube is put there, in large part, to drop the impedance of the signal so that the signal may be sent out of the microphone without severe degradation.

A high signal impedance will critically deteriorate an audio signal through any significant length of cable. This is why the vacuum tube impedance converter is designed to fit immediately after the capsule in tube condenser microphone design.

For more information on microphone impedance, check out my article Microphone Impedance: What Is It And Why Is It Important?

This charge (aka “polarization”), in tube condenser microphones, is supplied via the external power supply unit (PSU). A portion of the power sent to the microphone is used to charge up the capsule for proper functioning.

As we can see from the equation V = Q • C, a fixed charge (Q) means that any change in capacitance will cause an inversely proportional change in voltage across the plates. This changing voltage will effectively be the mic signal. This brings us to our second electrostatic principle/equation.

C = ε0(A/d)

The capacitance of a condenser capsule is equal to the product of the dielectric constant, and the quotient of the area of the plates and the distance between the plates.

  • C = capacitance of the parallel-plate capacitor.
  • ε0 = dielectric constant.
  • A = area of the plates.
  • d = distance between the plates.

This equation is also an ideality so inefficiencies cause losses in some of the factors.

The dielectric constant and the area of the plates are both constant. Therefore, we can simplify the equation to state that the capacitance of the mic capsule is inversely proportionate to the distance between the plates.

Combining what we know of the two electrostatic equations, we infer that the voltage across the capsule is dependent on the distance between the capsule plates. Further inference tells us that a moving diaphragm will cause a proportionate change in voltage across the plates.

As discussed, the diaphragm moves according to sound waves. Thus the microphone represents the sound waves as an AC voltage (aka audio signal). This is how the capsule works as a transducer.

My New Microphone has plenty of articles on condenser capsules and diaphragms. Consider reading any of the following articles for more information:

What Is A Microphone Capsule? (Plus Top 3 Most Popular Capsules)
What Are Centre And Edge-Terminated Microphone Capsules?
Why Are Condenser Microphone Diaphragms Gold-Sputtered?
Large-Diaphragm Vs. Small-Diaphragm Condenser Microphones
What Is A Microphone Diaphragm? (An In-Depth Guide)

The Vacuum Tube

It wouldn’t be a tube condenser microphone with a vacuum tube. Let’s discuss how vacuum tubes work in the context of microphones.

We’ll start with a simple diagram of a triode tube. Triode tubes have 3 electrodes and are the simplest form of a microphone vacuum tube:

Note that many tubes with greater electrode counts are only configured as triodes when used in tube condensers.

Triode Vacuum Tube Diagram
  • A: Anode (plate)
  • K: Cathode
  • H: Heater
  • G: Grid

The power supply unit of the tube condenser microphone causes the heater of the tube to heat up. This is why tube condensers get so warm when they are in use.

Note that the tube must hold a vacuum (no air), otherwise the heat, combined with oxygen, would burn up the elements. Any air in a vacuum tube would also interfere with electron movement and make the tube much less efficient.

The power supply also applies a positive voltage to the anode (plate).

As the tube heats up, the cathode (electron donor) begins shedding electrons via thermionic emission. These negatively charged electrons are repelled by the negatively charged cathode and attracted to the positively charged anode (plate).

Since the tube contains a vacuum, the electrons flow unimpeded between the cathode and anode. This flow of electrons is better known as an electrical current.

Once heated and powered, the vacuum tube will effectively “output” a voltage.

The grid electrode is where things get really interesting for the microphone design.

The control grid acts as a sort of mesh between the cathode and anode. Its holes allow electrons to pass through it. By adjusting the voltage applied to the grid, we control the number of electrons flowing from the cathode to the anode and modulate the voltage across the vacuum tube.

The control grid effectively accepts the high-impedance signal from the condenser capsule. This AC signal at the grid modulates the stronger signal at the plate.

This makes the triode tube invaluable not only as an amplifier but also as an impedance converter. With a triode, we use the high-impedance capsule signal (at the “input” or grid of the tube) to modulate a stronger low-impedance signal (at the “output” or plate of the tube).

