internal signal routing2-channel/4-channel input switch - routes RCA input from channels 1/2 to channels 3/4.When the switch is engaged, channel 1 input isrouted to both amplifier channels 1 and 3 withinput channel 2 routed to amplifier channels 2and 4.Switch in the engaged position.When the switch is disengaged, channels 1, 2,3, and 4 receive signal individually from theirrespective inputs.Switch in the disengaged position.Level controls - Independent level controls for channels 1/2 and 3/4 adjust the inputsensitivity from 100 mV to 8 VRMS.Output - Three position switches determine the output configuration. Each stereo pair of channels canbe configured in either stereo, summed-bridged and bridged-mono.When the switch is in the left position, the output channels are configuredfor stereo operation.When the switch is in the center position, the output channels are configured forsummed mono bridged operation by mixing the left and right input signals together.When the switch is in the right position, the output channels are configuredfor a bridged mono output using a single RCA input. Ch 1 input is used forchannels 1 & 2 and ch 4 input is used for channels 3 & 4.15