Low-noise audio amplifiers and preamplifier for use with intrinsic thermocouples

Two simple, low-noise audio amplifiers and one low-noise preamplifier for use with intrinsic thermocouples were designed, built, and tested. One amplifier uses ultralow-noise operational amplifiers; the other amplifier uses a hybrid component. The preamplifier uses ultralow-noise discrete components. The amplifiers' equivalent noise inputs, at maximum gain, are 4.09 nV and 50 nV; the preamplifier's input is 4.05 micro-V. Their bandwidths are 15,600 Hz, 550 Hz, and 174 kHz, respectively. The amplifiers' equivalent noise inputs were measured from approximately 0 to 100 Hz, whereas the preamplifier's equivalent noise input was measured from approximately 0 to 174 kHz.