The Printed Circuit Board

The printed circuit board of the condenser tube microphone is designed to effectively send electricity where it needs to go. There are specific paths the mic signal must take and other paths for the polarization voltage and positive anode voltage from the power supply. A printed circuit board also provides a proper grounding path and ground potential.

Additionally, the PCB may also feature switches in its circuitry. These switches may include pads, filters, polar pattern changes, etc. These switches may also be part of the power supply unit depending on the microphone, which brings us to our next section.

To learn more about pads, filters and polar patterns, read the following My New Microphone articles, respectively:

What Is A Microphone Attenuation Pad And What Does It Do?
What Is A Microphone High-Pass Filter And Why Use One?
The Complete Guide To Microphone Polar Patterns

The Power Supply Unit

Each tube microphone has its own power supply unit. These PSUs plug into the wall and provide their tube condenser with the appropriate voltages for proper functionality.

As mentioned above, the PSUs are essential in order to polarize the condenser capsule; charge the anode (plate) positively, and heat up the heater of the vacuum tube.

Note that the +48V DC from phantom power is incapable of running the tube electronics of tube condenser microphones. It does not supply enough voltage.

As we’ll get to shortly in The Output Connector section, the PSUs often connect to the microphone via the output connector of the mic. This means that the PSU will oftentimes (but not always) also receive the mic signal. In this case, the PSU will have a balanced mic output to effectively connect the microphone to a mic preamplifier.

The Legendary AKG C 12 Tube Condenser
With Its Power Supply Unit

In the above-picture AKG C 12 power supply unit, we see the power switch as well as two dials that are used to change the microphone’s high-pass filter and polar patterns remotely.

The Output Transformer

Many (but not all) tube microphones utilize an output transformer in their design.

Transformers are passive electromagnetic devices that transfer energy from one circuit to another by means of inductive coupling.

Basically, each circuit has its own conductive winding (wire) that wraps around a common magnetic core. This effectively couples the two circuits.

Inductively coupled circuits, like those in transformers, are configured so a change in current through one circuit’s conductor/winding induces a voltage across the other circuit’s conductor/winding.

Most transformers used in tube condensers are step-down transformers. These transformers fulfill the following roles:

  • Decrease/convert the output impedance.
  • Block DC voltage from entering the sensitive microphone components.
  • Balance the tube’s outputted audio signals.
  • Colour the microphone’s output signal.
  • Decrease the output voltage.

Here is a simple diagram of a step-down transformer. We will use this diagram to explain tube condenser output transformers in greater detail:

Step-Down Transformer
  • P = primary winding: the primary winding creates a circuit with the vacuum tube and printed circuit board. This means the capsule’s converted signal affects the primary winding.
  • S = secondary winding: the secondary winding creates an open circuit with the microphone output. This circuit is completed when the tube condenser microphone is plugged in.
  • MC = common magnetic core: in order for inductive coupling to work, we need electromagnetic induction. The voltage across the primary winding causes a changing magnetic field within the magnetic core which then induces a voltage across the secondary winding.

In the step-down transformer, we have more turns in the primary winding than in the secondary winding. This does a few things:

  • Drops the voltage:
    Vs = (Ns/Np) ⋅ Vp
  • Increases the current:
    Is = (Np/Ns) ⋅ Ip
  • Decreases the impedance:
    Zs = (Ns/Np)2 ⋅ Zp

So, basically, a voltage across the primary winding (due, ultimately, to the mic capsule) causes a change in the magnetic core’s magnetic field. This change in the magnetic field then induces a voltage across the secondary winding. This is all due to electromagnetic induction.

Transformers are used primarily to balance the inherently unbalanced signal from the tube and PCB. The transformer’s secondary winding effectively “outputs” a positive polarity AC signal on one pin and that same signal in negative polarity on another pin when connected to the microphone’s output.

This causes a balanced audio signal which is resistant to electromagnetic interference and capable of travelling long distances through balanced cable without degrading significantly.

To learn more about balanced audio and microphones, check out my article Do Microphones Output Balanced Or Unbalanced Audio?

Another big effect of the step-down transformer is that it acts as a second impedance converter stage. With a transformer, we can take some of the load off the tube electronics and still achieve a usable output impedance in our tube condenser mics.

