saint gillis said:Ok, it's getting less foggy..
What about this 1:10 mic transformer (150:15k) : http://www.jensen-transformers.com/wp-content/uploads/2014/08/jt-115K-e1.pdf - the datasheet rates its input impedance 1.4K and its output impedance to 17K using a specific test circuit shown at the end of the doc, what are these values?
This example illustrates the struggle manufacturers have had figuring out the essential attributes to communicate to consumers (which may be product designers or regular end users) of these complex beasts. Historically, manufacturers just gave nominal impedance figures, and maybe frequency response (see old UTC or Triad catalogs for evidence). The nominal impedances didn’t reflect the actual impedances reflected by the transformer in circuit, but rather the source/output impedances of the devices connected to each side (in this case, a 150 ohm mic at the Input will reflect 17k to a FET or an input tube’s grid/grid leak resistor in the front end of a mic preamp -). This was supposed to help the consumer understand the proper application of the transformer.
Jensen here is taking the “newer” approach of specifying the impedances the transformer actually reflects in circuit. So this model will “show” a 1.4k impedance to a 150 ohm Mic when in the intended circuit, and 17k to the FET or tube. They tell you in the Datasheet both the connected device impedances and the reflected transformer impedances, and usually show a diagram of the test circuit. This is the approach Lundahl and maybe Cinemag take now (IIRC). More detail for a more educated end consumer.
BT