Why Phono Stage Hiss?

So, did anybody see his "deliberate" mistake?

If 1k has noise voltage of 4nV then 100k is 100 times 4 = 400, not 40.

However, it serves the purpose of informing us what the input noise is.

Now, in a real amplifier the input isn't grounded like what's shown in the video - it has a source, and that source has impedance, and that impedance is its driving impedance (not to be confused with recommended load impedance).

The video looked at fixed resistors, but impedances are AC resistances which appear in sources and might not look like fixed resistors, but are there nonetheless.

An MM cartridge is roughly 1k at 1kHz and some as high as 3k. Therefore we can add 4 to 12 nV of noise to the input. The phono stage might have 1k of series resistance with its input prior to its "load capacitor" to aid radio rejection - that adds another 4 nV.

At 20kHz a MM cartridge impedance is closer to its matching impedance (47k) and so, as a source, it becomes noisier; but because of the spectral spread (the frequency response) being "corrected" by the RIAA EQ, the noise doesn't rise rapidly at high frequencies.

It is because of the EQ that multiplying out the noise voltages by the square root of bandwidth (20kHz being 141) does not give us the correct noise answer.

So does more gain equate to more noise? In one way it obviously does, but then in another it doesn't. It will obviously be dictated by the noise of the source, and if that source's impedance is substantially lower, then a higher gain might not lead to more noise.

We can see in the Accession specifications that the difference between MM and MC versions is only 1dB, yet the MC has 20dB more gain.