Note that transformers only pass alternating current and block direct current. This is known as DC isolation and helps to protect the tube electronics from stray DC voltage on the audio signal lines.

Yet another characteristic of transformers is their colouration. The inductive coupling is not perfect and actually adds colour and distortion to the mic signal. In cheap transformers, this colouration can sound absolutely awful. However, in the expensive transformers commonly used in tube condensers, the effect is actually quite pleasing to the ear.

For more information on microphone transformers, check out my article What Are Microphone Transformers And What Is Their Role?

A Note On Transformerless Tube Condenser Microphones

There have been many advancements in electrical circuit theory since the invention of the transistor. Since then it has become possible to design microphones that would normally require an output transformer with a transformerless output circuit instead. These transformerless outputs act to balance the signal and adjust the output impedance.

There are many solid-state condenser mics with transformerless outputs but it is less common in tube condenser microphones.

A modern example of a transformerless tube condenser microphone is the Neumann M 150 Tube (link to check the price on Amazon).

Neumann M 150 Tube Condenser Mic

The Neumann M 150 Tube uses an op-amp based output circuitry (with transistors) to balance and convert the impedance of its output signal.

The Output Connector

Most professional microphones have XLR output connectors. This is not the case with tube condensers.

Tube condenser microphones have all sorts of different output connectors. The connectors typically connect the microphone to its dedicated power supply unit and most tube mic manufacturers design mic-specific connections to fulfill this purpose.

The 7-pin XLR is a common output connector choice for tube microphones. Tuchel connectors have also been used regularly throughout the history of tube condensers.

With 7 pins, we could have the following configuration:

  1. Audio (positive polarity)
  2. Audio (negative polarity)
  3. Heater Send
  4. Heater Return
  5. Anode (plate) DC bias
  6. Plate return
  7. Ground

This is only one potential way a cable could be wired. Not all tube condenser output connections are wired the same. In fact, it’s a safe bet to assume that any two tube condenser microphones will have differing output wiring schematics.

To learn more about microphone output connections, check out my article What Do Microphones Plug Into? (Full List Of Mic Connections).

Multi-Pattern Tube Condenser Microphones

In 1948, Georg Neumann brought another first to the microphone market. The legendary Neumann U 47 (with selectable omnidirectional and cardioid polar patterns) was the first-ever multi-pattern microphone. This mic, as we can expect from the title of this section, was a tube condenser microphone.

The U 47 utilized the dual-diaphragm M7 capsule in order to achieve its cardioid and omnidirectional polar patters.

Neumann M7 Condenser Capsule

Since 1948, manufacturers have been producing multi-pattern tube condenser microphones. Many of the most popular and beloved tube condensers are multi-pattern microphones.

So how do multi-pattern tube condenser microphones work?

Let’s start off by stating that it has nothing to do with the vacuum tube of the microphone. Rather, the multi-pattern functionality comes from the microphone capsule.

The capsule of a multi-pattern mic must have two diaphragms. This is relatively easy to achieve with a condenser capsule. The two diaphragms are placed on the outsides of the disc-shaped capsule. They can even share a backplate though some designs have two individual backplates as well.

This design effectively yields two back-to-back capsules within a single capsule design.

These two transducers are nearly always designed to have cardioid polar patterns. To do so, there must be carefully designed acoustic labyrinths that allow sound to reach the rear of both diaphragms.

Neumann K67 Dual-Diaphragm Centre-Terminated Condenser Capsule

By polarizing the two parallel-plate capacitors in varying configurations, we can achieve different polar patterns.

Let’s have a look at the 3 most common options we’ll find in a multi-pattern microphone:

  • Omnidirectional: this pattern is achieved by polarizing both transducers with the same voltage and the same polarity. The two cardioid patterns come together to capture sound equally from all directions.
Omnidirectional Polar Response Graph
  • Bidirectional: this pattern is achieved by polarizing both transducers with the same voltage but in the opposite polarity to one another. This effectively causes the front diaphragm to pick up sound in positive polarity and the back diaphragm to pick up sound in negative polarity. The pick up of the sides effectively cancel each other out and we’re left with a bidirectional polar pattern.
Bidirectional Polar Response Graph
  • Cardioid: this pattern is achieved simply by polarizing only the front transducer of the capsule. Note that the polarizing voltage is typically higher, in this case, to ensure the cardioid pattern is as sensitive as the other patterns that utilize both diaphragms.
Cardioid Polar Response Graph

