Behringer Ultra-DI 100 An active design drawing power either from an internal 9 volt battery or via phantom powering. Response 10Hz - 50kHz. Input fully isolated with a transformer. Very quiet front end preamplifier includes gold plated XLRs and jacks for inputs and outputs. A 50dB switched input attenuator allows connection directly to instruments, line level signals or speakers. An Earth lift switch provides isolation against hum loops. Corners are protected by rubber bumpers which also allow multiple units to be stacked vertically.