[Elecraft] K3 speaker audio gone!

[Mike Goldstein]

         I've lost audio from both the internal speaker in the K3, 
and from the SPKRS output jack on the rear panel.

         At the end of the the first week of using a new NESCAF audio 
filter (which drives my speaker) with the K3,  I changed bands, 
listened briefly on CW, with the NESCAF filter in the circuit.  I 
then changed to SSB, and because the NESCAF filter was adjusted for a 
very narrow audio bandwidth, I decided to switch it out of the 
circuit, while the K3 was delivering audio, at a comfortable listening level..

         The audio filter was driven from the SPKRS jack on the back 
of the K3, using a stereo plug, with one channel floating.  The SPKRS 
jack was CONFIGured as SPKRS = 1.

A front panel toggle switch on the filter panel turns off the power 
to the NESCAF filter, and re-routes the speaker audio connection from 
the filter output, to the K3 output directly. I had done this often, 
for the first week of operations.

This time, however, I briefly saw a "HI CURR" indication on the front 
panel of the K3, and then my speaker audio vanished.

Unplugging all connections from the rear panel SPKRS jack, and the 
front panel PHONES jack, no longer allows the K3's internal speaker 
to produce audio.  Nothing I tried would result in any audio from the 
external speaker, after connecting that speaker to either of the 
phono jacks that were tied to the rear SPKRS jack, through the stereo plug.

The INPUT jack on the SCAF filter (to which the K3's SPKRS jack was 
connected) passes through an isolating capacitor, then a 27K 
resistor, before being connected to the chip in the audio filter.

Resetting SPRKS = 2, in the  CONFIG menu, had no effect on producing 
audio in the external, or internal speaker.

I still have audio  at the PHONES jack on the front panel, so I can 
still use the K3.  It subsequently accounted for 380 QSOs in the NAQP 
CW contest, providing it usual flawless performance.

I still have audio at the PHONES jack on the rear panel, as well.

My theory (and Gary at Elecraft Service agrees it might be the cause) 
is that the audio chip in the K3 didn't like the abrupt change of 
load impedance, from 27K (approx.) to infinity, to 8 ohms, while it 
was delivering audio..

I've since soldered a 15K resistor across the input jack of the audio 
filter, and will do likewise for any other audio filters I encounter, and use.

Puzzling, huh?