You can lower the load impedance by adding a resistor (in fact two: remember, stereo!) between the + and the – of the RCA plug (out of the step-up).
Suppose you have a 1:10 gain step-up. Your actual load impedance is 470 ohms (natural impedance). You would like to test a load impedance of 100 ohms. Let’s now calculate the value of the resistors you should add:
In fact, by adding resistors, you’re modifying the impedance of the MM entry (actually equal to 47 000 ohms - standard). To have a load impedance of 100 ohms, you need to have an MM entry impedance of 10 000 ohms (remember 10000/10^2=100).
First thing to do is to calculate the desired impedance for your MM input before calculating the value of the resistors you’ll need. Use this formula:
Wanted_IMP = (xgain)^2*(wanted_load_imp)
Now to calculate the value of the two resistors you need in our case:
Rload = 1/(1/10000-1/47000) = 12.7 Kohms
Generally: Rload = 1/(1/R1 – 1/R2)
Where: R1 is the impedance you want for your MM input and R2 is the actual impedance of your MM input
以上、引用終わり。
Allen Bradley のカーボン抵抗（12.9k/26.5k）が手元にあったので使用。負荷抵抗は、それぞれ40Ωと60Ωになります。
話を戻すと、昇圧トランスの設定に関して「Step-Ups and MC Cartridges | The Secrets of a Successful Marriage」と題した資料が、参考になりました。DL-103にPeerless 4629 を当てた際、各一次インピーダンスにおける出力電圧および負荷抵抗が下表。（二次インピーダンスは70kΩに固定）
