Complete Guide To Microphone Preamplifier Specifications

If you're familiar with microphones, you'll know that they require preamplifiers to boost their relatively low-strength output signals to usable levels. Microphone preamps come in various shapes and sizes and are defined by a list of specifications.

What are microphone preamplifier specifications? Mic preamp specifications, shown on specifications/datasheets and product pages, are pieces of information that tell us the electrical and physical characteristics of the preamplifier and the features available for use within the mic preamp.

In this article, we'll describe each of these mic preamp specifications and what they mean to the overall functionality of the preamp in question. Note that some microphone preamplifiers are subject to different specs than others based on their functionality.

Related article: What Is A Microphone Preamplifier & Why Does A Mic Need One?

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Preamplifier Specifications

The role of a microphone preamplifier is fairly simple to understand: it boosts the mic level signal of the microphone to line level, allowing the mic signal to be effectively processed, recorded, and played back.

However, the actual electronics of the amplifier vary in complexity and can be defined by all sorts of specifications. This is especially true if the preamp unit offers additional functionality (PADs; EQ and filters; phantom power, etc.)

I will list all the potential specifications you may find on mic preamp datasheets, manuals and selling pages. Each spec will be described briefly with links to more in-depth articles when applicable. I will also add real-world examples of microphone preamplifiers that have the specifications mentioned.

To provide real-world examples of each specification, I've collected a series of datasheets/product pages from specific mic preamp manufacturers of various headphone types. The examples are listed below:

The included links will bring you to the bottom of this article, where each of the preamps is described in more detail, with all their specifications laid out as a reference.

Alternatively, you can skip to the section Preamplifier Examples For This Article by clicking the link.

Microphone preamplifier examples:

• Cloud Microphones CL-Z
• BAE 1073DMP Desktop
• Heritage Audio 1084
• Chandler REDD.47
• Warm Audio WA273-EQ

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List Of Preamplifier Specifications

• Description
• Features
• Circuit/Components
• Inputs
• Input Impedance
• Equivalent Input Noise
• Noise
• Inserts
• Gain (voltage and dB)
• Outputs
• Output Impedance
• Maximum Output Level
• Total Harmonic Distortion
• Common Mode Rejection Ratio
• Controls
  • Gain Control (Voltage gain – Fine gain – Total gain)
  • PAD
  • Phantom Power
  • Tone Button
  • Polarity Switch
  • Output Control
  • Rumble Filter
  • EQ Controls
• Indicators
• Power Supply & Requirements/Consumption
• Mounting
• Weight
• Dimensions
• Packaging

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Description

This “specification” is typically not in the technical specifications section of the mic preamp specs sheet. Rather, it's a paragraph (or several) written by the manufacturer (typically by the marketing team rather than the engineering team) to describe the particular unit.

The description includes information the manufacturer thought important to include about the microphone preamplifier (applications, circuits, amplifier class, EQ, etc.).

Examples

Cloud Microphones CL-Z

Compact, single-input solution for common audio problems in the field and the studio involving low-output passive microphones, including ribbons.

Chandler REDD.47

Chandler Limited's REDD.47 Mic Amplifier is a recreation of the original valve line amplifiers used in Abbey Road Studios' heralded and rare EMI REDD.51 recording consoles circa 1959-1968.

Warm Audio WA273-EQ

• Description: Dual Channel, Class A, ’73-Style British Microphone Preamp With EQ

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Features

The features section of a mic preamp specs sheets lists out important bullet points about the microphone preamplifier.

This “spec” will include several other specifications that the manufacturer believes should be known.

Examples

BAE 1073DMP Desktop

Features

• Built-in PSU for extra portability
• DI in and DI through
• 48v for phantom power
• Solid steel chassis
• Same hand-wired modular design that BAE is known for

Heritage Audio 1084

Features:

• Input gain switch:
  • 5dB steps from 20 to 80 in MIC mode
  • -10 to 10 dB in LINE mode
• High shelf: Fixed at 12 kHz
• Hi Q: Switches the Q of the mid band
• Mid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHz
• Bass shelf: 220, 110, 60 and 35 Hz
• High pass filter: 300, 260, 80, 50 Hz
• Lo pass filter: 6, 8, 10, 14, 18 kHz
• EQL: Turns equalizer ON
• Phase: Flips phase 180º

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Circuit/Components

The circuit/components specification will tell us about any special components used in the microphone preamp design.

