[Elecraft] Low headphone audio level and a question to Wayne

[Lyle Johnson]

>> What are the headphone output impedances of the front panel and the rear
>> panel jacks and do they vary between modes?.

The LM4811 headphone amplifier provides maximum power transfer into a 16 
ohm load (105 mW), and 70mW into a 32 ohm load.  Ifas you increase th 
eload impedance, the headphone driver becomes voltage limited.  If you 
reduce th eimpedance too much, it will become current limited.  There 
are 8.2 ohm resistors in series with left and right channel outputs of 
the LM4811 and the front panel headphone jack, and another pair of 8.2 
ohm resistors in series from the LM4811 to the rear panel headphone 
jack.  The resistors protect the headphone amplifier from short 
circuits, nd also reduce the effect of reduced output in one set of 
headphones if another set is plugged into the other headphone jack.

73,

Lyle KK7P