To learn more about the omnidirectional, bidirectional and cardioid polar patterns, check out the following My New Microphone articles, respectively:

What Is An Omnidirectional Microphone? (Polar Pattern + Mic Examples)
What Is A Bidirectional/Figure-8 Microphone? (With Mic Examples)
What Is A Cardioid Microphone? (Polar Pattern + Mic Examples)

The most famous multi-pattern capsule in the world was actually developed in response to the U 47. This capsule was designed by AKG and is known as the CK12.

This image has an empty alt attribute; its file name is mnm_300_AKG_CK12_capsule.jpg

Microphones that utilize the AKG CK12 (or a similar capsule) often boast a whopping 9 selectable polar patterns.

General Characteristics Of A Tube Condenser Microphone

Each and every microphone model has its own unique design, character, and pros and cons. However, there are some remarkable commonalities between tube condenser microphones that we should discuss here.

General characteristics of tube condenser microphones include:

  • Extended frequency response.
  • Saturated “warm” tone (distortion).
  • Naturally compressed.
  • High-sensitivity ratings.
  • Relatively high self-noise.
  • High price point.

Extended Frequency Response

Tube condenser microphones are cherished for their extended frequency responses. This is actually a commonality across all studio-grade condenser microphones and not just tube condensers.

The low mass and inertia of the capsule’s diaphragm allow sound frequencies across the audible spectrum to move the diaphragm easily. The relatively tight tensioning of the diaphragm also improves reactiveness to the wide range of frequencies.

The tension of the diaphragm also yields an accurate transient response at the capsule.

Though the tube electronics act to naturally compress these spikes in the mic signal, tube condensers certainly do have accurate transient responses along with their wide frequency responses.

The frequency response of a condenser microphone is more so determined by its capsule than by its circuitry. Small-diaphragm condensers tend to have flatter high-end frequency responses than their large-diaphragm counterparts because the high-frequency sound waves (with short wavelengths) are more effective at moving smaller diaphragms.

To learn more about microphone frequency response; transient response, and the differences between small-diaphragm and large-diaphragm condenser mics, check out the following My New Microphone articles:

Complete Guide To Microphone Frequency Response (With Mic Examples)
What Is Microphone Transient Response & Why Is It Important?
Large-Diaphragm Vs. Small-Diaphragm Condenser Microphones

Saturated “Warm” Tone

Vacuum tubes are loved in the audio world due to their “warm” sound.

This warmth is caused by 2 factors inherent in vacuum tube electronics:

  1. Thermal noise.
  2. Distortion/saturation.

Thermal noise refers to the phenomena where ambient heat causes electrons in conductors to vibrate and cause electrical noise. This noise occurs naturally in heated (functioning) vacuum tubes and is carried in the signal throughout the rest of the gain stages.

Thermal noise has a uniform power density which means it is equally present in all frequencies. In this way, it sounds like white noise.

Though noise is generally considered the enemy in audio signals, the broadband thermal noise in tube condenser mics, if not overly present, may add a certain warmth and smoothness to the tone of the microphone.

Saturation distortion refers to a subtle form of analog signal distortion. Vacuum tubes, when passing higher signal levels from the capsules, tend to saturate.

Audio saturation adds sonically-pleasing harmonics to the audio signal. Tube saturation helps to warm up the sound and has the added benefit of naturally compressing the sound, making it fuller and more present.

Naturally Compressed

Speaking of compression, I’ll restate here that tube electronics will act to compress the signal during saturation.

Compression effectively reduces the dynamic range of a signal (the difference between its strongest or loudest point and its weakest or quietest point). Compression actually brings the highest levels down (those that cause saturation) but the sonic effect is that of bringing the quieter parts up.

The result, as mentioned, is a full, smooth, and present sound. Tubes are loved by audio enthusiasts for this reason.

High-Sensitivity Ratings

The internal amplification of tube condenser microphones gives them high sensitivity ratings.

