Amplifier Specifications – My New Microphone

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 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? 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, and etc.) I will list out 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. In order 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-ZBAE 1073DMP DesktopHeritage Audio 1084Chandler REDD.47Warm Audio WA273-EQ List Of Preamplifier Specifications DescriptionFeaturesCircuit/ComponentsInputsInput ImpedanceEquivalent Input NoiseNoiseInsertsGain (voltage and dB)OutputsOutput ImpedanceMaximum Output LevelTotal Harmonic DistortionCommon Mode Rejection RatioControlsGain Control (Voltage gain - Fine gain - Total gain)PADPhantom PowerTone ButtonPolarity SwitchOutput ControlRumble FilterEQ ControlsIndicatorsPower Supply & Requirements/ConsumptionMountingWeightDimensionsPackaging 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 in 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 Features The features section of a mic preamp specs sheets lists out important bullet points about the microphone preamplifier. This "spec" will included several other specifications that the the manufacturer believes should be accented. Examples BAE 1073DMP Desktop Features Built-in PSU for extra portabilityDI in and DI through48v for phantom powerSolid steel chassisSame 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 modeHigh shelf: Fixed at 12 kHzHi Q: Switches the Q of the mid bandMid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHzBass shelf: 220, 110, 60 and 35 HzHigh pass filter: 300, 260, 80, 50 HzLo pass filter: 6, 8, 10, 14, 18 kHzEQL: Turns equalizer ONPhase: Flips phase 180º 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 about how the circuits are constructed and of 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 TransformersUK Made – Blore Edwards EQ Dual-Concentric Switch PotentiometersHand Wired, Hand AssembledFully Discrete Inputs The inputs specification refers to, well, the inputs of the mic pre. Microphones generally connect via balanced 3-pin XLR cables and so that 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 InputDirect In, Instrument Input Input Impedance The input impedance of the mic preamp is an important specification since it is the effective load that the microphone (or other source device) must drive. In general, the input (load) impedance of a mic input should be about 10 times that output impedance of the microphone. 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 try 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 ohmsDI Input Impedance: ≅150k ohms Heritage Audio 1084 Microphone input impedance:HI: 1200 Ohm minimumLO: 300 Ohm minimumHigher gain positions gradually have greater impedances, optimum for low gain ribbon mics. Input is transformer balanced and floatingLine input impedance: 10KOhms bridging, transformer balanced and floating AEA TRP2 Input Impedance: 63K OhmsInput Impedance (P48 Engaged): 10K Ohms 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 component, 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 Noise Noise rating is similar to equivalent input noise except that it's absolute. Rather than the noise being compared to the output signal, it's compared to the threshold of no signal level. Examples AEA TRP2 Noise figure, rms A-weighted: <2dBNoise figure, rms unweighted: <3dB, 20 kHz LPF bandwidth 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 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 VoltsGain dB: 0 to 71 dB Heritage Audio 1084 Maximum Gain: Slightly greater than 80dB Chandler REDD.47 Voltage gain: Stepped 16-52dbFine gain: Stepped ±5dbTotal 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 modeMic 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. 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 OutputsOutput Control: Level 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 Maximum Output Level The maximum output level of a microphone preamp tells us just how much the preamplifier is capable of outputting. This spec, like most line level signal strength measurements, 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 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 and 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 Common Mode Rejection Ratio Microphones will typically output balanced audio signals via an XLR cable. Balanced signals are transferred as follows: Pin 1: common groundPin 2: positive polarity (hot) signalPin 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 