In my deeper research into how microphones work, I found that transformers and transistors are key components in many microphones.
Do all microphones have transformers? Although transformers are common in microphones, they are certainly not required. Nearly all passive ribbon and tube mics have output transformers. Many dynamic and condenser mics have transformers. Active ribbon and electret condenser mics rarely, if ever, have transformers.
Do all microphones have transistors? Transistors are essential in the circuitry of active microphones that do not utilize vacuum tubes. Transistors (often FET or JFETs) are found in active ribbon and non-tube condenser mics. They are not part of the design of passive mics or tube mics.
Why do some microphones use transformers and why do some microphones use transistors? Why do some mics use both while others use neither? This article will dive deeper into these questions.
Table Of Contents
- An Important Primer On Impedance And Microphone Output Levels.
- What Is A Transformer And What Is Its Role In A Microphone?
- What Is A Transistor And What Is Its Role In A Microphone?
- Do All Microphones Have Transformers And Transistors?
- Do Moving-Coil Dynamic Microphones Have Transformers?
- Do Moving-Coil Dynamic Microphones Have Transistors?
- Do Passive Ribbon Dynamic Microphones Have Transformers?
- Do Passive Ribbon Dynamic Microphones Have Transistors?
- Do Active Ribbon Dynamic Microphones Have Transformers?
- Do Active Ribbon Dynamic Microphones Have Transistors?
- Do Electret Condenser Microphones Have Transformers?
- Do Electret Condenser Microphones Have Transistors?
- Do “True” Condenser Microphones Have Transformers?
- Do “True” Condenser Microphones Have Transistors?
- Do Tube Condenser Microphones Have Transformers?
- Do Tube Condenser Microphones Have Transistors?
- Do Lavalier/Miniature Microphones Have Transformers?
- Do Lavalier/Miniature Microphones Have Transistors?
- Related Questions.
An Important Primer On Impedance And Microphone Output Levels
Before we get into the discussion of whether specific microphones and microphone types have transformers and/or transistors, it’s critical that we understand microphone impedance and outputs.
What is impedance? Impedance can be though of a electrical resistance against AC signals (like mic/audio signals). Electrical impedance impedes the flow of electrons in a circuits. For optimal AC signal transfer from one device to another, it’s critical for the source impedance to be a fraction of the load impedance.
As a rule of thumb, the source impedance should be at least 1/10th that of of the load impedance.
What are source and load impedance? It depends on our reference point.
- According to the microphone, the load impedance would be the input impedance of the next device connected in line (most often a preamp). The mic’s output impedance must be much smaller than the preamp’s input impedance (load impedance) for optimal signal flow.
- According to the mic preamp, the source impedance would be the output impedance of the connected microphone.
Professional microphones have low output impedances (range between 50 Ω to 600 Ω) in order to work well with professional mic preamplifiers.
However, microphone transducer elements (the mic diaphragm and capsule, cartridge, or ribbon baffle) do not always output signals with proper impedances. The same goes for the output signals of vacuum tubes within tube microphones.
Transformers and transistors both act as impedance converters. Depending on the microphone, they may increase or decrease the signal impedance in order to provide the proper microphone output impedance.
For more information on microphone impedance, check out my article Microphone Impedance: What Is It And Why Is It Important?
Microphone Output Levels
What is a microphone output signal? A microphone output signal is a mic level audio signal (an AC voltage generally between 1 to 10 millivolts or -60 to -40 dBV). It is an electrical representation of the diaphragm movement, which moves in response to sound waves. In pro mics, this signal is generally balanced and has low impedance.
Microphone output levels are most often understood through the mic sensitivity specification.
Mic sensitivity tells us the output signal strength of a microphone when the mic is subjected to a 94 dB SPL (1 Pascal) 1 kHz tone at its diaphragm.
The general microphone types have the following sensitivity ratings:
- Passive dynamic microphones: 0.5-6 mV/Pa (-66 to -44 dBV/Pa).
- Active ribbon and condenser microphones (both FET and tube mics): 8 and 32 mV/Pa (-42 dBV to -30 dBV/Pa).
These mic level signals require preamp gain in order to get boosted to line level signals. At line level, these audio signals work properly in professional gear (audio mixers, recorders, interfaces, etc.).
However, microphone transducer elements (the mic diaphragm and capsule, cartridge, or ribbon baffle) do not always output mic level signals. Often times they output low voltages that require both amplification and impedance conversion before they ever reach the microphone output connector.