A microphone’s sensitivity rating/specification refers to its output level when subjected to a given sound pressure level. By having internal amplification, tube condensers are capable of outputting very strong signals at a given sound pressure.

For more information on microphone sensitivity ratings, check out the following My New Microphone articles:

What Is Microphone Sensitivity? An In-Depth Description
What Is A Good Microphone Sensitivity Rating?

Relatively High Self-Noise

The thermal noise of the tube amp causes relatively high self-noise ratings in the tube condenser microphones.

As mentioned, this isn’t always a bad thing but it is worth noting as a general characteristic of tube condenser microphones.

For an in-depth read on microphone self-noise, check out my article What Is Microphone Self-Noise? (Equivalent Noise Level).

High Price Point

High-quality condenser capsules, vacuum tubes and transformers are very expensive. When the components are that expensive, microphone manufacturers tend to not cheap-out on other electrical and housing components for their microphones.

This is even before research and development and the costs associated with manufacturing which further increase the cost.

In order to produce a profit, then, tube condenser microphones are sold at high price points as well.

On top of this, many of the greatest microphones in the world are vintage tube condensers that are no longer in production. These mics command a premium price point due to their collectability.

To learn more about vintage microphones, check out My New Microphone’s Top 12 Best Vintage Microphones (And Their Best Clones).

Applications Of Tube Condenser Microphones

In the early days of tube condenser microphones, the recording practices were much different. Music recording generally consisted of a single microphone placed in front of an entire group of musicians. Radio was a bit different, where a mic was placed in front of the single announcer.

Since then, many different practices have come about. Most notable among these practices is the idea of close-miking or otherwise isolating individual sound sources.

Tube microphone technology has continued to improve along with the recording industry. However, not much thought has to be put into redesigning tube condensers for specific applications. This isn’t an oversight though. It’s just that tube condenser microphones naturally sound amazing on practically all sound sources.

The following list includes some of the common tube condenser microphone applications:

  • Vocals.
  • Voiceover.
  • Room mics.
  • Brass.
  • Woodwinds.
  • Acoustic guitar.
  • Piano.
  • Orchestra.
  • Guitar & bass amps/cabinets.

To learn about my recommended microphones for each of the above applications, check out My New Microphone’s Recommended Microphones And Accessories.

There are many tube microphones included in My New Microphone’s Top 11 Best Microphones For Recording Vocals.

Tube Condenser Microphone Examples

In order to truly understand tube condenser microphones, it is essential that we have a look at some real-world examples. In this section, we’ll discuss 5 tube condenser microphones, focusing on their components and design as well as how they portray the general characteristics and applications of tube condensers.

The 5 microphones we’ll be discussing are currently on the market and are as follows:

  1. Telefunken Ela M 251E
  2. AKG C 12 VR
  3. Neumann M 150 Tube
  4. Sony C-800G
  5. Avantone Pro CV-12

Telefunken Ela M 251E

The Telefunken Ela M 251E (link to check the price at B&H Photo/Video) is a great example of a vintage tube condenser microphone. It was originally released in 1959 and has recently been put back into production.

This high-end side-address multi-pattern tube condenser microphone was based on another tube condenser legend: the AKG C 12.

Telefunken Ela M 251E
  • Debut year: 1959
  • Capsule: AKG CK-12
  • Vacuum tube: 6072a (General Electric or Electro Harmonix)
  • Transformer: Haufe T14:1
  • Power supply: M 950E
  • Polar patterns: Omnidirectional/ Cardioid/ Bidirectional
  • Frequency response: 20 Hz – 20,000 Hz
  • Sensitivity rating: 17 mV/Pa
  • Output impedance: 200 Ω (50 Ω switchable)
  • Self-noise: 9 dBA
  • Maximum sound pressure level: 130 dB SPL

The Telefunken Ela M 251, like most vintage microphones, captures audio with character. Though the 251 is accurate in its pick up, it gives incredible “warmth” and “weight” to the audio signal due in large part to its 6072a vacuum tube and Haufe T14:1 output transformer.

