Phono preamp or SUT for low output moving coil

@herman

I really appreciate your contributions here. They provide good information on SUT’s designs and careful selection of SUT’s for anyone looking to pursue this route. 

I believe you’re right, the EMIA’s design with a higher input impedance makes it particularly well-suited for low-output moving coil (LOMC) cartridges that benefit from higher loading impedance. The standard 47kΩ load, a legacy from the moving magnet (MM) era, often results in suboptimal performance for MC cartridges, which typically need more tailored loading for the best sonic results.

If I interpret correctly what you said, using a step-up transformer (SUT) with a high-impedance load like 300kΩ opens up much more flexibility. The higher impedance allows for better cartridge damping and less tonal constriction, especially with LOMCs that thrive in the 500–1,000Ω range. The example of a 1:20 ratio yielding 750Ω into 300kΩ is a great illustration of how dramatically this can improve compatibility compared to the more restrictive 118Ω with the standard 47kΩ.

Loading the primary to fine-tune impedance is another clever technique, and Dave Slagle’s calculator is an excellent resource for those looking to experiment.

There is a direct mathematical correlation, in fact. And the more voltage gain afforded by a SUT, the lower the impedance seen by the cartridge, which will be the input impedance of the phono stage (usually 47K ohms) divided by the square of the turns ratio (which is synonymous with voltage gain).

@lewm  is absolutely correct. My SUT allows both 15:1 and 10:1 turns ratios, and therefore allows a 47kΩ MM input to be seen as either 208Ω or 470Ω. It makes a difference!

Actually, you can change the load resistor in any MM stage to whatever value you prefer, if you can identify it and can solder.

I wouldn’t go so far as to say "any" since the input impedance may be determined by more than a single resistor, but it is certainly the most common way. Hopefully whoever is in there replacing  resistors knows enough to determine what is needed.

The caveat with going too far is that increasing the input impedance also increases the amount of noise that gets in, so there is a practical limit

I agree with most of what has been discussed, but would like to point out that there is no conflict between the use of an SUT and choosing a phono stage that has an accurate RIAA curve.  I guarantee that the the use of the two together can be serendipitous.

The question or the argument is how accurate is accurate enough?