The Model 1212 current preamplifier is designed as a low cost, general purpose, bench top instrument to provide a high performance detection system for small ac and dc currents. The 1212 operates with a virtual ground at its input which mitigates unpredictable high frequency roll off due to input cables and stray capacitance. The zero input impedance also allows photodiode detectors to operate linearly over a very wide dynamic range and photomultiplier tubes to operate with minimal distortion.

It is optimized to have the widest bandwidth consistent with standard lock-ins, yet not be over peaked when operated with moderate capacitance transducers such as small area PIN photodiodes. Models 1211 and 1641, by comparison, are more highly damped, and work with higher capacitance input devices. The 1212 is switchable for operation directly from an ac power line or from internal, sealed, lead-acid,rechargeable batteries.