SUTs and Resistive Loading Questions

Al, you are correct. I need to take into account the SUT with a 100 ohms setting on my phono preamp. But if you run the calculations as if loading on the secondary side, doesnt look like I will be able to do it - Id have to increase load, and that is a lot harder.

But if you run the calculations as if loading on the secondary side, the SUT’s affect is negligible.

I’m still not following you. If a 15:1 SUT is inserted between the cartridge and a 100 ohm phono stage input the cartridge will see a load of 0.4 ohms. (Approximately, that is, because additional effects such as DC resistance will become significant under such an extreme condition). And that would amount to putting a near short across the output of the cartridge, and would pretty much kill the signal it is trying to put out.

Regards,
-- Al

You are correct.  I fixed my prior post before your last response.

If you must use a SUT, you can either place a ~200R resistor on the primary side and no added resistance on the secondary side (47K only) or a ~43K resistor on the secondary side of the SUT, in parallel with 47K, to achieve a net 100R load.  However, I am puzzled when you say your phono stage affords the built-in option of 100R; that implies to me that it must have gain sufficient for at least some low output MC cartridges, in which case you might not need a SUT. Because 100R is not a load value one associates with high output, i.e., MM/MI cartridges.

But like Almarg says, you don't want to use BOTH the 100R setting AND the 1:15 SUT.

Dear @edwyun : "  In a prior setup, I did notice a difference between 100 versus 200 or 470 ohms ....Cart is Dyna 20x2L. "

The didifferences because loading is not much because the cartridge " reaction " tha's almost no sensitive to normal load changes. Those differences comes from the phono stage " reaction " to those loading changes.

Anyway,  you will follow making load changes till you are where you like it more.

Regards and enjoy the music,
R.