Playing with Cartirdge loading on my phono stage

The manufacturers usually know their own products best. I always stick with their recommendation. You will not notice much when you play around.

Which means that you can take some bigs steps.
If they say 50-200 ohms, then you could try 40 or 50 and 1k to bound the problem… If you cannot hear much change from that, then just stay at 200.

Or try 50, 100 and 200 and see if there is much in it.

No. The reason the sound changes is due to distortion- LOMC cartridges and the tonearm cable together form an electrical resonance that generates Radio Frequency Interference which is injected directly into the phono section and can cause distortion. The loading resistor detunes the electrical resonance, thus eliminating the RFI.

However if your preamp was designed by someone that knows about this phenomena, you'll find that the highest load impedance (47,000 Ohms) is the right one, with little or no effect at lower resistances other than the tracking ability is reduced.

@atmasphere does that mean we can just select the load with an o-scope?
and select the highest resistant value possible?

It would be better to use a distortion analyzer, but this would only be of benefit if the phono section can't deal with the RFI on its own. If the phono section does deal with the RFI properly, you'll see no benefit from the loading in terms of distortion.

@atmasphere thanks Ralph - what would the distortion look like? IMD, noise, or HD.

I am guessing it might look like IMD beating an RF tone against the audio signal??

Asking because I can digitise the TT signal, and look at it spectrally and do some math on it. Just need to know what to look for… (Like everything other than the specific test record tone freq?)

Thanks @atmasphere - Ralph you are a gentleman, and your thoughts, and guidance, are very much appreciated.