For example, the vacuum tubes used in tube preamps are of great importance. The quality of the tube(s) is a major factor in the quality of the mic pre, and it's important to note the tube used in case of replacement.

Output transformers are also important for tube preamps and some solid-state mic preamps as well. The quality of the transformer will also directly affect the quality of the sound.

In addition to tubes and transformers, this specification can tell us how the circuits are constructed and other specific elements that are important to the functionality of the amp.

Examples

Chandler REDD.47

• Circuit: Tube (EF86, E88CC)
• Connections: Transformer balanced I/O (custom wound)

Warm Audio WA273-EQ

Components:

• UK Made Carnhill Transformers
• UK Made – Blore Edwards EQ Dual-Concentric Switch Potentiometers
• Hand Wired, Hand Assembled
• Fully Discrete

Related article: Do Microphone Preamplifiers Improve Sound/Audio Quality?

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Inputs

The inputs specification refers to, well, the inputs of the mic pre.

Microphones generally connect via balanced 3-pin XLR cables, so the overwhelming majority of microphone preamplifier inputs will be female 3-pin XLR.

That being said, some microphone preamps double as instrument preamps and even line amps. In these cases, the additional inputs will be stated in this spec.

Otherwise, the number of inputs will be listed on the microphone preamp (not all microphone preamplifiers have only one input).

Examples

Cloud Microphones CL-Z

I/O:

• 1x XLR input

Chandler REDD.47

Connections:

• Inputs: Mic/Line XLR (pin 2 hot), D/I (1/4”)
• Transformer balanced I/O (custom wound)

Warm Audio WA273-EQ

Inputs:

• XLR Mic Inputs (Front & Back)
• Line Level TRS Input
• Direct In, Instrument Input

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Input Impedance

The input impedance of the mic preamp is an important specification since it is the effective load that the microphone (or another source device) must drive.

In general, the input (load) impedance of a mic input should be about 10 times the microphone's output impedance. This is referred to as impedance bridging and yields the best voltage/signal transfer between the mic and mic preamp.

In the case that the load impedance is lower, the signal transfer may suffer. This is particularly true in the low-end and resonant frequencies of the microphone. Altering the input impedance of a microphone preamplifier may actually change the sound of the microphone.

To learn more about microphone impedance, check out my article Microphone Impedance: What Is It And Why Is It Important?

Examples

Cloud Microphones CL-Z

Input Impedance: 150 ohms to 15 kOhms

BAE 1073DMP Desktop

• Mic Pre Input Impedance: ≅1200 ohms
• DI Input Impedance: ≅150k ohms

Heritage Audio 1084

• Microphone input impedance:
  • HI: 1200 Ohm minimum
  • LO: 300 Ohm minimum
  • Higher gain positions gradually have greater impedances, optimum for low gain ribbon mics. Input is transformer balanced and floating
• Line input impedance: 10KOhms bridging, transformer balanced and floating

AEA TRP2

• Input Impedance: 63K Ohms
• Input Impedance (P48 Engaged): 10K Ohms

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Equivalent Input Noise

The equivalent input noise (otherwise known as self-noise) is the inherent noise produced by the mic preamplifier. This noise is added to the audio signal as it is amplified through the preamp.

Preamps are active devices that apply gain to the inputted mic signal. With powered/active components, noise is inevitable. Gain devices are particularly prone to added noise.

The actual EIN specification is typically measured in negative decibels A-weighted (which are calibrated to human hearing). The data tells us how much lower the added noise will be compared to the output signal of the mic preamp.

