Very low noise cooled audiofrequency preamplifier for gravitational research

Abstract

We describe a low-frequency amplifier whose front end, realized with field effect transistors, is cooled at the temperature of 150 K. The results of the measurement of the noise voltage and of the noise current are given as a function of both frequency and temperature. The amplifier has an optimum noise temperature of 25 mK at 1.8 kHz with a source resistance of 390 kΩ and has been used in connection with a gravitational wave antenna of the Rome group.