Conford Electronics
 Professional Audio and Process Control
Headphone Amplifier Box
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Stereo Headphone Amplifier Box
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The Balance Box provides matching of impedance, amplification, suppression of crosstalk, and rejection of electromagnetic interference at frequencies in the range 10 Hz to 1 GHz. This is achieved without using heavy matching transformers that limit audio performance.

The use of close tolerance (0.1%) components and a state of the art transformerless design enables the unit to operate with a wide variety of inputs, either balanced or unbalanced, with low noise and distortion, while operating from a single PP3 battery. Extended frequency response with low phase shift results in superior transient performance compared to transformers. The true floating nature of the circuit enables both input and output to be configured as balanced or unbalanced, in either the microphone or line modes at all gain settings, without change to the nominal stage gain selected. Comprehensive protection from radio frequency interference is provided by the balancing of the lines, low pass filtering and screening.

The excellent distortion, noise and common mode rejection (i.e. interference cancellation) performance enables the device to be used where a high quality audio signal is required, e.g. digital front ends, as well as educational, news gathering, live music recording, public address, entertainment, multimedia and industrial purposes. With the ability to operate from an external standard linear 9 volt regulated DC mains adaptor the unit is suitable for both permanent and temporary installations.

Typical microphone modes of operation

With long microphone cable runs, the Balance Box can be used, with either balanced or unbalanced microphones, and, with switchable gain in the range 20 dB to 50 dB in 10 dB steps, to provide a low impedance high level output for driving long balanced lines particularly advantageous in electrically noisy environments. With short microphone cable runs, the Balance Box can be used as a high quality balanced preamplifier driving an unbalanced input directly.

Typical line modes of operation

With such sources as CD, DAT, Cassette, MP3 players and PCs, the Balance Box can be used as a line input device with a high bridging input impedance and gain selectable in the range -10 dB to +20 dB to convert an unbalanced output to a low impedance balanced line output. For stereo sources a balanced mono signal can be obtained by resistively summing the left and right outputs into the Balance Box input. For stereo two units are required.

Conversely, the Balance Box may be used to convert an unbalanced input on mixing desks, control centres, cassette and DAT recorders, etc. to a balanced input where this facility is not available or is of inadequate performance.


Conford, Liphook, Hampshire, GU30 7QW, UK
+44 (0)1428 751469
Webmaster: John
8 - Balance Box Microphone Amplifier Specification
The Balance Box
The Balance Box Microphone Amplifier

A precision microphone or line amplifier for balanced or unbalanced signals producing clean low distortion audio of the highest technical quality