600ohms still seems to be the practice for ship and aircraft intercoms that
I've come across recently.
David
G3UNA
Yes. 600 ohms has not been part of audio practice, pro or consumer, for at
least 40 years. ALL line level and mic level audio circuits, pro and
consumer, are low impedance source, high impedance termination. The signal
is transferred as a voltage, not as power or current. Typical output
impedances are on the order of 100 ohms, input impedances are typically
10K for pro line level, 50K for consumer line level. 100 ohms is chosen
primarily because it is a good value for isolation of op amps from the
capacitance of the cable that it drives. This capacitance can be
significant in pro installations, but rarely in consumer applications.
>
For those who are interested, there's more on this in the tutorials on my
website. http://audiosystemsgroup.com/publish
73,
Jim Brown K9YC
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