The Telefunken Ela M 251E is featured in the following My New Microphone articles:

50 Best Microphones Of All Time (With Alternate Versions & Clones)
Top 11 Best Microphones For Recording Vocals
Top 12 Best Vintage Microphones (And Their Best Clones)
Top 20 Most Expensive Microphones On The Market Today


The AKG C 12 VR (link to check the price on Amazon) is another microphone based on the legendary AKG C 12 (from 1953). This multi-pattern tube condenser offers the following options:

  • 9-selectable polar patterns
  • -10dB and -20dB pads
  • 100Hz (-6dB/octave) and 130Hz (-12dB/octave) high-pass filters

AKG’s C 12 VR uses the original 6072A vacuum tube and dual-diaphragm capsule design of the 1953 model. However, it incorporates an updated, edge-terminated CK12 capsule and a state-of-the-art circuit board for lower noise and distortion as well as increased reliability.

  • Debut year: 1994
  • Capsule: AKG CK-12
  • Vacuum tube: 6072A
  • Transformer: Ü66 (T5743)
  • Power supply: N12 VR
  • Polar patterns: 9-selectable
  • Frequency response: 30 Hz – 20,000 Hz
  • Sensitivity rating: 10 mV/Pa
  • Output impedance: 200 Ω
  • Self-noise: 22 dBA
  • Maximum sound pressure level: 128 dB SPL

The AKG C 12 VR captures audio with pristine accuracy while adding a pleasant character (“warmth” and “depth”) to the audio signal. This is mainly due to the 6072A vacuum tube and Ü66 output transformer components.

The AKG C 12 VR 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)

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

Neumann M 150 Tube

The Neumann M 150 Tube (link to check the price at B&H Photo/Video) is a bit different than the other tube condensers on this list.

To begin with, it’s a small-diaphragm condenser, unlike the other large-diaphragm condensers. Another key difference is that the M 150 Tube has a transformerless output circuit.

This microphone is based on Neumann’s vintage M 50 tube condenser, which was based on the legendary M 49 microphone. The M 50 and the M 150 Tube are known for their bright high-end and omnidirectional polar patterns.

The M 50 was made legendary from its use on orchestral recordings (particularly when used in overhead stereo miking techniques such as the Decca Tree) and the M 150 Tube follows directly in its footsteps.

Neumann M 150 Tube
  • Debut year: 2001
  • Capsule: K 33 TI
  • Vacuum tube: 6111
  • Transformer: N/A
  • Power supply: N 149 A or N 149 V external power supplies
  • Polar pattern: Omnidirectional 
  • Frequency response: 20 – 20,000 Hz
  • Sensitivity rating: 20 mV/Pa
  • Output impedance: 50 Ω
  • Self-noise: 15.0 dBA (28 dB)
  • Maximum sound pressure level: 114 dB

This microphone is very accurate and is considered to be bright (sensitive to high-end frequencies) compared to most tube condensers.

The Neumann M 150 Tube is featured in the following My New Microphone articles:

50 Best Microphones Of All Time (With Alternate Versions & Clones)

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

Sony C-800G

The Sony C-800G (link to check the price on Amazon) is a modern beast when it comes to tube condenser microphones.

This microphone has a large dual-diaphragm condenser capsule based on the Neumann K67 and is switchable between cardioid and omnidirectional modes.

The 6AU6 tube gives the C-800G part of its characteristic weight and sound. The mic is easily distinguishable by its large external heatsink that keeps the tube at an optimal temperature for perfect performance.

Sony C-800G
  • Debut year: 1993
  • Capsule: Sony C800G (based on Neumann K67)
  • Vacuum tube: 6AU6
  • Transformer: Custom T101 9:1
  • Power supply: AC-MC800G
  • Polar patterns: Omnidirectional and Cardioid
  • Frequency response: 20 Hz – 18,000 Hz
  • Sensitivity rating: 
    17.8 mV/Pa (Omnidirectional)
    25.1 mV/Pa (Cardioid)
  • Output impedance: 100 Ω
  • Self-noise: 18.0 dBA
  • Maximum sound pressure level: 131 dB SPL

The Sony C-800G is best known for its use as a hip-hop and R&B vocal microphone. It captures sound with natural clarity and remarkable body and presence. It enhances nearly every type of vocal it captures.

