13 April 19

In every amplifier circuit, the input resistor is critical. Any noise at the input signal will be amplified to the full gain. It is therefore of high importance to choose a low-noise resistor at the first stage, as well as a low resistance value. This is however not valid for a load resistor, since the gain that is obtained from a high resistance value outweighs the higher noise level. Because thermal noise is temperature dependent, it is very effective to cool the input stages to reach a low-noise performance.

Noise is an unwanted phenomenon for resistors. For some applications the noise properties are important. Examples are high gain amplifiers, charge amplifiers and low-level signals. Resistor noise is often specified as micro-volt, noise per volt of applied voltage, for a 1 MHz bandwidth. Thermal noise is the predominant source of noise for resistors.  It is dependent on three variables: resistance, temperature and bandwidth.

Read more http://www.resistorguide.com/resistor-noise/