Most of the DI boxes we've looked at are either passive devices based around a matching transformer, or transformerless active systems. The Klark Teknik model combines the benefits of both types by adding transformer matching and isolation to a low-noise active circuit, power being derived from a standard phantom powering system.

Either XLR or jack inputs (High Z, 1M ohm nominal) can be accommodated and both are balanced, though the jack inputs may be used unbalanced simply by inserting a mono jack. There are two parallel jacks so that a signal may be fed into one jack and out of the other if the DI box is to be used for tapping off signal, say, for a PA feed.

The output is on a balanced, low Z (150ohms) XLR connector designed to be fed into the mic input of a mixer — and of course this input must have phantom power in order to operate the DI box. Because the circuit contains a transformer, the input and output may be completely isolated, but an Earth Link switch is provided for those applications that demand continuity of ground from input to output. Also included are switches for a 30dB pad and a 15dB attenuator which will be necessary when incoming line level signals exceed the input capability of the microphone input the DI box is feeding. Physically, the unit is simple but very rugged. The case is made from heavy square-section extruded aluminium and the sheet steel chassis containing the circuitry slides into this, where it is retained by six screws. The connector/switch panels are deeply recessed, making accidental damage unlikely.

Because of its high input impedance, the DI box is suitable for use with electric guitars and basses as well as general line sources. It appears to be tonally very neutral, as it should be, and is very quiet in operation. The additional security provided by true transformer isolation will be particularly appreciated in live applications. In all, a very well engineered and easy to use product, and though it costs a little more than a more run-of-the-mill unit, it should last a lifetime.

Further Information
Klark Teknik Active DI Box, £105.75 including VAT.

Klark Teknik plc, (Contact Details).