[Elecraft] KX2 speaker/headphone question

[Jim Brown]

On Mon,2/6/2017 6:35 PM, Don Wilhelm wrote:
> One of your big problems is that the speaker specified in that project 
> is 8 ohms - if you can find a 4 ohm speaker, you will almost quadruple 
> the available audio. 

Not quite. A loudspeaker amplifier is essentially a constant voltage 
source. If the two speakers have the same efficiency, the 4 ohm speaker 
will be 3 dB louder. But all speakers do NOT have the same efficiency, 
and Elecraft has been good at choosing small speakers with high 
efficiency for their size.

That speaker in QST is a cute idea and demonstrates the principle of an 
acoustic filter. That's the value of it.

The KX2 and KX3 are carefully designed to maximize battery life for 
portable operation. Part of that careful design is to limit the current 
in the audio output stage. It's really designed for headphones, or with 
external amplified loudspeakers.

BTW -- I think the original question about the output being "padded" is 
a reference to a passive attenuator -- a resistive voltage divider. In 
the audio and broadcast world, components or networks like this are 
called a "pad."

No, the output of these radios are not padded in that sense, but it is 
good practice to add a small resistor in series with the output of any 
audio power amp that connects to a jack, so that it's less likely to be 
damaged when a jack is partially inserted and shorts the output. :)

73, Jim K9YC