Josephson transmission structures (JTSs) which include Josephson transmission lines (JTLs) with filter circuitry and flux release circuitry. Two or more of these JTSs may be interconnected to form a superconducting high-gain operational amplifier intended for general-purpose analog signal processing is disclosed. The active elements of the amplifier are non-hysteretic Josephson junctions configured as dc SQUIDs (used as flux-to voltage transducers and impedance transformers) and Josephson transmission lines (used as the main source of power gain). The amplifier has inverting and non-inverting voltage inputs, which can be fed from any low-resistance low-voltage sources, including dc SQUIDs. The output of the amplifier is in the form of a voltage which can drive typical transmission line impedances (e.g., 10-100 ohms). The variety of possible sources of input signals and the high gain of the amplifier enables wide range of applications including linear signal amplifiers, integrators, active filters and phase-locked oscillators.