I'm new to Step Up Transformers

I am constantly surprised when others report they hear important differences between two different load resistances, using LOMC or LOMI cartridges, that are numerically very close to each other on a scale of 100 to 47K ohms. Like 725 vs 525 ohms or 800 vs 1000 ohms. I believe the reports because they’re subjective, but I’m surprised anyway; I don’t hear important differences between such values. In fact I think of loading in terms of logarithmic differences. So i might try 100, 1000, maybe 10,000 ohms and then 47K ohms. If the cartridge permits that array of load Rs, I choose one among them but usually the difference in sonics is not dramatic. Atmasphere points out that one is actually loading the phono stage. Maybe my array of phono stages is less sensitive than some others. One thing I would not do is choose a load resistance lower than recommended. Notice that no maker sets an upper limit on load R. None say not to use 47K ohms.

lewn,

I agree with you.  The higher the number the LOWER the loading.  At low value of resistors (meaning a lot of loading) small numerical changes do matter a lot (like 30 ohms and 50 ohms are quite different), but, once one gets above 150 ohms, there already isn't much loading and it should not matter that much.  The only thing that does matter is where RFI is interfering and overloading the phonostage.  In that case, a small amount of loading may be needed to cure that problem and this should not affect the overall sound.  A friend suffered RFI that we traced to the default setting on his phonostage being 100kohms (essentially no loading); when we went with 1kohm loading, the problem went away.

On many cartridges, I prefer a lower level of loading (high value resistor)  than most people choose for their setup.  This delivers a wide open sound.  Jonathan Carr, the designer of Lyra cartridges said that modern MC cartridges do not need additional loading to tame high frequency resonant peaks because those peaks are primarily in the ultrasonic range.  When loading does improve the sound, it is because those ultrasonic peaks can overload phonostages that don't have enough margins for peak levels.  I don't have that issue myself, probably because my phono stage is a tube unit that doesn't have extended ultrasonic frequency response.

I did not try the lower of the gain settings on the MC channel because I assumed that it would be too low.  But I guess it's as easy as flicking a switch to see what happens.  

  I should have thought of that. Duhhh

@rmcfee SUTs require proper care and feeding if you want the best out of them.

Transformers transform impedance. So the output impedance is a function of the turns ratio and the source impedance (the cartridge and cables).

If the SUT is insufficiently loaded (load value too high) it will overshoot (ring), which is saying it will make distortion and be bright. If the load is too much (too low an impedance) the transformer will roll off highs. There is an exact value that is called 'critical damping'.

The cartridge itself doesn't care about the loading until the load is very close to the impedance of the cartridge. So your main concern is making sure the transformer is properly loaded (critically damped) so it will sound right. The correct value (which may be a simple resistance or might be a resistance and capacitance in series) varies with the cartridge and to a smaller extent, the tonearm cable.

This is why I prefer a phono section that has enough gain so I don't have to use an SUT; loading SUTs correctly is tricky and beyond the abilities of most audiophiles. I posted the procedure on a different thread recently.

(To take some of the guess work out of this Jensen Transformers has a pdf file that lists all the cartridges they've encountered for use with their SUTs. Unless your phono section uses a Jensen (which would be a good move as Jensens are some of the best available) that pdf doesn't apply to your situation.)

If you don't use the procedure the result is very much like building a loudspeaker from scratch without knowing anything about speaker design. It will certainly play, but sounding right (being neutral) will be up to chance.

Thanks so much Atmasphere. The Zestos has Jensens (I'm told) in the MC channels. That's great info about SUTs.