We've all got used to the idea of DI boxes — little devices that allow high impedance instruments to be directly interfaced with low impedance mixer inputs. MTR's GB2 Gain Brain does a similar job, in that it boosts the level of a low level signal so that it can be interfaced with a wider range of inputs. Potential uses include matching levels between an acoustic guitar bug and a combo, allowing a mic to be plugged directly into an effects unit, keyboard level matching, boosting low output mics to feed low gain mixer inputs and so on.

The GB2 is a simple unit, rather like other similarly sized products in MTR's range. It's a small battery powered device with a minimum of controls, although it has recently been upgraded to derive current from phantom power. It will work with either balanced or unbalanced signals, though balanced connections are on stereo jack rather than XLR connector. Although the GB2 is a basic unit, it can be customised a little to suit your needs. If distortion occurs in your particular application, there is an internal input sensitivity preset that can be adjusted. Perhaps this should have been brought to some external point, or an access point drilled in the top of the box, since the lid has to be taken off every time it is necessary to alter the sensitivity. However, it is likely that the Gain Brain will most often be used to fix a particular problem, so that regular alteration of this value won't be necesary. The mic input has a range of 10mV to 50mV RMS, and the output has a range of 30mV to 160mV RMS. Also, the line output also has three (externally) selectable settings of -10dB, 0dB and +4dB, making the unit compatible with a wide range of equipment. In fact the high impedance line input (1MOhm) would be suitable for passive (piezo electric) acoustic guitar pickups, which need a high impedance input; electric guitars and basses could also be plugged in at a pinch.

Power comes from an internal 9V PP3 type battery or external mains adaptor; the GB2 switches on when you connect something to its output. In use, the box succeeded in bringing up the available level of dynamic mics, though any low level source would benefit — if you are presenting a higher level to your mixer or effects input, the input doesn't have to work as hard, with a resulting lowering of background noise and distortion. Some acoustic guitar pick-ups actually work without batteries, with a correspondingly low output — the GB2 is perfect for such a circumstance. Likewise, the outputs of many synths could do with a boost. If you find that you have a mic or instrument that never seems to be very loud, and forces you to have the gain controls cranked full up all the time to get usable level, then there could be a mismatch: MTR's little box could be the problem solver for you.

Like a DI box, you'll probably pick up a Gain Brain to solve a specific problem. But if you're getting a variety of musicians moving through your studio, or have a high turnover of older equipment, you might like to keep one or two around — especially at this price. The GB2 offers a simple and inexpensive workaday solution to a problem that will often creep up on you unawares, and at just under £40 it's a bit of a steal.

Further Information

GB2 Gain Brain £39 inc VAT.

MTR Ltd, (Contact Details).