Transformers and transistors both act to alter the microphone output levels. Most often this is to amplify the mic signal so that is does not depend on great amounts of preamp gain to get boosted to line level.
Another important note on microphone output signals is that professional microphones output balanced audio signals.
What is balanced audio? Balanced audio is a clean method of carrying audio on 3 conductors. Two conductors (pins 2 and 3 of a typical XLR mic output) carry the same audio signal but in reverse polarity to one another. The other conductor (pin 1) acts as ground.
At a balanced input, the differences between pins 2 and 3 are effectively summed together by a differential amplifier. This process yield a clean audio signal since the differential amp will cancel any noise that is identical on pins 2 and 3 (this is known as common-mode rejection).
Transformers can effectively convert an unbalanced signal (made of only a ground and a single signal conductor) into a balanced signal via a centre-tap on the secondary winding.
Transistors do not output balanced audio by default. The audio signal from a transistor can become balanced through the mic’s circuitry or via a transformer.
What Is A Transformer And What Is Its Role In A Microphone?
What is a transformer? A transformer is a passive electrical device that reduces or increases the voltage of an alternating current. Transformers do so via electromagnetic induction. Two conductive coils wrap around a magnetic core. The primary coil acts as the “input” voltage. The secondary coil, with more or fewer windings, “outputs” a stepped up or stepped down voltage.
A basic transformer is made of a single magnetic core and two windings of conductive coil (the primary winding and the secondary winding).
In the case of microphones, the primary winding is part of a circuit that carries the diaphragm’s signal. The secondary winding is part of the circuit that brings the “transformed” audio signal to the mic output.
It’s important to note that the windings do not touch one another, though they both wrap around the same magnetic core.
As AC runs through the primary winding, it induces a changing magnetic flux in the magnetic core. This changing magnetic flux then induces an AC voltage across the secondary winding.
The affect that an AC voltage has on magnetic flux (or vice versa) depends on three factors:
- The number of loops in the coil.
- The velocity of the coil through a magnetic field.
- The strength of the magnetic field.
The transformer windings are stationary and the magnet is permanent. Therefore, the only factor that (under ideal/lossless conditions) changes the voltage on the secondary winding compared to the primary is the number of loops in the coil.
This brings about 3 general possibilities:
- Step-up transformer: Step-up transformers have more turn on the secondary winding and increase (“step-up”) the voltage.
- Step-down transformer: Step-up transformers have fewer turns on the secondary winding and decrease (“step-down”) the voltage.
- Impedance transformer: Impedance transformers have the same number of turns in each winding. Under lossless conditions, they do not step-up or step-down the voltage. They are used to electrically isolate two circuits; protect the microphone from DC voltages (ie: phantom power); and to balance the mic signal.
Transformers are used in microphones for several reasons:
- To increase the voltage, and therefore the strength, of the mic signal.
- To convert the impedance of the mic signal to a usable level.
- To balance the mic signal at the output.
- To block DC voltage from entering the microphone circuitry.
Transformers can be found in the following microphone types:
- Moving-coil dynamic microphones.
- Passive ribbon microphones.
- Active ribbon microphones.
- True condenser microphones.
- Tube microphones.
Related article: What Are Microphone Transformers And What Is Their Role?
What Is A Transistor And What Is Its Role In A Microphone?
What is a transistor? A transistor is an active semiconductor device capable of amplifying or switching electronic signals and electrical power. Transistors basically work with a voltage/current in applied to one of the transistor terminals and controls the current through the another pair of terminals.
The transistors in microphones are typically FETs (field-effect transistors) or JFETs (junction-gate field effect transistors).
Note that I am not an electrical engineer and I do not fully understand these devices. I will explain them here in layman’s terms.
FETs and JFETs work with 3 terminals:
A simple diagram of a field-effect transistor with the gate (G), source (S), and drain (D) is pictured below:
By applying a voltage to the gate, we alter the conductivity between the drain and source. In this way, we can use a voltage at the gate to control the current out of the source and drain.
The input impedance at the gate is extremely high while the output impedance is much lower coming out of the FET/JFET.
When active mics are designed with transistors, the electrical signal from their capsules is applied to the gate of the FET/JFET. This AC voltage from the capsule then controls the flow of a stronger electrical signal with less impedance at the FET/JFET output.
This makes the FET/JFET an excellent impedance converter, which is its primary job in microphones.
The output impedance of a condenser capsule has very high impedance. Placing a transistor (with extremely high input impedance) immediately after the capsule will convert the impedance to a lower value before the signal gets severely degraded as it travels through the circuit.
