The Pendulum Instruments Dual Channel High Voltage Linear Amplifier A400DI contains two independent A400 amplifiers that share common ground reference and power supply. It features also a low voltage phase inverter that inverts the signal applied to the input of channel 1. The resulting signal can then be connected to the input of channel 2 by means of a short BNC cable (supplied). As a result the two outputs operate in counter-phase. Connecting a load between the outputs effectively doubles the amplitude range. Please note that the load cannot have any connection to ground. Also, in order to see the signal over the load you must use two oscilloscope probes and use the math function.