[Boatanchors] 500 ohm vs. 600 0hm

[Stanley Adams]

Is historically embedded in the history of the separation of radio
broadcasting from those early pioneers in the telephone system, such as
Western Electric and others.
500 ohms was the accepted standard in all wire plants, and it came to be
that 600 ohms became important for the broadcasters.  In fact, the classic
dBm, is centered in 600 ohm history.

There are plenty of historical web sites that will speak to both impedances,
and the difference between them is not worth or hoot nor holler.  

If a device is marked either, then you assume that you either need to add a
transformer or one is built already into the equipment.  The circuit is
balanced in reference to ground, with both sides equal impedance from the
ground.   You can make a IC chip audio chip without using a transformer and
trick it to think that it is 600 ohms, but the actual impedance to ground
with any power out is closer to 20 ohms.  

Unbalanced circuits are of course 70 v usually, what we term as high
impedance consumer equipment 2-10K input and or output.  You can run a 10k
into a 600 ohm transformer but you really need to terminate the input with a
600 ohm resistor so that the high frequency content is not emphasized.


Stan Adams
Just my thoughts