that the preamp is capable of eliminating 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. To learn more about balanced microphone signals, check out my article Do Microphones Output Balanced Or Unbalanced Audio? Examples BAE 1073DMP Desktop Common Mode Rejection Ratio: 100dB min @ 60Hz Controls Preamps have controls for their circuits. Pretty much every preamp has a gain control that allows the user to manually adjust the gain applied to the signal. Most preamps will also have a phantom power switch (which is a form of control). However, there are plenty of other potential controls that a microphone preamplifier may have, especially if it has a built-in EQ. Examples Cloud Microphones CL-Z Input Impedance: 150 ohms to 15 kOhmsGain: +12 dB or +25 dB increase BAE 1073DMP Desktop Gain Voltage: 0 to 33.4 VoltsGain 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 modeHigh shelf: Fixed at 12 kHzHi Q: Switches the Q of the mid bandMid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHzBass shelf: 220, 110, 60 and 35 HzHigh pass filter: 300, 260, 80, 50 HzLo pass filter: 6, 8, 10, 14, 18 kHzEQL: Turns equalizer ONPhase: Flips phase 180º Chandler REDD.47 Controls: Voltage gain: Stepped 16-52dbFine gain: Stepped ±5dbTotal gain: +57dbOutput control: variableRumble filter: Inductor based, switchable (30,45,60,70,90,110,130,180hz)PAD: 20db, switchablePhase: 0/180º, switchablePhantom Power: +48v, switchable Warm Audio WA273-EQ Controls: Tone Button: Changes Input Transformer Impedance For Varying TonePolarity Switch: In-Phase/Flipped-Phase48V Phantom Power: On/OffLow Band Boost/Cut: 35, 60, 110, 220 HzMid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 HzHigh Band Boost/Cut: 10, 12, 16 kHz4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 HzOutput Control: LevelEQ: Dual-Concentric Switch PotentiometersGain: 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: 22dBLow-Cut Filter: 12dB per octave from 100 Hz 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 VoltsGain 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 16-52dbFine gain: Stepped ±5dbTotal 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. 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 allows 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 Phantom Power Phantom power is essential to power many of the condenser microphones on the marker 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 OhmsInput Impedance (P48 Engaged): 10K Ohms Tone Button A tone button or knob is included on some microphone preamps the will alter the circuitry of the preamp to alter the tonal characteristics of the output signal. Examples Warm Audio WA273-EQ Tone Button: Changes Input Transformer Impedance For Varying Tone 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 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 EQ Controls Some preamplifiers have EQ controls to help shape the signal. These EQs feature filters, shelves, and other boosts and cuts. Examples Heritage Audio 1084 High shelf: Fixed at 12 kHzHi Q: Switches the Q of the mid bandMid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHzBass shelf: 220, 110, 60 and 35 HzHigh pass filter: 300, 260, 80, 50 HzLo pass filter: 6, 8, 10, 14, 18 kHzEQL: 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 ToneLow Band Boost/Cut: 35, 60, 110, 220 HzMid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 HzHigh Band Boost/Cut: 10, 12, 16 kHz4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 HzEQ: Dual-Concentric Switch Potentiometers AEA TRP2 Low-Cut Filter: 12dB per octave from 100 Hz Indicators Indicators are typically lights that either flash/flicker or light up to indicate occurrences and states of performance of the microphone preamplifier. These indicator could tells us any of the following: Power onStandbySignalLimitPhantom power engagedPhase 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 Power Supply & Requirements/Consumption These specifications will either simply 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 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 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 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) 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) 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 lbBox Dimensions (LxWxH): 6.693 x 4.331 x 2.835″ 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. Cloud Microphones CL-Z The Cloud Microphones CL-Z (link to compare prices at select retailers) is "mic activator" preamplifier with Vari-Z (variable impedance) and Vari-HPF (variable high-pass filter) controls. Cloudlifter Z Link to check out the Cloud Microphone Cloudlifter Z specifications. I/O:1x XLR input1x XLR outputInput Impedance: 150 ohms to 15 kOhmsGain: +12 dB or +25 dB increasePacking info:Package Weight: 1.25 lbBox Dimensions (LxWxH): 6.693 x 4.331 x 2.835" BAE 1073DMP Desktop The BAE 1073DMP Desktop Mic Pre (link to compare prices at select retailers) 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 pre-amp circuit and the same Carnhill transformers as the 1073 and 1084. BAE 1073DMP Desktop Link to check out the BAE 1073DMP specifications. FeaturesBuilt-in PSU for extra portabilityDI in and DI through48v for phantom powerSolid steel chassisSame hand-wired modular design that BAE is known forFrequency Response: 10Hz to -3dB at 55kHzMic Pre Input Impedance: ≅1200 ohmsDI Input Impedance: ≅150k ohmsOutput Impedance: 65 ohmsCommon Mode Rejection Ratio: 100dB min @ 60HzMaximum Output Level: +27.4 dBu @ 600ΩPower Requirements: 115/230 VAC, 28WGain Voltage: 0 to 33.4 VoltsGain dB: 0 to 71 dBEquivalent Input Noise: -110 dBu; Unweighted 300kHz BandwidthWeight: 7.3 LBS/3.31 KGDimensions (Inches): 5.3W x 4L x 11D Heritage Audio 1084 The Heritage Audio 1084 (link to compare prices at select retailers) 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. Heritage Audio 1084 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 modeHigh shelf: Fixed at 12 kHzHi Q: Switches the Q of the mid bandMid peak band: 7.2, 4.8, 3.2, 1.6, 0.7, 0.36 kHzBass shelf: 220, 110, 60 and 35 HzHigh pass filter: 300, 260, 80, 50 HzLo pass filter: 6, 8, 10, 14, 18 kHzEQL: Turns equalizer ONPhase: Flips phase 180ºMicrophone input impedance:HI: 1200 Ohm minimumLO: 300 Ohm minimumHigher gain positions gradually have greater impedances, optimum for low gain ribbon mics. Input is transformer balanced and floatingLine input impedance: 10KOhms bridging, transformer balanced and floatingOutput impedance: Less than 75 Ohms, transformer balanced and floating, to drive a load of 600 OhmsMaximum output: Greater than +26dBu into 600 OhmsTHD: Less than 0.025% at 1Khz, Less than 0.05% at 100HzFrequency response: 20Hz (+0.3dB) to 20Khz (-0.2dB)Maximum Gain: Slightly greater than 80dBNoise: Less than -100dBuPower consumption: Less than 110 mA @24VDC Chandler REDD.47 The Chandler REDD.47 (link to compare prices at select retailers) 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. Chandler REDD.47 Link to the Chandler REDD.47 product page. Channels: MonoCircuit: 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 16-52dbFine gain: Stepped ±5dbTotal gain: +57dbOutput control: variableRumble filter: Inductor based, switchable (30,45,60,70,90,110,130,180hz)PAD: 20db, switchablePhase: 0/180º, switchablePhantom Power: +48v, switchablePower: Internal power supply Warm Audio WA273-EQ The Warm Audio WA273-EQ (link to compare prices at select retailers) 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 EQComponents:UK Made Carnhill TransformersUK Made - Blore Edwards EQ Dual-Concentric Switch PotentiometersHand Wired, Hand AssembledFully DiscreteGain: 80 dB of Gain - Resistor Stepped Gain SwitchControls:Tone Button: Changes Input Transformer Impedance For Varying TonePolarity Switch: In-Phase/Flipped-Phase48V Phantom Power: On/OffLow Band Boost/Cut: 35, 60, 110, 220 HzMid Band Boost/Cut: 360, 700, 1600, 3200, 4800, 7200 HzHigh Band Boost/Cut: 10, 12, 16 kHz4-Position Inductor Based Hipass Filter: 50, 80, 160, 300 HzOutput Control: LevelEQ: Dual-Concentric Switch PotentiometersGain: Resistor Stepped Gain SwitchInputs:XLR Mic Inputs (Front & Back)Line Level TRS InputDirect In, Instrument InputInserts:TS Send/Receive Insert JacksOutputs:XLR & TRS Line Level OutputsIndicators:LED Level IndicationFrequency Response: 20 Hz - 20 kHz +/-.5 dBMounting: 19" RackmountablePower: Internal IEC 115V/230V Power Inlet AEA TRP2 The AEA TRP2 (link to compare prices at select retailers) 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. AEA TRP2 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 modeNoise figure, rms A-weighted: 100 kHzTHD: <0.02% at 1 kHzInput Impedance: 63K OhmsInput Impedance (P48 Engaged): 10K OhmsMic 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: 22dBLow-Cut Filter: 12dB per octave from 100 HzXLR output maximum level into 600Ω load: +28 dBu, balanced; 0 dBu = 0.7746 V rmsLED 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 overloadDimensions: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 AEA is featured in My New Microphone's Top 13 Best Microphone Preamplifier Brands In The World.