Tube DIY Asylum: MC step up transformer math check by jsn

Ok, so I have been on a quest for a great and inexpensive moving coil stepup transformer (and mic input transformer) and while trying to "do the math" on various winding ratios, I have run across some discrepancies. I am used to simply multiplying the input voltage times the winding ratio to get the output voltage - but when the impedance that the cartridge sees is not much larger than its own output impedance, that falls apart.

I think this is the right equation. Please check my work :)

Vout = Voltage at phono pre = Turns Ratio * Coil Voltage Output * (Load Impedance / (Load Impedance + Coil Impedance))

If this is right, it definitely explains why so many people like the Altec 4722 which appears to have a way-too-high winding ratio.

Also, to be even more correct that usual :) the impedance calculations should take into account not just the reflected impedance, but the DC Resistance of the windings as well. Here is the math from the K&K audio spreadsheet, which I believe is correct:

Rload = Load Impedance = ((phono input impedance + SUT secondary resistance) / (Turns Ratio^2)) + SUT primary resistance

Thanks,
jsn