Examples

BAE 1073DMP Desktop

Equivalent Input Noise: -110 dBu; Unweighted 300kHz Bandwidth

Heritage Audio 1084

• Noise: Less than -100dBu

AEA TRP2

• EIN: <-130dBu A-weighted, 150 Ohm resistive source

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Noise

Noise rating is similar to equivalent input noise except that it's absolute. Rather than comparing the noise to the output signal, it's compared to the threshold of no signal level.

Examples

AEA TRP2

• Noise figure, rms A-weighted: <2dB
• Noise figure, rms unweighted: <3dB, 20 kHz LPF bandwidth

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Insert

An insert is an output to input loop-type circuit that allows other processors (compressors, equalizers, etc.) to be “inserted” into the preamplifier.

These inserts are post gain but pre output. They essentially allow us to include a completely new circuit (or multiple circuits) within the microphone preamplifier.

The insert specification generally refers to the output and input connections that allow for the insert.

Examples

Warm Audio WA273-EQ

Inserts:

• TS Send/Receive Insert Jacks

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Gain

Gain is defined as the ratio of the output signal level to the input signal level. Generally, this is measured in voltage since audio signal strength is typically calculated in volts.

The actual gain controls of a mic preamp are nearly always set in decibels, which is a logarithmic scale rather than a linear scale. These decibel ratings make it easier to adjust preamp levels relative to other line audio signal levels that are most all also measured in decibels (either dBV or dBu).

The gain specification, then, will generally be listed as a dB rating. Depending on the preamp, the gain could be stepped (switching between discrete values) or continuously variable (fine adjustments up to a certain maximum level of gain).

Note that more gain typically means more noise. Some preamps will begin to distort and get noisy. This is often the case with driving dynamic microphones with low-gain preamps.

To learn more about gain and how it affects microphones, check out my article What Is Microphone Gain And How Does It Affect Mic Signals?

Examples

Cloud Microphones CL-Z

• Gain: +12 dB or +25 dB increase

BAE 1073DMP Desktop

• Gain Voltage: 0 to 33.4 Volts
• Gain dB: 0 to 71 dB

Heritage Audio 1084

Maximum Gain: Slightly greater than 80dB

Chandler REDD.47

• Voltage gain: Stepped 16-52db
• Fine gain: Stepped ±5db
• Total gain: +57db

Warm Audio WA273-EQ

• Gain: 80 dB of Gain – Resistor Stepped Gain Switch

AEA TRP2

• Gain at 1 kHz: 85dB of gain at 1 kHz, balanced-in to balanced-out in Microphone Input mode
• Mic Gain Control: Twelve-position switch provides from +7dB to +63dB of gain for the preamplifier circuit, as measured between the inputs and the before the output line driver.

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Outputs

The outputs specification lists the output connection of the microphone preamplifier (typically XLR), the number of outputs, and any interesting information about the output connections.

Examples

Cloud Microphones CL-Z

I/O:

• 1x XLR output

Chandler REDD.47

• Output: XLR (pin 2 hot)
  • Transformer balanced I/O (custom wound)
• Output control: variable

Warm Audio WA273-EQ

Outputs:

• XLR & TRS Line Level Outputs
• Output Control: Level

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Output Impedance

The output impedance of a microphone preamplifier is sometimes listed.

This specification is important since it tells us the source impedance of the transfer circuit to what device the amplifier is connected to (which would be the load).

Again, the source impedance should be at least 10 times less than the load impedance for decent signal/voltage transfer. Since the microphone preamplifier is designed to output line level signals, its output impedance should be in the range to effectively drive a connected line level input.

Examples

BAE 1073DMP Desktop

Output Impedance: 65 ohms

Heritage Audio 1084

Output impedance: Less than 75 Ohms, transformer balanced and floating, to drive a load of 600 Ohms

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Maximum Output Level

The maximum output level of a microphone preamp tells us how much the preamplifier is capable of outputting. Like most line level signal strength measurements, this spec is defined as a voltage or, more likely, as decibels relative to a voltage (dBu or dBV).

Again, because voltage transfer is dependent on the load impedance of the connected device, the max output level is generally tested and defined into a specified load impedance.

Exceeding the maximum output level will put the output into distortion. Note that, except for the situation that would have audio transients on high preamp gain settings, the maximum output level is rarely approached.