The FET/JFET also acts as a type of amplifier. The high-impedance low-level signal from the capsule acts only as a controller for a stronger output signal from the transistor. A relatively weak signal at the FET/JFET input controls a stronger mic signal at the output.
Transistors are used in microphones for several reasons:
- To lower the high-impedance of the mic signal to a usable level.
- To increase the voltage, and therefore amplify the mic signal.
Transistors can be found in the following microphone types:
- Active ribbon microphones.
- Electret condenser microphones.
- True condenser microphones.
- Lavalier/miniature microphones.
Do All Microphones Have Transformers And Transistors?
The quick answer is no. Not all microphones have transformers and transistors.
Some microphones have neither, some have both, and others have only one.
Although there are some standard microphone designs that include transformers and/or transistors, it usually depends on the specific designs of the specific microphone in question.
Let’s quickly list out the microphone designs that always either have or don’t have transformers or transistors:
- Passive microphones never have transistors (moving-coil dynamic and passive ribbon mics).
- Tube microphones never have transistors (vacuum tubes and transistors have the same function in microphones).
- Passive ribbon microphones always have transformers (I haven’t found one that doesn’t).
- Lavalier/miniature microphones do not have transformers (transformers are too big to physically fit into the design).
- Electret condensers never have transformers (I haven’t found one that does).
Other than the absolutes listed above, the question of whether a mic has a transformer, a transistor, neither, or both is specific to that microphone.
Let’s go over some common microphone types and some specific microphone examples that have transformers and/or transistors in their design.
Once again, the microphone types we’ll be discussing are:
- Moving-Coil Dynamic Microphones.
- Passive Ribbon Dynamic Microphones.
- Active Ribbon Dynamic Microphones.
- Electret Condenser Microphones.
- “True” Condenser Microphones.
- Tube Condenser Microphones.
- Lavalier/Miniature Microphones.
Do Moving-Coil Dynamic Microphones Have Transformers?
Some moving-coil dynamic microphones do have output transformers and others do not.
Moving-coil dynamic microphones often have step-up transformers at their outputs.
The electrical signal outputted from a moving-coil cartridge/diaphragm often has very low voltage and impedance. A step-up transformer effectively boosts this AC voltage to a mic level output signal without boosting the impedance to unusable levels.
Additionally, the step-up transformer will effectively block any potential DC voltage at the secondary winding from passing through to the primary winding. This protects the moving-coil cartridge and passive circuitry from the potentially harmful phantom power.
Good output transformers cost significant money when discussing relatively inexpensive moving-coil dynamic mics.
Conversely, inexpensive/cheap transformers make for poor performance in microphones. Cheap transformers are noisy and produce non-linear distortion at relatively low signal levels.
Therefore, designing a moving-coil microphone with a good transformer will increase its price point.
Designing a dynamic microphone with a decent output transformer will lower the price point but result in significant colouration to the sound and lower distortion levels.
When it comes to cheap transformers, it’s better to not put a transformer in the moving-coil dynamic mic at all. This will make for a cheap mic with a better sound.
The cons of a transformerless mic are that it is not necessarily protected from DC voltages like phantom power and the output may be weaker without any step-up in voltage.
The legendary Shure SM57 is an example of a moving-coil dynamic mic with a transformer.
Shure SM57 Transformer: Shure 51A303
- Sensitivity: -56.0 dBV/Pa (1.6 mV)
- Output impedance: 150 Ω (310 Ω actual)
Shure is featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
The output transformer of the Shure SM57 is partly responsible for its notable presence boost (sometimes referred to as its “honk”).
A common mod of the Shure SM57 is to remove the transformer completely from the circuit and simply tie the two leads from the moving-coil to pins 2 and 3. This is known as the “tape-op mod.”
Removing the transformer from the SM57 does a few things:
- Reduces the output levels (no more voltage step-up).
- Increases low-end (the relatively low-cost transformer reduces low-end).
- Lowers the output impedance (no more impedance step-up).
Another common mod for the Shure SM57 is replacing the inexpensive Shure 51A303 transformer with a higher-end TAB Funkenwerk AMI T58 transformer.
The AMI T58 mod enhances the sound of the SM57, making it noticeably clearer and warmer.
The Electro-Voice RE320 is an example of a moving-coil dynamic mic that does not have a transformer.
- Sensitivity: 2.5 mV/pascal
- Output impedance: 150 Ω
Electro-Voice is also featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
How are transformerless dynamic microphone signals balanced?
