I've completed a series of detailed measurements trying to understand
why my K3's LIN OUT port exhibits greater distortion and anomalies than
found in the headphone and speaker ports.
Details are at
http://www.cliftonlaboratories.com/elecraft_k3_receive_audio.htm
What I found is that the 604 ohm resistor between U29's output amplifier
stage and the TTC-108 transformer primary winding forces the TTC-108
isolation transformer to operate in a regime where the performance
improving effects of a zero ohm driving source are not available. Hence,
the TTC-108's 0.5% THD performance significantly limits the LIN OUT
ports performance.
I've also provided a theoretical parts value change that should improve
the LIN OUT distortion and intermodulation. I have not implemented this
change in my K3, but the external circuit mockup I used for testing
strongly supports the change.
I've supplied my measurements to the gurus at Elecraft for their
consideration. If my data and recommendations make sense, I would
expect confirmation from Aptos, after they have time to think it over
and consider possible side effects.
Jack K8ZOA
www.cliftonlaboratories.com
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