BALanced-to-UNBALanced. A transformer device used to convert a singled-ended (unbalanced) signal to a differential (balanced) signal. A bal-unbal is essentially a transformer with one leg of the input and output windings hooked together. More complicated devices may also change impendences at the same time. The most common use for a bal-unbal is a 75 ohms coaxial-300 ohms twin-lead converter used in television.