Abstract: A transformerless bidirectional amplifier useful in a balanced two wire to single wire line circuit, which blocks common mode signals and allows full control of signal levels, impedances, etc. A differential amplifier circuit is connected to the balanced wires, and has its output connected through a buffer amplifier to a single unbalanced wire. A second differential amplifier has its respective input terminals connected to the input and output of the buffer amplifier. The output of the second differential amplifier is connected to one of the balanced wires, and through a resistor to one of the inputs of the first differential amplifier which is connected to the other of the two balanced wires. The value of the latter resistor is such as to apply sufficient output signal from the second differential amplifier to the first differential amplifier so as to cancel a signal from the second differential amplifier which is applied to the first differential amplifier via the first wire of the balanced pair.