The model 99539 is a modular, multi-channel current preamplifier with parallel, logic level gain control input. It consists of circuit boards that plug into a 3 1/2 inch high by 19 inch wide rack chassis. Each board comprises a single preamplifier channel. Each board includes a front panel with controls to manually override the remote gain control inputs. The front panel also contains indication light emitting diodes. The 19 inch rack chassis accommodates eight preamplifier channels. It also has a ninth slot for a user-provided microprocessor, which provides gain control outputs, digitizes the preamplifier outputs, and communicates via the VME bus to other system components. The 19 inch rack chassis incorporates a regulated dc supply that provides power to all nine modules and detector bias potentials.