I bought several of these miniature audio transformers from Electronic Goldmine. They are encapsulated so I can’t see anything, windings, core or materials. There are 5 pins, 2 on one side and 3 on the other, but the center pin measured open, so it’s apparently there to make sure the transformer is inserted the right way.
The ad says 0.45 henry per winding, and both windings are the same so the turns ratio is 1 to 1. My tester says both of the windings measure 1.44 henry, so I’m not sure what the exact value is. I’m going to measure it with another meter to see.
From what I can guesstimate judging by other known audio transformers, this one should have an impedance of around 2000 to 6000 ohms. The windings are slightly different DC resistance but that’s because the inner winding has less circumference per turn than the outer winding – even though both windings have the same number of turns. The wire length is slightly shorter and slightly less resistance.
I’m curious as to how they determined that these transformers are audio. They could be for pulse generation and have a ferrite core for frequencies in the tens to hundred kilohertz range. At those frequencies the winding impedances would be high. My thoughts are that this transformer might be used to isolate the powerline side of a SMPS from the low voltage and controller side. This is usually done with an optoisolator, but a transformer can also be used.
I’m wondering if it would be worth opening one up to see what’s inside. I used a propane torch to reclaim the toroid cores from potted transformers, I just burned away the plastic until a core with charcoal and wire was left. I don’t know if the core on this audio transformer is ferrite or laminations, but it’s very small and light, so laminations would be very tiny and light.