The SSM2018T and SSM2118T represent continuing evolution of the Frey Operational Voltage Controlled Element (OVCE) topology that permits flexibility in the design of high performance volume control systems. Voltage (SSM2018T) and differential current (SSM2118T) output versions are offered, both laser-trimmed for gain core symmetry and offset. As a result, the SSM2018T is the first professional audio quality VCA to offer trimless operation. The SSM2118T is ideal for low noise summing in large VCA based systems. Due to careful gain core layout, the SSM2018T/SSM2118T combine the low noise of Class AB topologies with the low distortion of Class A circuits to offer an unprecedented level of sonic transparency. Additional features include differential inputs, a 140 dB gain range, and a high impedance control port. The SSM2018T provides an internal current-to-voltage converter; thus no external active components are required. The SSM2118T has fully differential current outputs that permit high noise-immunity summing of multiple channels.