Examples

BAE 1073DMP Desktop

Maximum Output Level: +27.4 dBu @ 600Ω

Heritage Audio 1084

Maximum output: Greater than +26dBu into 600 Ohms

AEA TRP2

• XLR output maximum level into 600Ω load: +28 dBu, balanced; 0 dBu = 0.7746 V rms

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Total Harmonic Distortion

Total harmonic distortion aims to tell us the amount of distortion or “colouration” a microphone preamplifier will add to the sound.

Amplifiers add gain to an input signal to increase its level at the output. Applying gain, however clean the gain is, has the side effect of introducing distortion.

THD is a measurement of the harmonic distortion present in a signal. It is defined as the ratio of the sum of the powers of all harmonic components to the power of the fundamental frequency.

It is calculated with a simple sine wave (typically 1 kHz) and is stated as a percentage.

So specific testing circumstances must be used to calculate THD values for a preamp. It's important for the manufacturer to include these parameters.

Note that the THD specification, by itself, is inherent to the preamplifier.

Examples

Heritage Audio 1084

• THD: Less than 0.025% at 1Khz, Less than 0.05% at 100Hz

AEA TRP2

• THD: <0.02% at 1 kHz

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Common Mode Rejection Ratio

Microphones will typically output balanced audio signals via an XLR cable. Balanced signals are transferred as follows:

• Pin 1: common ground
• Pin 2: positive polarity (hot) signal
• Pin 3: negative polarity (cold) signal

The same audio signal is carried on pins 2 and 3 except in reverse phase.

The microphone preamp input is also balanced since it is designed to accept mic signals. Inside this input is a differential amplifier that effectively sums up differences between pins 2 and 3 (doubling the amplitude of the original signal). At the same time, the differential amp cancels out any noise/interference that is common to pins 2 and 3.

The amount the preamp can eliminate this common-mode noise is referred to as common-mode rejection and is typically defined in decibels. The rating tells us how much the interference noise of the input signal will be reduced.

Examples

BAE 1073DMP Desktop

Common Mode Rejection Ratio: 100dB min @ 60Hz

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Controls

Preamps have controls for their circuits.

Pretty much every preamp has a gain control that allows the user to adjust the gain applied to the signal manually. Most preamps will also have a phantom power switch (which is a form of control).

However, a microphone preamplifier may have plenty of other potential controls, especially if it has a built-in EQ.

Examples

Cloud Microphones CL-Z

• Input Impedance: 150 ohms to 15 kOhms
• Gain: +12 dB or +25 dB increase

BAE 1073DMP Desktop

• Gain Voltage: 0 to 33.4 Volts
• Gain dB: 0 to 71 dB

Heritage Audio 1084

Features:

• Input gain switch:
  • 5dB steps from 20 to 80 in MIC mode
  • -10 to 10 dB in LINE mode
• High shelf: Fixed at 12 kHz
• Hi Q: Switches the Q of the mid band
• Mid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHz
• Bass shelf: 220, 110, 60 and 35 Hz
• High pass filter: 300, 260, 80, 50 Hz
• Lo pass filter: 6, 8, 10, 14, 18 kHz
• EQL: Turns equalizer ON
• Phase: Flips phase 180º

Chandler REDD.47

Controls:

• Voltage gain: Stepped 16-52db
• Fine gain: Stepped ±5db
• Total gain: +57db
• Output control: variable
• Rumble filter: Inductor based, switchable (30,45,60,70,90,110,130,180hz)
• PAD: 20db, switchable
• Phase: 0/180º, switchable
• Phantom Power: +48v, switchable

Warm Audio WA273-EQ

Controls:

• Tone Button: Changes Input Transformer Impedance For Varying Tone
• Polarity Switch: In-Phase/Flipped-Phase
• 48V Phantom Power: On/Off
• Low Band Boost/Cut: 35, 60, 110, 220 Hz
• Mid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 Hz
• High Band Boost/Cut: 10, 12, 16 kHz
• 4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 Hz
• Output Control: Level
• EQ: Dual-Concentric Switch Potentiometers
• Gain: Resistor Stepped Gain Switch

AEA TRP2

• Mic Gain Control: Twelve-position switch provides from +7bD to +63dB of gain for the preamplifier circuit, as measured between the inputs and the before the output line driver.
• Output Level Potentiometer: 22dB
• Low-Cut Filter: 12dB per octave from 100 Hz

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Gain Control (Voltage gain – Fine gain – Total gain)

The gain control tells us how much gain is available and how we can control it (stepped and/or continuously variable).

