The UNiKA SDI-1 is an easy-to-use, single-channel, passive direct box for musical instrument and audio system applications. In addition to a high-quality audio transformer, the SDI-1 has some very useful built-in features.
Ground lift switch acting on pin-1 of the balanced output.
Instrument Direct input & Parallel Link connection
There is one channel on the SDI-1, featuring an XLR- ¼"TRS Combo jack INPUT, a ¼" TS parallel LINK output and a balanced XLR OUTPUT.
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 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 SDI-1 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 Ground Lift switch on the output 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.