[Elecraft] K3 speaker audio gone!

[hawley, charles j jr]

Actually kind of scary about that choice of chip. There must be something more robust since we have numerous audio devices around that last when abused.

Sent from my iPhone

On Aug 28, 2012, at 11:14 AM, "Mike Goldstein" <mgold at pathcom.com> wrote:

>         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? 
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