must be an error, load impedance guidance: probably 100 ohms, not 10.

gain and load are inverse. high gain/low load. low gain/high load

yours is a difficult combination of very low signal strength and 8 ohm resistance.

an X Factor of 25 would boost 0.16mv to 4.0mv, I like that.

X factor 25 squared = 625. 47000 / 625 = 75 ohm load, a bit low ....

X factor 20 boost’s 0.16mv to 3.2mv weaker than I would want.

x factor 20 squared = 400. 47000 / 400 = 118 ohm load, good.

don’t forget, there is a slight loss of signal strength, i.e. calculated 4.0mv might actually be 3.8mv; 3.2mv might actually be 3.0mv, just guessing here.

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solution: for cartridges with these difficult relationships: a phono stage with separate gain choices and separate load choices. opens up the choices to nearly anything. they get expensive.

Or, change to a cartridge with more compatible relationship, in your case, lower impedance, or higher output.