The IPA flexible power inline microphone amplifier, adaptor, and power supply
The IPA flexible power microphone amplifier is an inline amplifier, power adaptor, and power supply that supports a wide range of microphones, including low-voltage, “active” remote capsule microphone systems, high-impedance instrument “DI” input, and a low-noise transformer-input version for moving-coil and ribbon dynamic microphones. The IPA is available in both mono and stereo configurations.
The IPA is not a differential amplifier in most configurations. The IPA is a two-channel single-ended noninverting amplifier that can run in a balanced configuration only if the microphone and receiving amplifier are also balanced output and input, respectively. The exception is for the transformer-input version, which is transformer-balanced input to impedance-balanced output and thus does operate as a differential amplifier. In balanced configurations, the IPA is mono only. Stereo configurations are always unbalanced.
Stereo “plug-in power” microphones are supported with a TB3M mini-XLR input connector. For superior reliability, the microphones should be directly terminated with a mating TA3F connector (pin 1, ground; pin 2, left; pin 3, right; or as specified). Alternatively, a minijack to TA3F adaptor cable may be used, or the auxiliary optional minijack may be configured as a parallel input rather than output (see below under Output configuration).
The “tinybox format” TB6M connector can support multiple microphone types using custom adaptor cables, or instead can support stereo input and output using a minijack & miniplug splitter cable. Please inquire for custom configurations. The IPA’s TB6M connector is wired slightly differently than a tinybox, so not all microphone configurations can be supported as with a tinybox. The IPA’s TB6M pin configuration is:
2 right input (noninverting)
3 left input (noninverting)
4 polarization voltage (+60V) or low-voltage supply (+8V)
5 low-voltage supply (+8V) or right auxiliary output
6 low-voltage supply (+8V) or left auxiliary output
The noninverting inputs may also have low-voltage supply (+8V) or termination to ground as required. Polarization voltage may be customized from +40V to +60V as required.
The IPA may have an optional three-position gain switch. The gain switch may be set with either a spindle (shown) or a screwdriver slot (3mm flathead). Standard gain settings are 0dB, +9dB, and +18dB. The middle position (or fixed gain) may also be configured for pre-emphasis (+9dB above 3kHz, AES-compatible; or custom setting as specified).
The dynamic microphone input version has standard gain settings of +9dB, +18dB, and +27dB, with minimum gain of +9dB (due to input transformer) and maximum available gain of +36dB.
Versions without the gain switch may be configured with fixed gain from 0dB to +27dB (+9dB to +36dB for the dynamic microphone input version).
The IPA has a flexible power supply scheme that can support:
- +9V to +52V phantom power
- an internal A23 battery (battery not included)
- external battery or AC adaptor via DC power port (+5V to +15V; +12V recommended)
The highest voltage supply will prevail, so when an internal A23 battery is installed, phantom power voltage of at least +18V or external supply voltage of +12V must be present to switch to phantom or external power operation. If the phantom or external voltage supplied is lower, the internal A23 battery must be removed or the IPA may continue to operate on internal battery. The external power jack is 1.7mm ID, 4.4mm OD, center-positive. A compatible power supply is available on the X-R accessory menu.
The A23 battery is accessed by removing the thumbscrews and then the bottom panel of the case.
The IPA has a dual green/red LED to indicate power source: red for phantom or external power; green for internal A23 battery; yellow for internal low battery condition.
The IPA draws 2mA for stereo versions and 1mA for mono versions. Autonomy with an A23 battery is 20 hours for stereo versions and 50 hours for mono versions. Versions for “active” remote capsule microphone system will require a high-voltage polarization circuit which draws an additional 1.5mA, for autonomy of 10 hours for stereo versions and 16 hours for mono versions. The current draw of the connected microphone must be added to the IPA’s current draw to derive total current consumption. This is typically less than 0.5mA per microphone for low-voltage microphones and up to 1mA per microphone for “active” remote capsules.
The IPA circuit (except the dynamic microphone input version) monitors the current draw on its input connector. When the input is not connected, the amplifier circuit will shut down and the circuit will draw an idle current of 40μA. This idle current will drain an A23 battery in approximately two months. If the IPA is not to be used for longer than a week, the battery should be removed to prevent discharge.
The IPA for dynamic microphone input is configured such that the battery is not connected unless pin 1 is bridged to the IPA case at the input XLR-3-F connector. Thus, the battery will not be drained unless a microphone or cable with pin 1 to case termination is attached. Most dynamic microphones have that internal connection, so it is recommended that the IPA be directly attached to the microphone. If the IPA must be remote from the microphone, then the microphone cable must have its pin 1 bridged to the shell on its XLR-3-M connector.
