Conford Electronics
 Professional Audio and Process Control
Headphone Amplifier Box
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Stereo Headphone Amplifier Box
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This transformerless design compliments the Balance Box but enables any microphone amplifier (with or without a transformer coupled input) to be converted to P48 standard phantom power. Line balance is accurately defined to ensure common mode interference rejection is not degraded, an important feature when phantom powering remotely from the microphone amplifier. Full protection is provided against line shorts or the plugging in of microphones damaging the microphone amplifier input with large voltage transients.

Close tolerance components (0.1%) provide matched DC feeds to the microphone leads and a low noise 48 volt supply ensures noise performance is not compromised. A low impedance DC isolated output allows moderately long signal lines to be driven to the microphone amplifier without deterioration in frequency response or line balance. This enables the phantom powering to be applied close to the microphone avoiding long signal lines carrying 48 volts with the risk of losses and microphonic effects in the cable. A switchable 20 dB attenuator is provided to take into account the higher signal levels produced by many professional condenser microphones. Some microphones have the facility to operate from an internal single cell battery, but used in this way performance is adversely affected.

An extremely compact high efficiency step-up switching converter gives exceptional battery life from a single PP3. Provision is made for the connection of an external supply should this be required. Great care has been taken to avoid induction of switching products onto the signal lines and external eletromagnetic radiation is minimised by thorough screening.

Connection to balanced microphone amplifiers

To connect to the Balance Box, or any other balanced microphone amplifier, the output of the Phantom Power Box is connected directly to the amplifier input with both signal lines, together with the screen. The microphone is similarly connected to the input of the power unit with both signal lines and screen. Use only high quality cable for the microphone lead.

With the Balance Box a balanced or unbalanced line output can be obtained without disturbing the balance of the microphone lines. With both Phantom powering and amplification being performed close to the microphone maximum protection against interference is obtained.

Connection to unbalanced microphone amplifiers

Powering must always be provided through both microphone modulation leads and neither should ever be connected to ground at the input to the Phantom Power Box. The DC isolated output of the Phantom Power Box may be connected to an unbalanced microphone amplifier by either grounding or floating the unused signal lead (usually pin 3, with pin 2 the in phase signal) depending on the design of the microphone in use. Check the manual supplied with the microphone for the recommended method in any particular application.

Because of their interference suppression properties balanced lines should always be used in professional installations.


Conford, Liphook, Hampshire, GU30 7QW, UK
+44 (0)1428 751469
Webmaster: John
10 - Phantom Power Box Specification
The Phantom Power Box

A precision 48 volt microphone phantom power supply
Exceeds the requirements of DIN 45596
Phantom Power Box