The leads taken from each end of the moving-coil diaphragm/cartridge are inherently balanced so long as they aren’t connected to ground.
By connecting the leads of the moving-coil to pins 2 and 3 and adding a ground to pin 1 (connected to the microphone chassis), a balanced signal can be achieved.
Do Moving-Coil Dynamic Microphones Have Transistors?
No, moving-coil microphones do not have transistors.
For more information on moving-coil dynamic microphones, check out my article The Complete Guide To Moving-Coil Dynamic Microphones.
Do Passive Ribbon Dynamic Microphones Have Transformers?
All passive ribbon dynamic mics have transformers.
Passive ribbon dynamic mic diaphragms/elements typically output electrical signals even lower in signal than their moving-coil counterparts. They benefit greatly from amplification characteristics of a step-up transformer coupled output.
The low-voltage low-impedance signal from the ribbon element gets stepped-up by the transformer. It effectively gets boosted to a mic level signal with a low impedance that will allow it to work with professional preamps and other gear.
It’s also important to note that ribbon diaphragms are very fragile. Without a transformer to block DC voltage, any instance of phantom power would likely fry the ribbon. For this reason, passive ribbons are designed with output transformers.
The Royer R-121 is but one example of a passive ribbon dynamic mic. Like all passive ribbons mics, it has a transformer.
Royer R-121 Transformer: Custom
- Sensitivity: -47 dBV/Pa
- Output impedance: 300 Ω @ 1K (nominal)
Royer is also featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
Do Passive Ribbon Dynamic Microphones Have Transistors?
No, passive ribbon microphones never have transistors.
For more information on ribbon dynamic microphones, check out my article The Complete Guide To Ribbon Microphones (With Mic Examples).
Do Active Ribbon Dynamic Microphones Have Transformers?
Active ribbon microphones have transformers, but they’re not our typical output transformers. Rather, the step-up transformers in these active mics are put immediately after the ribbon element. Their output signals are then run through the active circuitries and transistors before the mic signal is outputted.
In active ribbon design, the transformer does much of the heavy lifting in terms of signal amplification.
As the step-up transformer increases the voltage, it also increases the impedance of the signal.
Theoretically, the step-up voltage ratio is equal to the turns ratio between the primary and secondary winding. The impedance ratio, however, is equal to the square of the turns ratio.
As an example, let’s say we had a 1:12 transformer (not an uncommon ratio) at the ribbon output. This step-up transformer would boost the voltage 12x (and drop the current 1/12x) while increasing the impedance by 122x or 144x.
So the transformers in active ribbon mics yield a relatively high voltage mic level signal but the impedance is too high for practical use with other professional equipment. This is where the active circuitry comes into play.
The active “amplifier circuit” acts more so as an impedance converter, dropping the high impedance of the transformer’s stepped-up output signal down to usable levels.
The transistors (FET or JFET) in active ribbon mics are centrepieces of this active circuitry. The high-impedance signal out of the transformer is effectively converted to a low-impedance signal with relatively small gain changes (if any).
Royer R-122 is actually the world’s first active ribbon. The second generation Royer R-122 MKII is an excellent example of an active ribbon mic with a transformer that is on the market today.
Royer R-122 Transformer: Custom Toroidal
- Sensitivity: -36 dBV/Pa
- Output impedance: 200 Ω @ 1K (nominal)
Although the R-122 MKII contains an active “amplification circuit,” it’s the transformer that does most of the heavy lifting as far as signal gain is concerned.
The active electronics and balanced field-effect transistors act primarily to provide a perfect load on the ribbon element at all times and to convert the impedance of the ribbon transformer output signal before it reaches the output.
Let’s take a look at the Royer R-122V, the tube version of the R-122.
The R-122V actually has 2 transformers in its design: the step-up transformer at the ribbon output and a step-down Jensen transformer at the output (found within the mic’s external power supply).
The step-up transformer, like most active ribbon mic transformers, is put in between the ribbon output and the active impedance converter (in this case, the JAN 5840W vacuum tube).
The step-up transformer essentially amplifies the ribbon’s output voltage. The increase in impedance inherent in a step-up transformer is converted by the tube and then further reduced by the Jensen output step-down transformer.
Like most tube microphones, the R-122V is designed with a step-down transformer at its output. This transformer helps drop the impedance to usable levels while also balancing the audio signal from the tube at the microphone output.
Do Active Ribbon Dynamic Microphones Have Transistors?
