Amplifier Circuits: 
Low Noise Circuits

Composite Amplifier Improves Noise : 08/04/94 EDN-Design Ideas  

Low Noise Amplifier for Phase Noise Measurements: features less input noise than a 50 ohmresistor. 

Low Noise Balanced Microphone Preamp: very low noise, close to the theoretical minimum, high hum rejection and variable gain with a single rotary pot, similar to that used in many professional grade mixing desks

Low Noise Microphone Preamplifier:

Low Noise Variable Gain Amplifier: