Two simple, low-noise audio amplifiers and one low-noise preamplifier for use with intrinsic thermocouples were designed, built, and tested. The amplifiers and the preamplifier have different front end designs. 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 nV. Their bandwidths are 15 600 Hz, 550 Hz, and 174 kHz, respectively. The amplifiers' equivalent noise inputs were measured from ~0 to 100 Hz, whereas the preamplifier's equivalent noise input was measured from ~0 to 174 kHz.

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