IFA Specification

IFA inline phantom-powered amplifier

The IFA is an inline phantom power adaptor and amplifier designed to connect a full range of options for input devices to standard phantom-powered microphone inputs:

  • dynamic ribbon and moving-coil microphones, with +26dB gain
  • high-impedance instrument “DI” input
  • low-voltage microphones
  • “active” remote capsule microphones
  • 12V T-powered microphones

Input polarity and output configuration

The IFA is available in a wide range of input connectors and may be customized as required for each microphone type.  Select the input tab above for details.

The IFA can support noninverting or inverting input from a balanced or unbalanced microphone.  An unbalanced input IFA will provide an impedance- or electrically-balanced output.  The IFA can also support balanced interconnection for any microphone via independent noninverting and inverting inputs.  Note that an IFA in this configuration is not a differential circuit (and thus will not cancel interference by itself), but when connected to a standard differential input microphone amplifier will complete a fully balanced circuit from microphone to amplifier.  It is also possible to invert polarity with the balanced input option, if required.

The transformer-input option for dynamic microphones provides a balanced, differential input and output.

Input configuration

Low-voltage microphone input

Low-voltage microphones are wired as either two-terminal (signal + power and ground) or three-terminal (power, signal, and ground) devices.  Most two-terminal microphones have a negative polarity output, and thus should be connected to an inverting input IFA for a positive polarity output from the IFA.  Most three-terminal microphones have a positive polarity output, and thus should be connected to a noninverting input IFA.

Some three-terminal low-voltage microphones may be connected to a balanced input IFA in a “pseudo-balanced” configuration–the impedance on each terminal may not exactly match, but this configuration can still offer some rejection of interference compared with the unbalanced three-terminal configuration.  This “pseudo-balanced” configuration will be supplied with compatible microphone formats, including Audio-Technica TB3M and Shure TB4M formats, unless otherwise requested.

Dynamic microphone input

For dynamic microphones, the IFA offers two options; either a transformer-balanced or transformerless input.  The transformerless input version draws 4mA current vs. 1.2mA for the transformer-input version.  Either version offers low input noise and +26dB gain. The dynamic microphone input versions do not pass phantom power to connected microphones.  The transformer-input version offers a differential, balanced input and output; the transformerless version has balanced input and output, but does not feature a differential input and requires connection to a differential input microphone preamplifier to complete a balanced circuit.

T-power microphone input

For T-power microphones, +12V power can be applied to either input pin on the XLR-3-F connector.  A T-power adaptor IFA will be wired for balanced, noninverting input, unless inverting input is requested.  Please indicate powered pin and input polarity in the order notes.  A minimum phantom power supply voltage of +24V is required for T-power input.

“DI” instrument input

The IFA can support high-impedance instrument “DI” input using a special high-impedance amplifier, with either a ¼” TS (unbalanced) or TRS (balanced) phone jack input connector.  The DI input version of the IFA uses an extended XLR-3-M connector for its output.  The DI input version does not pass phantom power to connected instruments.

The ¼” input jack has its shield connected to the IFA chassis and the XLR-3-M pin 1.  If an isolated ground for the connected instrument is desired, order the ¼” TRS input version with mono electrically-balanced output, and use a custom ¼” TS to TRS input cable with its TS shield connected to TRS ring, and the cable shield connected at the TRS end only.

tinybox format input

An IFA can be supplied with a TB6M connector in “tinybox” format input, as follows:


  1. low-voltage supply
  2. right noninverting input
  3. left noninverting input
  4. polarization voltage supply
  5. right inverting input
  6. left inverting input
    chassis: ground

Each signal input pin may also provide a low-voltage microphone supply, as required.  Please specify microphone type in the order comment field.

In this format, the IFA will have either an XLR-3-M (stereo unbalanced) or XLR-5M (stereo balanced) output connector.

Note that an IFA cannot support multiple microphone types by providing two different low-voltage microphone supplies (on pin 1 and pins 2-3, 5-6), as was possible with a tinybox.  Thus, each IFA must be configured for a single microphone type.

Lectrosonics®-compatible input

The Lectrosonics®-compatible TB5M configuration does not support Lectrosonics’ “Servo Bias” function; however, the IFA can be made compatible with mics wired for “Servo Bias”.   Please specify your microphone’s wiring format according to the Lectrosonics schematic.

Sennheiser®-compatible instrument input

The Sennheiser®-compatible ¼” TRS configuration may support both microphone (tip) and instrument (ring) input upon request.  To enable this feature, the high-impedance amplifier is used (see specifications below).

Shure®-compatible input

The Shure®-compatible TB4M configuration may support both microphone and instrument input upon request.  To enable this feature, the high-impedance amplifier is used (see specifications tab above).

Custom options

“Active” remote capsule microphones and polarization voltage

The IFA can support a range of “active” remote capsule, externally polarized condenser microphones that require a high polarization voltage.  An IFA configured to support “active” remote capsule microphones will contain a polarization circuit that outputs a fixed voltage (between +40V and +60V), as required by the microphone, at any phantom supply voltage (+12-48V).