Active ribbon mics will have transistors (FETs or JFETs) unless they use tubes.
As we’ve just discussed, the transistors and active circuitries of active ribbon mics typically come after the transformer.
After the transformer boosts the ribbon’s output signal and the impedance of that signal, the transistor circuitry must act as an impedance converter. It’s essential to have a transistor circuit in order to bring the impedance down to a usable level without overly affecting the sound or voltage level of the signal.
The AEA A440 is one of the many active FET ribbon microphones.
- Sensitivity: 30 mV/Pa (-33.5 dBV)
- Output impedance: 92 Ω
AEA is featured in My New Microphone’s Top 11 Best Microphone Brands You’ve Likely Never Heard Of.
Once again, here’s the Royer R-122V. It is an example of an active ribbon microphone that uses tube electronics rather than a transistor circuit.
- Sensitivity: -36 dBV
- Output impedance: 200 Ω
The vacuum tube in the R-122V provides impedance conversion and minor amounts of “amplification.”
Like the transistor circuits in non-tube active ribbon mics, the vacuum tube of the R-122V is put after the ribbon output’s step-up transformer. The tube acts to bring down the impedance of the stepped-up signal.
Unlike the transistor-based active ribbon mics, tube ribbon mics have output transformers as well. These output transformers actually step-down the voltage and impedance to professional levels at the microphone output.
Do Electret Condenser Microphones Have Transformers?
I have not found any electret condenser microphones that have transformers.
Amplification, impedance conversion, and balancing all take place within the solid-state circuit boards of electret mics.
Do Electret Condenser Microphones Have Transistors?
Yes, electret condenser microphones require transistors (FETs or JFETs) to drop the impedance and amplify the signals from the electret capsules.
The output from a condenser capsule (electret or not) has extremely high impedance. Electret microphones rely on their transistors to effectively convert this impedance to a usable level.
The Rode NT1-A is a popular example of a professional-grade electret microphone.
- Sensitivity: 31.9dBV/Pa (25.00mV @ 94 dB SPL)
- Output impedance: 100 Ω
Rode is featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
For more information on electret condenser microphones, check out my article The Complete Guide To Electret Condenser Microphones.
Do “True” Condenser Microphones Have Transformers?
Some true FET condensers have output transformers while others do not. Many older models have output transformers while newer models are designed with or without transformers.
The term “true condenser” essentially means that the condenser mic is non-tube and non-electret. In other words, “true condensers” have externally polarized capsules and require transistors (rather than vacuum tubes) to convert the high-impedance signals from the mic capsule into low-impedance signals at the output.
The output transformers of true condenser microphones are step-down transformers.
The transistors (FET/JFETs) of condenser microphones do an excellent job at lowering the capsule’s output signal impedance while essentially amplifying it. The output transformer further reduces the signal impedance so the mic’s output can be used effectively with professional gear.
The Neumann KM 84 (discontinued) is an excellent example of an older FET microphone with an output transformer.
Neumann KM 84 transformer: Haufe BV107
- Sensitivity: 10 mV/Pa
- Output impedance: 150 Ω
Note that the KM 84 has been replaced by the newer KM 184, which does not have an output transformer.
Neumann is also featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
The NEAT King Bee is an excellent example of a modern microphone with an output transformer.
Neat King Bee transformer: Custom
Transistor: 2SK170 JFET
- Sensitivity: 26.0mV/Pa
- Output impedance: 150 Ω
Neat Microphones is featured in My New Microphone’s Top 11 Best Microphone Brands You’ve Likely Never Heard Of.
The Neumann TLM 103 (TLM stands for Transformer-Less Microphone) is an excellent example of a modern “true” microphone without a transformer.
- Sensitivity: 23 mV/Pa
- Output impedance: 50 Ω
The TLM 103 relies completely on its active FET and op-amp based output circuitry to drop the impedance and boost the voltage of its capsule’s output signal.
According to Neumann, their active circuit has several advantages over output transformers. These advantages include reduced noise and harmonic distortion; cleaner (less coloured) amplification; and higher current output.
Do “True” Condenser Microphones Have Transistors?
Yes, all true FET condenser microphones have transistors. These non-tube microphones require active transistor-based circuits to convert the high impedance of their capsule outputs to lower impedances that allow the signals to travel through any significant length of cable.
The NEAT King Bee is a cool example of a “true condenser” microphone.
