Ultra-Low-Noise Amplifiers and Granularity Distortion
It has often been speculated in hi-fi publicatiaons that passive components such as capacitors and connectors may exhibit threshold or "granularity" effects, analogous to power-amplifier crossover distortion, that become audibly significant at low signal levels despite an ability to detect them with conventional instrumentation. An ultra-low-noise emplifier system of high linearity is described, which allows low-impedance passive components to be tested for nonlinear distortion or threshold effects at extremely low signal levels. Total harmonic distortion at the 0.01% level is detectable for a test signal level of 200 µV. The application of similar circuit techniques to the design of moving-coil head amplifiers of high quality is also described. No evidence of granularity was found in any of the components tested at low levels.
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