The IPA input is noninverting. A stereo IPA has the left output on pin 2 and the right output on pin 3 of the XLR-3-M output connector. The optional stereo XLR output cable routes the IPA output pins 2 and 3 to pins 2 of the cable’s dual XLR outputs, with impedance-balancing networks on pins 3. This will result in positive polarity when connected to balanced XLR input microphone amplifiers. If the IPA outputs need to be inverted, the cable can also be constructed with output on pins 3.
A mono IPA has an impedance-balanced output with signal on pin 2 and an impedance-balancing network on pin 3. When a mono IPA is connected to a balanced XLR input microphone amplifier with a standard XLR microphone cable, the resulting signal will have also have positive polarity.
When operating on internal battery or external power, the IPA’s XLR-3-M output may be directly connected to any stereo unbalanced input with the miniplug output cable. There will be no DC voltage present on the XLR output when phantom power is not present.
The IPA may also have an optional minijack output. The IPA case length is extended to accommodate the optional minijack output.
The optional minijack may also be configured as a parallel input with the TB3M input configuration, to enable use of “plug-in power” microphones terminated to a 3.5mm miniplug, without requiring the use of an adaptor cable. With that option, the only output is the XLR-3-M.
An IPA with TB6M connector may have both input and output on the TB6M connector; see pin configuration above.
Adaptor cables for the IPA’s input connector may be configured using the custom cable menu.
IPA flexible power inline microphone amplifier specifications
Phantom Power Input: +9 to +52V
External Power Input: +5 to +15VDC; +12VDC recommended; minimum +12VDC required when internal A23 battery installed
Current (stereo, exclusive of microphone current): 2mA
Current (mono, exclusive of microphone current): 1mA
Current, polarization circuit: additional 1.5mA
Current (idle, input not connected): 40μA
Autonomy (A23 battery, stereo): 20 hours
Autonomy (A23 battery, stereo “active”): 6-10 hours
Autonomy (A23 battery, mono): 50 hours
Autonomy (A23 battery, mono “active”): 10-16 hours
Low-voltage Power to Microphones: +10V
Polarization Voltage to Microphones: +40V to +60V, as specified
Input Impedance (low-volt microphone, typical): 6KΩ or as specified
Input Impedance (DI): 1.6MΩ
Output Impedance: 75Ω (each pin); 150Ω (dual XLR stereo output cable)
Output Impedance, optional minijack: 600Ω (each pin)
Recommended Preamp Input Impedance; XLR output: 1.5KΩ or higher
Recommended Line Input Impedance; minijack output: 5KΩ or higher
Maximum Input Level, 1kHz @ 1% THD, 0dB gain, phantom power, 1kHz @ 1% THD: +10dBV
Maximum Input Level, 1kHz @ 1% THD, 0dB gain, A23 battery power, 1kHz @ 1% THD: +8dBV
Maximum Input Level, dynamic mic input, 1kHz @ 1% THD, +11dB gain, phantom power, 1kHz @ 1% THD: -1dBV
Maximum Input Level, dynamic mic input, 1kHz @ 1% THD, +11dB gain, A23 battery power, 1kHz @ 1% THD: -3dBV
Total Harmonic Distortion, 1kHz @ 0dBV output: less than 0.005%
Total Harmonic Distortion (dynamic mic input) 1kHz @ 0dBV output: 0.01%
Total Harmonic Distortion (dynamic mic input) 100Hz @ 0dBV output: 0.1%
Frequency Response: 20Hz to 20kHz (-0.3dB @ 20Hz)
Frequency Response (dynamic mic input, 150Ω source): 30Hz to 20kHz
Noise: -121dBV unweighted, -124dBA
Noise (low-noise dynamic microphone version): -127dBV unweighted, -130dBA
Weight (standard): 91g (3.2oz)
Weight (extended): 100g (3.5oz)
Dimensions (standard): 93mm x 32mm x 25mm (3 5/8″ x 1 1/4″ x 1″)
Dimensions (extended): 111mm x 32mm x 25mm (4 3/8″ x 1 1/4″ x 1″)
Notice of FCC compliance
Pursuant to section 15.103(h), the PFA with +60V polarization voltage is only intended to be run from internal battery or a battery-powered phantom power supply or microphone preamplifier. It is thus exempt from Part 15 of the FCC rules. The PFA 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 a PFA with +60V polarization voltage connected to a phantom power supply or microphone preamplifier that is operated from the AC power lines is strictly prohibited under Part 15.