Examples

Cloud Microphones CL-Z

• Gain: +12 dB or +25 dB increase

BAE 1073DMP Desktop

• Gain Voltage: 0 to 33.4 Volts
• Gain dB: 0 to 71 dB

Heritage Audio 1084

Input gain switch:

• 5dB steps from 20 to 80 in MIC mode
• -10 to 10 dB in LINE mode

Chandler REDD.47

• Controls:
  • Voltage gain: Stepped 16-52db
  • Fine gain: Stepped ±5db
  • Total gain: +57db

Warm Audio WA273-EQ

• Gain: 80 dB of Gain – Resistor Stepped Gain Switch

AEA TRP2

• Mic Gain Control: Twelve-position switch provides from +7bD to +63dB of gain for the preamplifier circuit, as measured between the inputs and the before the output line driver.

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PAD

A pad is a passive attenuation device. When engaged, a pad will attenuate the output of the microphone preamplifier by a certain amount of decibels.

Pads are useful to keep the output of the preamp from getting overdriven and/or to allow us to drive more gain (and saturation/colouration) to the signal.

For more information on pads and how they affect microphones, check out my article What Is A Microphone Attenuation Pad And What Does It Do?

Examples

Chandler REDD.47

• PAD: 20db, switchable

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Phantom Power

Phantom power is essential to power many of the condenser microphones on the market and even some active ribbon microphones. It is +48V DC on pins 2 and 3.

To learn exactly how phantom power works, check out my article What Is Phantom Power And How Does It Work With Microphones?

Examples

BAE 1073DMP Desktop

• Features:
  • 48v for phantom power

Chandler REDD.47

Phantom Power: +48v, switchable

Warm Audio WA273-EQ

48V Phantom Power: On/Off

AEA TRP2

• Input Impedance: 63K Ohms
• Input Impedance (P48 Engaged): 10K Ohms

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Tone Button

A tone button or knob is included on some microphone preamps that will alter the preamp's circuitry to alter the tonal characteristics of the output signal.

Examples

Warm Audio WA273-EQ

Tone Button: Changes Input Transformer Impedance For Varying Tone

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Polarity Switch

Audio signals are AC. A polarity switch allows the user to flip the positive and negative polarity of the audio signal.

Flipping polarity/phase can help to ameliorate phase issues in multi-track recording situations that have microphones in close proximity.

For more info on audio polarity/phase and microphones, read my article Microphone Polarity & Phase: How They Affect Mic Signals.

Examples

Heritage Audio 1084

• Features:
  • Phase: Flips phase 180º

Chandler REDD.47

• Controls:
  • Phase: 0/180º, switchable

Warm Audio WA273-EQ

• Controls:
  • Polarity Switch: In-Phase/Flipped-Phase

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Output Control

Some preamplifiers will have an additional output control. This is typically a volume potentiometer at the back end of the preamp to help adjust the output without altering the gain characteristics of the main gain stage.

The output control can act similarly to a pad and is typically put after the inserts in the preamps that have insert ports.

Examples

Chandler REDD.47

• Controls:
  • Output control: variable

Warm Audio WA273-EQ

• Controls:
  • Output control: level

AEA TRP2

• Output Level Potentiometer: 22dB

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EQ Controls

Some preamplifiers have EQ controls to help shape the signal.

These EQs feature filters, shelves, and other boosts and cuts.

To learn more about high-shelf and low-shelf filters, check out my article Audio Shelving EQ: What Are Low Shelf & High Shelf Filters?

