1. A trifferential amplifier system comprising: an amplifier having three amplifier inputs and three amplifier outputs; three voltage input terminals for receiving three input voltages and being interconnected with said amplifier inputs through three input impedances, respectively; and a feedback network including three summing circuits for combining said three amplifier voltage outputs in three different sets of pairs, respectively, and feeding back the sum of each pair of amplifier voltage outputs to the remaining amplifier input for maintaining the voltage difference between any pair of amplifier voltage outputs proportional to the voltage difference of a corresponding pair of input voltages at said terminals and maintaining the average value of the amplifier voltage outputs constant and unrelated to the input voltages at said terminal.