I just spotted this in the online archive which wasn't emailed to me. I
apologize in a advance for others who post replies without getting a
response from me. If the list server doesn't send me a copy, I may not
spot it in the archive. The original message is at the bottom. First is
my reply: 

Hi Walter, 

Thanks for your feedback. I appreciate it. Yes, I'm aware of that
amplifier. It would be appropriate for driving bookshelf HiFi speakers,
as your writeup demonstrates - cool project, by the way. Aside from 15W
being overkill for driving the 2W/3W driver in the SPX3, it wouldn't fit
in the enclosure, and would need to be modified by hand to work as
needed even if it did fit. Most transceiver external speakers put out
2-3W, as that's all that's necessary for listening to voice and CW at
close range. Plus, when taking the SPX3 portable, it needs to last a
long time on a battery. 15W per channel (30W) would drain a battery
mighty quick. I turned the prototype on this morning when I got up, and
it's still running after more than 15 hours on the same battery charge. 

The SPX3 sports features specific to what the KX3 needs, such as a low
pass filter, built-in battery and charging circuitry, a shielded
enclosure to eliminate RF from the antenna affecting the audio, works
great outdoors, the speaker cone won't get damaged if it gets wet, and
more. Plus, it matches the KX3 and supports KX panels and covers
(already in talks with the SIDE KX folks). You might want a pair
yourself to take on the road. 

Thanks and 73,
Robert (AG6ZZ) 


Walter Underwood [1] Fri, 13 Apr 2018 11:58:12 -0700 [2] 

I use this 12 V audio amp. It would be easy to put it inside a speaker.
seems to vary in price a bit. Today it is $8.50, on the low side.

"DROK TDA7297 15W+15W Audio Power Amplifier Module AC/DC 9-18V 2.0 Dual
Stereo Amp Board"

At home, I stick it to the top of one of the speakers with velcro.
Writeup is 


Walter Underwood
http://observer.wunderwood.org/ (my blog)


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