sr555The SR555 and SR556 are ideal low‐noise current preamplifiers for SRS’ lock‐in amplifiers, and can also be used for any other small current detection purposes.SR555 Current Preamplifier. 10 VµA gain; 120 kHz (-3 dB) bandwidth; SR556 Current Preamplifier. 5 fA√Hz input noise; 1 VnA gain; SR556 Current Preamplifier. 5 fA√Hz input