The SUT provides 12dB voltage gain, so the 3.5mV output of your SPU is transformed to 14mV, which will overload an MM input. I'm not surprised you are having problems.
The SUT provides 12dB voltage gain, so the 3.5mV output of your SPU is transformed to 14mV, which will overload an MM input. I'm not surprised you are having problems.
Barry