Examples

Heritage Audio 1084

• High shelf: Fixed at 12 kHz
• Hi Q: Switches the Q of the mid band
• Mid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHz
• Bass shelf: 220, 110, 60 and 35 Hz
• High pass filter: 300, 260, 80, 50 Hz
• Lo pass filter: 6, 8, 10, 14, 18 kHz
• EQL: Turns equalizer ON

Chandler REDD.47

Rumble filter: Inductor based, switchable (30,45,60,70,90,110,130,180hz)

Warm Audio WA273-EQ

• Controls:
  • Tone Button: Changes Input Transformer Impedance For Varying Tone
  • Low Band Boost/Cut: 35, 60, 110, 220 Hz
  • Mid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 Hz
  • High Band Boost/Cut: 10, 12, 16 kHz
  • 4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 Hz
  • EQ: Dual-Concentric Switch Potentiometers

AEA TRP2

• Low-Cut Filter: 12dB per octave from 100 Hz

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Indicators

Indicators are typically lights that either flash/flicker or light up to indicate occurrences and states of performance of the microphone preamplifier.

These indicators could tell us any of the following:

• Power on
• Standby
• Signal
• Limit
• Phantom power engaged
• Phase flipped

Examples

Warm Audio WA273-EQ

Indicators:

• LED Level Indication

AEA TRP2

• LED signal level indicators:
  • The green LED snaps on at -20 dBy to indicate the presence of signal;
  • The yellow LED snaps on at 0 dBu;
  • The red LED snaps on at +24dBu to warn of approaching signal overload

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Power Supply & Requirements/Consumption

These specifications will either tell us the compatible power mains for proper preamplifier functioning.

Alternatively, they could tell us the precise voltage the preamp requires from its power supply/converter and how current the preamplifier is likely to draw from the power supply.

For more info on power and preamplifiers, please consider reading my article Why Do Audio Amplifiers & Preamplifiers Need Power To Work?

Examples

BAE 1073DMP Desktop

Power Requirements: 115/230 VAC, 28W

Heritage Audio 1084

Power consumption: Less than 110 mA @24VDC

Chandler REDD.47

• Power: Internal power supply

Warm Audio WA273-EQ

• Power: Internal IEC 115V/230V Power Inlet

AEA TRP2

• Power Supply Weight: 13 oz (0.37 kg)
• Power Supply Length: 7 feet 8.5 inches (2.3 m)
  • Power supply length may be supplemented with longer IEC cable

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Mounting

Many preamplifiers are rack-mountable into certain cases. The mounting specification will tell us how the preamplifier ought to be mounted, if at all.

Examples

Warm Audio WA273-EQ

• Mounting: 19″ Rackmountable

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Weight

This refers to the weight of the preamp and the weight of any included accessories.

Examples

BAE 1073DMP Desktop

• Weight: 7.3 LBS/3.31 KG

AEA TRP2

• Weight: 2.2lbs (1 kg)
• Power Supply Weight: 13 oz (0.37 kg)

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Dimensions

The dimensions spec refers to the overall length, width and depth of the mic preamp unit.

Examples

BAE 1073DMP Desktop

Dimensions (Inches): 5.3W x 4L x 11D

AEA TRP2

• Dimensions:
  • Half-rack wide, rack unit high (measured with knobs):
    8.5″ w, 8″ d, 1.8″ h (21.59 cm x 20.32 cm x 4.6 cm)

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Packaging

Packaging specifications will generally tell us the weight and dimensions of the box that the mic pre ships in.

Examples

Cloud Microphones CL-Z

Packing info:

• Package Weight: 1.25 lb
• Box Dimensions (LxWxH): 6.693 x 4.331 x 2.835″

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Preamplifier Examples For This Article

I've included plenty of microphone preamplifier examples in this article to showcase real-world specifications in the above descriptions.

Within these examples, there's a tube mic preamp, a ribbon mic preamp, a mic preamp with EQ, and many more to get a full variety of what is available on the market.

Each microphone preamplifier mentioned in this article is defined in more detail below, with a full list of its manufacturer-published specifications for reference.

