The UNiKA SDI-2 is an easy-to-use, dual-channel, passive direct box for musical instrument and audio system applications. In addition to a high-quality audio transformer, the SDI-2 has some very useful built-in features.
There are 2 channels on the SDI-2, each featuring an XLR- ¼“TRS combo jack INPUT, a TS ¼“ parallel LINK output and a balanced XLR OUTPUT. Connect your source instrument or audio device to the input and the balanced XLR output to the mixing console. The LINK connector output provides the means for connecting the signal to an instrument amplifier or personal monitor system. Unbalanced cables are much more susceptible to noise than their balanced counterparts. Keeping unbalanced cables under 8 meters (25 feet) in length is good practice while balanced cables can easily extend to 100 meters (300 feet). The balanced output of the SDI-2 is mic level, meaning that it should be connected to the mic input of a mixing console or mic preamp.
INPUT PAD ATTENUATION
The most common use of the direct input is with guitar pick-ups, keyboards or audio devices like CD players, computers etc. The optimal setting for this is most likely with the pad switch set to 0dB, although with some high-output pick-ups the performance of the direct input may be improved if the pad switch is set to -20dB to prevent possible clipping of the input signal.
The instrument is connected to the XLR-¼“Combo jack socket using a TS jack plug, and a parallel link feed taken from the LINK TRS jack socket to the instrument amplifier. The direct input can also be fed either from a line-level output from the head-amp (pad set to -20dB) or from the head-amp speaker output ( pad set to -40dB).
The PAD setting applies to both inputs.
ELIMINATING HUM AND BUZZ AND THE GROUND LOOP
The SDI-2 is equipped with output isolation transformers to eliminate hum and buzz caused by stray DC voltage and ground loops. Computers, CD players and other consumer equipment can be noisy – this is particularly true when incorporating audio with a projector – so isolation transformers can be very useful when combating system noise.
The independent Ground Lift switches on the outputs takes this one step further by lifting pin-1 on the XLR. Computers are often the source for noise problems in audio systems, so greater care is certainly needed to keep things quiet.