Transistor: 2SK170 JFET
Neat King Bee transformer: Custom
- Sensitivity: 26.0mV/Pa
- Output impedance: 150 Ω
Do Tube Condenser Microphones Have Transformers?
Yes, most tube condenser microphones have output transformers.
Vacuum tubes essentially do the same job as FETs and JFETs. They convert impedance and provide “amplification” to a condenser capsule’s output signal. Really, they provide their own electrical signal that is controlled by the output signal of the condenser capsule’s output.
So the vacuum tubes in tube mics provide some impedance conversion and output higher voltages than the capsules are capable of. However, they do not balance the capsule’s audio signal, nor do they typically drop the impedance low enough.
For those reasons, step-down transformers are commonly designed into tube condenser microphones outputs.
The step-down transformers act to drop the impedance to usable levels while also balancing the audio signal at the microphone output.
An excellent example of a modern tube condenser mic with an output transformer is the Sony C-800G.
Sony C-800G transformer: Custom
- Sensitivity (Uni): -32.0dB/Pa
- Sensitivity (Omni): -35.0dB/Pa
- Output impedance: 100 Ω
A modern examples of a transformerless tube condenser microphone is the Neumann M 150 Tube.
- Sensitivity: 20 mV/Pa
- Output impedance: 50 Ω
The Neumann M 150 Tube, like the aforementioned TLM 103, uses an op-amp based output circuitry (with transistors) to balance and convert the impedance of its output signal.
Do Tube Condenser Microphones Have Transistors?
Though transistors and vacuum tubes perform the same functions in active microphones (they both act as impedance converters and “amplifiers” of the capsule’s output signal), some tube mics will have transistors.
Originally, vacuum tubes were necessary in professional condenser microphones. The JFET was first patented by Heinrich Welker in 1945, but it wasn’t until 1965 that the first condenser microphone was built using FET circuitry rather than tube electronics (that mic was the Sony C-38 FET).
Since then, manufacturers have continued improving upon the transistor-based circuitries of active microphones.
Transistors have the potential to output a more technically perfect sound while vacuum tubes are said to have more “character.”
That being said, FETs and tubes both perform the same function and so microphones usually aren’t designed with both units.
However, there are always exceptions to the rules.
Let’s take another look at the Neumann M 150 Tube microphone, which utilizes a vacuum tube and transistors in its design.
- Sensitivity: 20 mV/Pa
- Output impedance: 50 Ω
The Neumann M 150 Tube uses a 6111 vacuum tube to boost its capsule level and to provide impedance conversion.
The unbalanced output of the 6111 is then passed through a transistor-based output circuit that balances the signal while further optimizing its impedance.
For more information on tube condenser microphones, check out my article The Complete In-Depth Guide To Tube Condenser Microphones.
Do Lavalier/Miniature Microphones Have Transformers?
No. Transformers are generally too big to fit inside small lavalier microphones.
Lavalier mics are typically electret condensers, and so their circuitries act to balance their audio signals and convert impedance. As for dynamic lavs (like the Shure SM11 CN that we’ll talk about shortly), the cartridge outputs a balanced signal and can be used as the mic’s output.
Do Lavalier/Miniature Microphones Have Transistors?
Because most lavalier microphones are electrets, they require transistors to bring down the impedance to a usable level at the mic output.
That being said, not all lavalier mics are electrets (or condensers for that matter) and so not all laveliers require an impedance-converting transistor circuit.
The Sennheiser MKE2 is an example of an electret condenser lavalier mic that requires a transistor.
- Sensitivity: 5 mV/Pa
- Output impedance: 1,000 Ω
Sennheiser is also featured in My New Microphone’s Top 11 Best Microphone Brands You Should Know And Use.
The Shure SM11 CN is an example of a dynamic lavalier microphones that does not have any transistors in its design.
- Sensitivity: -64 dBV/Pa (0.60 mV
- Output impedance: 150 Ω (200 Ω actual)
For more information on lavalier microphones, check out my article How And Where To Attach A Lavalier/Lapel Microphone.
What is an electret condenser microphone? An electret condenser mic has a permanently charged capsule. This is achieved by adding electret material to one of the plates of the condenser’s parallel-plate capacitor capsule. Electret condensers are still active, requiring electricity to power their transistors (impedance converter/ amplifier).
What is a tube condenser microphone? A tube condenser mic utilizes a vacuum tube (rather than a transistor) to amplify and adjust the impedance of the condenser capsule’s output signal. The output of a tube is still generally high impedance and so step-down transformers are often used at the output to optimize the mic output impedance.