Propeller Head Plaza

Technical and scientific discussion of amps, cables and other topics.

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This is correct

Posted by Triode_Kingdom on August 19, 2021 at 14:09:04:
I'm retired now, but my day job for many years consisted of design and measurement of low phase noise circuity in the region of -180 dBC. This doesn't correlate directly with amplitude noise, but the worst-case equivalent is orders of magnitude better than any vacuum tube. Our products approached the theoretical limits of physics in this regard, and all used thin film resistors. Leaded components aren't usually marked thin or thick film, but resistors like those sold by Vishay with tempcos around 250 ppm/K are undoubtedly thin film. When resistors of this type are used, the noise floor of active devices generally proves to be the limiting factor.
Edit: Just to add some relevance to this, most of our products were RF-related. However, we did sell an opamp-based audio amplifier with an input referred noise of <1 nV/√Hz, and our proprietary in-house design using discrete components was very close to 0.5 nV/√Hz. Both products used standard thin film chip resistors.