The Sony C-800G is featured in the following My New Microphone articles:

50 Best Microphones Of All Time (With Alternate Versions & Clones)
Top 11 Best Microphones For Recording Vocals
Top 20 Most Expensive Microphones On The Market Today

Avantone Pro CV-12

The Avantone Pro CV-12 (link to check the price at B&H Photo/Video) is an example of a “budget” tube condenser microphone with a price point of about $500 USD.

This microphone is also reminiscent of the AKG C 12 (we can tell by the name) and other vintage tube condensers from that era. It features a large 32mm Mylar diaphragm in an externally-polarized capsule and a 6072A tube for a warm, vintage tone and audio quality.

Avantone Pro CV-12
  • Debut year: 2006
  • Capsule: K67-styled capsule
  • Vacuum tube: 6072A dual-triode
  • Transformer: Custom
  • Power supply: PS-12
  • Polar patterns: 9-selectable
  • Frequency response: 25 Hz – 20,000 Hz
  • Sensitivity rating: 17.8 mV/Pa
  • Output impedance: 250 Ω
  • Self-noise: 17 dBA
  • Maximum sound pressure level: 146 dB SPL

This microphone, like all the tube condensers on this list, excels in practically all applications but is particularly effective on vocals.

The Avantone CV-12 is featured in the following My New Microphone articles:

Top 10 Best Microphones Under $500 for Recording Vocals

Differences Between Tube And Solid-State Condenser Microphones

The obvious difference between tube and solid-state condenser microphones is that the tube mics utilize vacuum tubes as their impedance converters while solid-state mics utilize transistors as their impedance converters.

This is a pretty big difference and actually results in other noteworthy differences. Let’s have a look at the main differences here:

 Tube MicrophonesFET Microphones
Impedance ConverterVacuum tube (at least a triode)Field-effect transistor (often JFET)
Power SourceExternal power supply unitsPhantom power or DC bias voltage
Audio QualityTypically warmer (tube saturation and high-end roll-off)Typically colder (accurate sound capture)
Transformer-coupled outputYesSometimes
DurabilityFragile tube componentsMore durable solid-state components
PriceVery expensiveLess expensive

To learn about the differences between tube and solid-state condenser microphones in greater detail, check out my article What Are The Differences Between Tube & FET Microphones?

Differences Between Dynamic And Condenser Microphones

It’s good to know the differences between tube and solid-state condensers. It’s best to also understand the contrast between condenser microphones and dynamic microphones. In the below table, consider tube condenser microphones in the “Condenser Microphones” column.

 Dynamic MicrophonesCondenser Microphones
Transducer PrincipleElectromagnetic inductionElectrostatic principles
Frequency ResponseColouredFlat/extended
Transient ResponseSlowFast
Polar PatternsAll but bidirectionalAll (especially with dual-diaphragm capsule)
Maximum Sound Pressure LevelOften too high to measureOften within practical limits
DurabilityVery durableSomewhat durable
PriceInexpensive to moderateCheap to very expensive

For more information relating to the differences between dynamic and condenser microphones, check out my detailed article titled Differences Between Dynamic & Condenser Microphones.

What is a microphone made out of? Different microphones are made with different components. Every mic, however, has a moveable diaphragm that reacts to sound waves and transducer element that converts this diaphragmic movement into an electrical audio signal. Other key components include grilles, bodies, transistors, transformers, and vacuum tubes.

To learn more about what microphones are made of and how they’re made, check out my articles What Are Microphone Diaphragms Made Of? (All Diaphragm Types) and How Are Microphones Made? (Designs, Materials, Production), respectively.

Can I plug a microphone into my phone? Yes, there is a wide variety of smartphones on the market with a large selection of microphones designed to connect to them. These mics usually connect via micro-USB, lightning, or 1/8″ (3.5 mm) TRRS and are often part of a headphone setup.

For much more information on smartphones and microphones, check out the following My New Microphone articles:

How To Connect An External Microphone To A Smartphone
How To Choose The Best Microphone For Your Smartphone Audio
Top 4 Best External (Lightning) Microphones For iPhone Audio
Top 4 Best External Microphones For Android Smartphones

This article has been approved in accordance with the My New Microphone Editorial Policy.


Recent Content