Originally Posted by
Barry
Yes your right. The actual voltage into the phonostage is lower than I stated, as I failed to take into account the modified source impedance as seen by the phonostage.
So to recap, the load as seen by the cartridge is (100 + 12470)/900 + 42.5 = 56.47Ohm. A potential divider is formed with the 3.5Ohm coil impedance of the cartridge, so the input to the primary of the SUT is 0.2 x 56.47/(56.47 + 3.5) = 0.188mV.
The source impedance as seen by the phonostage is (3.5 + 42.5) x 900 + 12,470 = 53,870 Ohm, and this forms a potential divider with the 100Ohm input impedance of the phonostage. So the voltage at the input of the phonostage is 0.188mV x 30 x 100/(100 + 53,870) = 0.01mV.
I can find no information for any small signal transformer marked as "T/5346/P" (either as an EMI manufactured device or as one made by Partridge (who use a similar designation system)), so cannot verify the values of the winding resistances; but they do seem high. However Martin reports that the SUT worked with his Denon 103 (0.4mV output with 40Ohm coil resistance) and now works with the correct input impedance setting on his phonostage, so the SUT would appear to be adequate for the job, if less than ideal.