On Mon,12/28/2015 11:57 AM, Steve Ellington wrote:
No problem...Just grossly out of specs.
Steve,
You clearly don't understand what you're reading on that data sheet, nor
the design of audio output stages. I refer you to my earlier posts, and
to those by W4TV, W2RU, and W3FPR.
Those numbers you quote are NOT the output impedance, they are the
minimum LOAD impedance that the output device is designed to work into.
Modern output stages are essentially constant voltage sources. That's
what Bud is telling you with his discussion about damping factor -- the
output Z (source Z) is typically 50-100 times the load Z.
With headphone amplifiers, a good designer will add some small value of
resistance in series with the output to prevent the output stage from
failing if a short is connected to its output (which could occur when a
plug is being inserted, or with an improperly wired plug). Line level
outputs use a series output resistor to prevent the output stage from
seeing the CAPACITANCE of a long cable, which could, by interaction with
the feedback network, cause the output stage to oscillate.
Executive summary -- simply buy good quality headphones, and don't worry
about impedance.
73, Jim K9YC
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