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Cloud Microphones CL-Z

The Cloud Microphones CL-Z is a “mic activator” preamplifier with Vari-Z (variable impedance) and Vari-HPF (variable high-pass filter) controls.

Link to check out the Cloud Microphone Cloudlifter Z specifications.

• I/O:
  • 1x XLR input
  • 1x XLR output
• Input Impedance: 150 ohms to 15 kOhms
• Gain: +12 dB or +25 dB increase
• Packing info:
  • Package Weight: 1.25 lb
  • Box Dimensions (LxWxH): 6.693 x 4.331 x 2.835″

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BAE 1073DMP Desktop

The BAE 1073DMP Desktop Mic Pre is the first portable 1073 microphone preamplifier. This preamp is based on the design of the legendary Neve 1073 preamp and even has the same preamp circuit and the same Carnhill transformers as the 1073 and 1084.

Link to check out the BAE 1073DMP specifications.

• Features
  • Built-in PSU for extra portability
  • DI in and DI through
  • 48v for phantom power
  • Solid steel chassis
  • Same hand-wired modular design that BAE is known for
• Frequency Response: 10Hz to -3dB at 55kHz
• Mic Pre Input Impedance: ≅1200 ohms
• DI Input Impedance: ≅150k ohms
• Output Impedance: 65 ohms
• Common Mode Rejection Ratio: 100dB min @ 60Hz
• Maximum Output Level: +27.4 dBu @ 600Ω
• Power Requirements: 115/230 VAC, 28W
• Gain Voltage: 0 to 33.4 Volts
• Gain dB: 0 to 71 dB
• Equivalent Input Noise: -110 dBu; Unweighted 300kHz Bandwidth
• Weight: 7.3 LBS/3.31 KG
• Dimensions (Inches): 5.3W x 4L x 11D

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Heritage Audio 1084

The Heritage Audio 1084 is a Class-A mic preamp/EQ featuring custom polystyrene and polypropylene film tone capacitors. It provides up to 80 dB of gain and is designed to fit in the input module slots of vintage 80 Series sound mixing consoles. This pre/EQ can also be fitted into the Heritage Audio Frame 8 and Rack 2 powered enclosures.

Link to check out the specifications of the Heritage Audio 1084 preamp.

• Features:
  • Input gain switch:
    • 5dB steps from 20 to 80 in MIC mode
    • -10 to 10 dB in LINE mode
  • High shelf: Fixed at 12 kHz
  • Hi Q: Switches the Q of the mid band
  • Mid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHz
  • Bass shelf: 220, 110, 60 and 35 Hz
  • High pass filter: 300, 260, 80, 50 Hz
  • Lo pass filter: 6, 8, 10, 14, 18 kHz
  • EQL: Turns equalizer ON
  • Phase: Flips phase 180º
• Microphone input impedance:
  • HI: 1200 Ohm minimum
  • LO: 300 Ohm minimum
  • Higher gain positions gradually have greater impedances, optimum for low gain ribbon mics. Input is transformer balanced and floating
• Line input impedance: 10KOhms bridging, transformer balanced and floating
• Output impedance: Less than 75 Ohms, transformer balanced and floating, to drive a load of 600 Ohms
• Maximum output: Greater than +26dBu into 600 Ohms
• THD: Less than 0.025% at 1Khz, Less than 0.05% at 100Hz
• Frequency response: 20Hz (+0.3dB) to 20Khz (-0.2dB)
• Maximum Gain: Slightly greater than 80dB
• Noise: Less than -100dBu
• Power consumption: Less than 110 mA @24VDC

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Chandler REDD.47

The Chandler REDD.47 is a single-channel tube preamplifier for microphones. Note that the preamp itself is a tube amp and it is not only suited for tube microphones. The tube circuitry gives this preamp more character at the cost of being a bit heavier and pricier.

Link to the Chandler REDD.47 product page.

