Posted by
Ron D'Eau Claire-2 on
Jul 02, 2004; 11:01pm
URL: http://elecraft.85.s1.nabble.com/OT-Line-level-tp368401p368416.html
I did work on some audio systems - half a century ago - so I'm no expert. We
did use 600 ohm "line level" output for long distance lines (e.g. from a
microphone mixer just off stage to the power amplifiers up in the projection
booth in theatres). That might involve 200 or 300 feet of cable by the time
the got from one place to another. The connection was made with a shielded
and balanced line with - and this I assumed was the critical part in the 600
ohm specification - a 600 ohm center-tapped transformer at each end to
suppress common-mode noise the line might pick up.
I thought it was interesting that Elecraft resurrected this application
specifically to avoid noise pickup by the circuit traces within the K2
carrying audio. That's why the K2 has a fully balanced audio system until
the signal gets to the LM-386 output I.C. The problem there isn't external
noise, it's the abundant digital noise floating around inside the K2 that
can easily get into the low-level audio lines.
Ron AC7AC
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