The model 1212 current preamplifier is designed as a low cost, general purpose benchtop instrument that provides 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 rolloff due to input cables and stray capacitance. The zero input impedance also allows photodiode detectors to operate linearly over a very wide dynamic range.
Like the model 564, it is optimized to have the widest bandwidth consistent with standard lock-ins, yet not be overpeaked when operated with moderate capacitance tranducers, 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.