The RB-MA1 consists of a low noise microphone pre-amplifier for converting mic level signals to line level, or for driving long lines from microphones to mixing equipment.
 
The connections and controls are on the rear panel. The microphone input is an XLR-3 type and is electronically balanced. The gain for the input can be adjusted by a recessed pre-set potentiometer which allows for the use of both dynamic and powered microphones.

The line output is of an XLR-3 type and is electronically balanced. It can be wired unbalanced by grounding the non-phase signal, allowing you to feed both balanced and unbalanced equipment.

There is a switch to control a high pass filter (low frequency roll-off at 125Hz) and to provide phantom power at +48V to the connected microphone.