The plots appear to have a frequency point every 6 Hz. The noise is about -108 dBV at 1 kHz. Assuming the noise bandwidth to be 6 Hz, that's -115.8 dBV in 1 Hz, or 1.625 μV/√Hz. Divided by the gain of about 31.6 at 1 kHz, that's 51.4 nV/√Hz equivalent at the input, including the terms due to the amplifier's noise voltage and current and cartridge thermal noise. It is actually higher than I would expect.
I tried finding out about how Pico treats the FFT, and from their forum I read that indeed you can't use their FFT analysis for noise measurements. Apparently it's optimized for plotting spectrums of signals because they apply Coherent Gain to the window function. No idea what it means, other than I can only use the FFT to look at the level of the 50 Hz signal and the junk at the top-end. source: FFT analysis using Picoscope Anyhow, the SNR (apart from the 50 Hz hum and top-end junk?) is baked into the design, and is a given. I don't have any 100 Hz issues.
I will report back after running the pre-amp from 2 x 9V batteries.
When I look at the left parts of the plots, they look like collections of straight line segments between points that correspond to frequencies of 12 Hz, 18 Hz, 24 Hz and so on. Sometimes a line segment appears to span 12 Hz rather than 6 Hz, but that can mean that two adjacent line segments happen to have nearly the same slope.
That's absolute nonsense, but you have to know what you are doing.
Seeing spectral lines around 10Khz, doesn't sat they are indeed around 10Khz because you restricted the spectrum to 24kHz.
When using a much higher frequency range instead of 24Khz , these spectral lines won't fold back in the spectrum below 24Khz when indeed at a much higher frequency.
But you are so close to the Picoscope's own noise, that it would be wise to add another amp with at least 20dB gain behind your phono preamp and to measure behind this second amp.
Then use a much higher bandwidth like 100Khz and see where the peaks are now.
When magnifying the spectrum to the range up to 20Khz, you will get a true noise spectrum of your amp.
When knowing the frequency bin width, the noise per rtHz can be calculated and compared to the simulation.
Hans
P.S. Yes you have used a regulated PS, that would do in this case.
Is it safe to assume that the Picoscope is always sufficiently dithered by its own noise?
Was everything connected with 1:1 probes and/or coaxial cables or with 1:10 probes?
Was everything connected with 1:1 probes and/or coaxial cables or with 1:10 probes?
Quite. Measuring noise from an FFT is by far the best way to do it, but getting a correct result is not trivial.