The polarization circuit may be omitted, if desired.  Without the polarization circuit, the IFA will provide a +40V rail for the polarization supply when used with a standard +48V phantom power supply. The polarization voltage will be correspondingly lower with low-voltage (P12, P24, or any nonstandard voltage) phantom power.

The connected microphone’s sensitivity, self-noise, and SPL handling will vary with the polarization voltage, such that +40V supply will yield -3.5dB sensitivity (and 3.5dB higher self-noise and SPL handling) compared with a +60V supply. A low-voltage supply will yield even lower sensitivity.

An IFA without the polarization circuit connected to a microphone amplifier with selectable phantom voltage can thus offer two sensitivity levels, acting as a capsule attenuator and resulting in increased SPL handling at the lower phantom voltage. For example, a P12 phantom supply will yield -12dB sensitivity (and thus 12dB higher SPL handling) as compared to a P48 phantom supply. This effect will not occur using an IFA with polarization circuit, as that circuit will generate a fixed polarization voltage irrespective of phantom supply voltage.

Output configuration

The IFA is available with the following outputs:

  • XLR-3-M: mono input, impedance- or electrically-balanced output
  • XLR-3-M: stereo unbalanced output
  • XLR-5-M: stereo input, impedance- or electrically-balanced output
  • XLR-5-M: four-channel unbalanced output

The XLR-5-M output uses an extended connector for its output.  TBxM and 1/4″ input connectors also require an extended XLR-x-M output connector.  Extended XLR-3-M connectors are available as an option for other configurations, if direct connection to microphone preamplifiers is desired.

Output cables

Special output cables are available in these formats:

  • XLR-3-F to dual XLR-3-M (impedance-balanced)
  • XLR-3-F to stereo XLR-5-M (impedance-balanced)
  • XLR-5-F to dual or quad XLR-3-M

IFA inline adaptor and amplifier specification:

Type: inline phantom power adaptor and amplifier for dynamic, T-power, low-voltage, and “active” remote capsule microphones; DI instrument adaptor.

Phantom Power: +9-52V; +24V minimum required for 12T and +16V “active” microphones.
Voltage Supplied to Microphones: low-voltage; +8V, “active”; +6-16V; 12T, +12V.
“Active” Polarization Voltage: +60V maximum

Current, low-voltage microphone, electrically-balanced output: 2mA typical
Current, low-voltage microphone, impedance-balanced output: 1mA typical
Current, low-voltage microphone, stereo electrically-balanced or four-channel output: 4mA typical
Current, transformer-input dynamic mic or DI input: 1.2mA
Current, transformerless dynamic mic input: 4mA
Polarization voltage circuit: 1.2mA

Input Impedance: 6kΩ or as specified
Input Impedance, dynamic microphone, transformer input: 6kΩ
Input Impedance, dynamic microphone, transformerless input: 12kΩ
Input Impedance, DI input: 1.6MΩ
Output Impedance: 150Ω
Recommended Preamp Input Impedance: 1.5kΩ or higher

Maximum Input Level, 1kHz @ 1% THD: +6dBV (8V mic supply) to +13dBV (16V mic supply)
Maximum Input Level, 1kHz @ 1% THD, +26dB dynamic mic input: -15dBV (with P48 supply)
Maximum Input Level, 1kHz @ 1% THD, transformer input: -12dBV (with P48 supply)

Total Harmonic Distortion, 1kHz @ -30dBV: less than 0.005%
Total Harmonic Distortion (transformer input) 1kHz @ 0dBV output: 0.01%
Total Harmonic Distortion (transformer input) 100Hz @ 0dBV output: 0.1%

Frequency Response: 20Hz to 40kHz
Frequency Response (transformer input, 150Ω source): 30Hz to 20kHz

Equivalent Input Noise, electrically-balanced output: -121dBV unweighted, -124dBA
Equivalent Input Noise, impedance-balanced output: -124dBV unweighted, -127dBA
Equivalent Input Noise (low-noise dynamic microphone version): -125dBV unweighted, -128dBA
Equivalent Input Noise (transformer-input dynamic microphone version): -127dBV unweighted, -130dBA
Equivalent Input Noise, high-impedance input: -117dBV unweighted, -120dBA

Weight:  81g (2.8oz)
Dimensions:  87mm x 32mm x 25mm (3 1/2″ x 1 1/4″ x 1″)
Dimensions (extended output):  106mm x 32mm x 25mm (4 1/8″ x 1 1/4″ x 1″)

Notice of FCC compliance

Pursuant to section 15.103(h), the IFA with polarization circuit is only intended to be run from a battery-powered phantom power supply or microphone preamplifier.  It is thus exempt from Part 15 of the FCC rules.  The IFA qualifies for exemption as the highest frequency generated by the device is less than 1.705MHz, and it may not be operated from the AC power lines.  Use of an IFA with polarization circuit connected to a phantom power supply or microphone preamplifier that is operated from the AC power lines is strictly prohibited under Part 15.