where there is a potential difference between the above mentioned base input terminals t b1 and t b2 the output current of each of the transistors q 1 and q 2 varies depending on its base potential however even in this case between the output currents i e 39 and i e 34 of the transistors q 1 and q 2 respectively a relationship i e 39 i e 34 i e is valid consequently they seasaw i e when one of them increases depending on the base potential the other decreases always according to this invention the circuit is operated under the condition that there exists a constant potential difference v b1 b2 between the base input terminals t b1 and t b2 so that the potential of the latter is lower than that of the former the working mode of the ac dc transformation circuit according to this invention will be explained below suppose that an ac input signal voltage v i as indicated in fig2 a is applied from the input terminal t i through c in acting as a coupling condenser and r in acting as a resistance for preventing electro static destruction to the base input terminal t b1 of the transistor q 1 in the above described differential amplifier and that the potential at the base input terminal t b2 of the transistor q 2 is kept at a potential which is lower b v b1 b2 than that of the former when no input signal is applied to the input terminal t i as the result an output current i e.