[Elecraft] K3 speaker audio gone!

[Dave Hachadorian]

I have blown the speaker amp twice, in two different radios, by 
using a speaker with AGC OFF.  POOF! Gone before you can react by 
turning down the audio.

The factory guys report that they have been unable to duplicate 
the problem.  Unless you are an EXPERT solderer, replacing the 
speaker amp chip is best done by the factory.  The job will run 
about $125 with shipping, maybe a little less if you ship only 
the DSP Board.  I don't use the speaker amp any more.  I still 
think there is a transient susceptibility problem in that 
circuitry that they have been unable to find.


Dave Hachadorian, K6LL
Big Bear Lake, California






-----Original Message----- 
From: Mike Goldstein
Sent: Tuesday, August 28, 2012 9:07 AM
To: elecraft at mailman.qth.net
Subject: [Elecraft] K3 speaker audio gone!

         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?  73 de  VE3GFN
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