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 PFA for a positive polarity output from the PFA. Most three-terminal microphones have a positive polarity output, and thus should be connected to a noninverting input PFA.
Some three-terminal low-voltage microphones may be connected to a balanced input PFA 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 TA3M and Shure TA4M formats, unless otherwise requested.
3.5mm minijack adaptor wiring configuration
There are several common methods of wiring input jacks for miniplug microphones, which are not fully compatible. The PFA adaptor can be supplied to support the following formats:
- Mono PC microphone (Soundblaster® format): tip = signal (6.8KΩ termination to ground); ring = power (+8V across 2kΩ); sleeve = ground.
- Mono plug-in power (“PIP”): tip & ring = signal + power (+8V across 6.8KΩ); sleeve = ground.
- Mono Sennheiser® compatible: tip = signal + power (+8V across 6.8KΩ); ring = no connection; sleeve = ground.
- Stereo plug-in power (“PIP”): tip = left + power (+8V across 6.8KΩ); ring = right + power (+8V across 6.8KΩ); sleeve = ground.
A microphone wired with separate signal (tip) and power (ring) leads will only be compatible with the PC microphone format.
Some microphones intended for use with PCs are wired with tip and ring as common for signal and power. Such microphones will work with any of the above PFA formats, but will work best with a mono PIP or Sennheiser® format adaptor.
Mono microphones wired with tip-sleeve (no ring) connectors or with tip-ring-sleeve with ring and sleeve in common will only be compatible with Sennheiser® format.
Mono microphones wired with tip-ring-sleeve connectors with ring unconnected will not work with the PC adaptor format, but will work with mono PIP or Sennheiser® format.
Stereo PIP miniplug microphones are normally wired as:
- tip: left signal + power
- ring: right signal + power
- sleeve: ground
That format is only compatible with the stereo minijack PFA phantom power adaptor. A PFA configured with stereo PIP format will have two XLR outputs; the XLR connected to the 3.5mm minijack ring terminal will be identified with a red ring on the XLR boot.
The voltage and resistance on the PFA’s microphone power supply can be customized as required.
“DI” instrument input
The PFA can support high-impedance instrument “DI” input using a special high-impedance amplifier, with either a ¼” TS (unbalanced) or TRS (balanced) phone plug input connector. The DI input version does not pass phantom power to connected instruments.
“Active” remote capsule microphones and polarization voltage
The PFA can support a range of “active” remote capsule, externally polarized condenser microphones that require a high polarization voltage. The standard barrel PFA can 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 extended barrel PFA may be ordered with 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 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.
A standard PFA 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 a PFA with polarization circuit, as that circuit will generate a fixed polarization voltage irrespective of phantom supply voltage.
tinybox format input
A PFA can be supplied with a TA6M 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.
Note that a PFA 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 PFA must be configured for a single microphone type.
It is also not possible for a PFA to supply 48V phantom power to a connected microphone, although a PFA can be configured to provide 12V or 16V phantom power (from a 48V supply) to a connected microphone with limited current draw (3mA or less).
Schoeps® KCY compatible input
A PFA can be configured to support the Schoeps KCY format via a Binder series 711-5-F input. However, the Binder connector does not support adequate cable diameter to allow for a stereo Y cable. Thus, it is necessary to have the stereo PFA terminated to a 5- or 6-pin mini-XLR (TA5M or TA6M), and use a short Binder to mini-XLR adaptor cable. The TA5 option is wired in the same pin configuration as the Schoeps KCY Binder (that is, pin 1 to pin 1, pin 2 to pin 2, etc.), whereas the TA6 option will be wired in a compatible “tinybox” format, as described above.
The Lectrosonics®-compatible TA5M configuration does not support Lectrosonics’ “Servo Bias” function; however, the PFA 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 instrument input
The Shure®-compatible TA4M configuration may support both microphone and instrument input upon request. To enable this feature, the high-impedance amplifier is used (see specifications below).