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:
- low-voltage supply
- right noninverting input
- left noninverting input
- polarization voltage supply
- right inverting input
- left inverting input
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.
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).
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).