GB-2

  "Gain Brain" Mic to Line Booster - User Guide

The Gain Brain is a pre-amp designed to boost mic signals, both balanced (use a stereo jack plug)* and unbalanced, and instrument signals through their own dedicated input sockets, up to line levels of -10dB, 0dB or +4dB.  The unit is ultra quiet in operation, and uses include as a pre-amp for acoustic instrument 'bugs', plugging a mic direct into a line level effects unit or slave amp, keyboard level-matching, boosting low output mics to feed low gain mixer inputs etc.

The sensitivity of both mic and line inputs can be adjusted by removing the top cover, and using a small blade screwdriver to alter the pre-set gain pot to the right of IC2 on the circuit board.  Turn to the left if distortion is occurring, and to the right if more gain is needed.

The output level is determined by setting the switch to the required position, i.e. -10dB, 0dB or +4dB

The Gain Brain can be powered in two ways: by a 9 volt 'PP3' battery (not supplied), which is fitted by removing the lid and connecting the battery terminals. It is switched on and off by the insertion and removal of a jack plug in the output socket.  Always ensure that this plug is disconnected after use to prolong battery life.  A battery-low led warns that the battery needs changing.

Alternatively, use an external 9v DC power supply plugged into the DC input socket.  N.B: make sure it has the same polarity as printed on the lid - centre pin negative, outer ring positive.  The power supply must be regulated, un-regulated supplies will almost certainly cause hum.

* NOTE: since 2005 the stereo jack socket for microphones has been replaced with an XLR socket

SPECIFICATIONS

Mic Input:  Sensitivity adjustable from 10mV to 50mV RMS.  Impedance 600 ohms to 47Kohms, balanced or unbalanced
Instrument Input:  Sensitivity adjustable from 30mV to 160mV RMS  Impedance: 1 Megohm
Output:  -10dB, 0dB, +4dB selectable
Signal to Noise:  Better than 82dB ref. 30mV input
Frequency Response:  Mic: 15Hz -20KHz ±3dB, Line: 15Hz - 50KHz ±3dB
Battery Low led:  Illuminates at approx. 4.5 volts

Download the MTR e-book from the home page of our website.  We welcome owner/user feedback.

MTR Ltd, Ford House, 58 Cross Rd, Bushey, Herts, WD19 4DQ   UK
Tel: +44-(0)1923-234050   Fax: -255746    e-mail: mtrltd@aol.com    www.mtraudio.com