I have that transformer here and haven't had time to test it yet.
In the datasheet they loaded the secondary with 11k, source of 50ohms.
That is clearly not the way it is supposed to operate, which suggests they have chosen a setup that provides better figures.
I thought ~11k would be used for 150ohm source but just a wild guess.
11k at the secondary reflects as 150 ohms at the primary, which is not correct for customary n1:10 bridging. that would be correct for 1:1 matching, though.
edit. Looking at some Cinemag mic input transformer documentation and some mic preamp circuits I see they have a RC snubber circuit in parallel with the RL of 150K, source of 150ohm.
That is quite usual; said Zobel circuit linearizes the HF impedance without loading at LF and MF.
The voltage gain measurement in the OEP datasheet for the A187A15C transformer is at 150ohm source, 150K RL. [/quote] That is more in line with typical usage; the reflected input impedance then is about 1.5k, which is adequate for 1:10 bridging.
But it shows that the specsheet is a tad devious, because if the gain measurement was done with the previous setup (50ohms source, 11k load, the gain would be only about 12dB.
Adam
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