Calculation verification please

I refuse to read the gibberish, but if you place a 51K resistor in parallel with a 47K resistor, you will get around 24K resistance. If you use your 1:40 SUT into 24K resistance, you will end up with a phono load of about 15 ohms. In other words, you’re going backwards. I don’t care what the book said. But your cartridge can drive even 15 ohms. So if you do the 51K mod, it will work ok, but the load is not 375 ohms. The only way to increase the resistance of a resistor is to place another resistor in series with that resistor, and obviously you don’t want to do that in this case.

just for the fun of it, if you have an ohm meter, and if you have two 50 K resistors, place them in parallel and measure the resistance across the parallel pair. It will be 25K ohms.

what you could do is replace the 47K load resistance with a 600K load resistor. Then using your 1:40 SUT, the cartridge will see 375 ohms load.

Agree, which is why I titled the thread "Calculation verification please" The answer ChatGPT gave didn’t make sense to me. (and yes a lot of gibberish but fasinating to watch it do the calculations in a matter of seconds).

I can’t replace the 47K load resistor but also came up with a 600K load resistor answer.

I must have misunderstood from the get go. I thought your original question was what parallel loading resistors would create a 375 ohm load.  Answer is still that it's not possible by introducing a resistor in parallel with 47K. I personally would do nothing; just run the cartridge into the 30 ohm load.  On the other hand, I don't know why you cannot change the load resistor from 47K to 600K, but I take your word for it. I don't think there would be anything magical about 375 ohms anyway.

@sksos1 The cartridge won't care about the 375 Ohm load. It won't care about 30 Ohms either.

Loads like that are never for the cartridge's benefit; they are to eliminate RFI (Radio Frequency Interference) that LOMC cartridges tend to generate. The resistor detunes the electrical peak (which is usually at some radio frequency) thus preventing it from going into oscillation.

The SUT prevents this problem of course since it lacks the bandwidth, so it blocks RFI.

In addition to what I and Atma have written, I am most amazed that you hear differences in SQ among resistances of 250, 324, 368, 404, 500 & 600 ohms. I don't doubt you, but I have tried such experiments and never heard much if any difference.  Or to put it another way, if there IS a difference among such closely related values, it is so subtle as to be irrelevant.  I set up one of my phono stages to be switchable between 100, 1000, and 47K ohms for LOMC cartridges.  Now I do hear slight differences between 100 and 47K ohms, but both are acceptable and close to being the same.  If I had to say, I would say 47K is slightly more tipped up toward the treble.  This is with cartridges that have internal resistance between 2 and 12 ohms. This phono stage is balanced and the cartridges are hooked up on balanced mode always, straight through to the speakers. (Balanced phono, linestage, and amplifiers.) Speakers are full range ESLs.