API Audio 3124V, 4-Channel Microphone, Instrument and Line Preamplifier, Classic API circuit design, API 2520 OP amplifier, Switchable 3:1 Output transformer for each channel, Switchable 48 V Phantom Power, -20 dB pad and polarity for each channel, LED Meter as well as adjustable gain and output volume for each channel, 4 XLR Inputs, 4 Hi-Z Inputs: 6.3 mm Jack, 4 XLR Outputs, Design: 19"" / 1 U