On March 21, 2006 at 17:33, Ernie Bornn-Gilman said...
A nominally
500 ohm transformer with a turns ratio of 1:1,
connected to an amp with a 10K ohms input impedance
will look like 10K!
True. A transformer does not just transform voltages, but impedances as well. The impedance presented at the output stage of the transformer is reflected back into the input, but will vary with the turns ratio.
One of the issues is that the baluns being used don't usually have 1:1 turns ratios. The baluns are usually designed for CAT5 or 6 UTP cable. The baluns are designed to provide correct termination impedance at both ends of the cable. If they didn't, as the length of the cable went up, you'd start to have problems with reflections.
You can get away with using less than the absolute best choice under many circumstances. If the cable lenths are of medium length. If the audio run is analog rather than digital. (Here the Common Mode rejection ratio offered by the cable and the baluns is likely of more importance than the impedance.)
