Equivalent Input Noise
The amplifier’s noise expressed as the equivalent voltage at its input.
Input-referred noise accounts for amplification so that noise can be considered at the signal’s starting point. It is distinct from output noise or signal-to-noise ratio.
Equivalent Input Noise — MC Head Amp
For a Phono Head Amp, equivalent input noise helps assess the noise contribution when boosting a small moving-coil cartridge signal before an MM phono stage. Lower input-referred noise under comparable conditions means a smaller measured noise contribution.
Figures may use nanovolts, microvolts or a voltage-referenced decibel unit. Compare the stated bandwidth, weighting, source impedance and gain setting as well as the number. Changing these conditions can change the result without changing the amplifier.
A noise-density figure in nV/√Hz is not the same as a total noise voltage over a bandwidth. Do not compare it directly with an integrated noise figure. This measurement also does not predict hum from grounding or noise contributed by the rest of the system.