• Channels: Mono
• Circuit: Tube (EF86, E88CC)
• Connections:
  • Inputs: Mic/Line XLR (pin 2 hot), D/I (1/4”)
  • Output: XLR (pin 2 hot)
  • Transformer balanced I/O (custom wound)
• Controls:
  • Voltage gain: Stepped 16-52db
  • Fine gain: Stepped ±5db
  • Total gain: +57db
  • Output control: variable
  • Rumble filter: Inductor based, switchable (30,45,60,70,90,110,130,180hz)
  • PAD: 20db, switchable
  • Phase: 0/180º, switchable
  • Phantom Power: +48v, switchable
• Power: Internal power supply

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Warm Audio WA273-EQ

The Warm Audio WA273-EQ is a dual-channel, Class-A microphone preamp and equalizer designed to provide up to 80 dB of gain and 3-band EQ for engineers, producers, musicians, and vocalists in mobile-recording rigs and home, project, and commercial studios.

Link to the Warm Audio WA273-EQ product page.

• Description: Dual Channel, Class A, '73-Style British Microphone Preamp With EQ
• Components:
  • UK Made Carnhill Transformers
  • UK Made – Blore Edwards EQ Dual-Concentric Switch Potentiometers
  • Hand Wired, Hand Assembled
  • Fully Discrete
• Gain: 80 dB of Gain – Resistor Stepped Gain Switch
• Controls:
  • Tone Button: Changes Input Transformer Impedance For Varying Tone
  • Polarity Switch: In-Phase/Flipped-Phase
  • 48V Phantom Power: On/Off
  • Low Band Boost/Cut: 35, 60, 110, 220 Hz
  • Mid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 Hz
  • High Band Boost/Cut: 10, 12, 16 kHz
  • 4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 Hz
  • Output Control: Level
  • EQ: Dual-Concentric Switch Potentiometers
  • Gain: Resistor Stepped Gain Switch
• Inputs:
  • XLR Mic Inputs (Front & Back)
  • Line Level TRS Input
  • Direct In, Instrument Input
• Inserts:
  • TS Send/Receive Insert Jacks
• Outputs:
  • XLR & TRS Line Level Outputs
• Indicators:
  • LED Level Indication
• Frequency Response: 20 Hz – 20 kHz +/-.5 dB
• Mounting: 19″ Rackmountable
• Power: Internal IEC 115V/230V Power Inlet

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AEA TRP2

The AEA TRP2 is a great example of a ribbon microphone preamplifier designed with extra clean gain and an input impedance to suit the notoriously low-level signals of ribbon microphones. It even features +48V phantom power for active ribbon mics.

Link to the AEA TRP2 specifications sheet.

• Gain at 1 kHz: 85dB of gain at 1 kHz, balanced-in to balanced-out in Microphone Input mode
• Noise figure, rms A-weighted: <2dB
• Noise figure, rms unweighted: <3dB, 20 kHz LPF bandwidth
• EIN: <-130dBu A-weighted, 150 Ohm resistive source
• Frequency Response: -3dB <1Hz and >100 kHz
• THD: <0.02% at 1 kHz
• Input Impedance: 63K Ohms
• Input Impedance (P48 Engaged): 10K Ohms
• Mic Gain Control: Twelve-position switch provides from +7bD to +63dB of gain for the preamplifier circuit, as measured between the inputs and the before the output line driver.
• Output Level Potentiometer: 22dB
• Low-Cut Filter: 12dB per octave from 100 Hz
• XLR output maximum level into 600Ω load: +28 dBu, balanced; 0 dBu = 0.7746 V rms
• LED signal level indicators:
  • The green LED snaps on at -20 dBy to indicate the presence of signal;
  • The yellow LED snaps on at 0 dBu;
  • The red LED snaps on at +24dBu to warn of approaching signal overload
• Dimensions:
  • Half-rack wide, rack unit high (measured with knobs):
    8.5″ w, 8″ d, 1.8″ h (21.59 cm x 20.32 cm x 4.6 cm)
• Weight: 2.2lbs (1 kg)
• Power Supply Weight: 13 oz (0.37 kg)
• Power Supply Length: 7 feet 8.5 inches (2.3 m)
  • Power supply length may be supplemented with longer IEC cable