[Elecraft] K2 s/n 5361 SSB TX audio problem

[ON4WIX]

Hi John (and all at the reflector)

Thanks for your answer.
I just grounded the mic jack housing following the guidelines I found on the 
Elecraft web site.
No improvement however. I have tried different compressor settings (and 
bypassing it) but this does not improve or worsen the audio.
When I hold the microphone about 1 foot from my mouth the audio seems OK but 
of course I'm not putting much power out. Moving the mike closer to my mouth 
the choppiness quickly becomes apparent. When I press my lips against the 
mike it sounds slightly better although rather distorted, a bit like the 
famous recording of the first man on the moon "A small step for man but a 
giant leap for mankind".
I carried out my test on 40m. The thing that struck me also was that I got 
very little ALC reading, only 1 bar lighting up occasionally. That one LED 
didn't flicker along the rhythm of my modulation either. It just flickered 
on and off in a quick fashion and stayed lit for about half a second after I 
stopped talking.
I recorded my test a few minutes ago. If anyone wants to listen to this 
recording in order to assess the problem, please drop me a mail and I'll 
send the file.

Have a nice Sunday

73 de Glenn ON4WIX

----- Original Message ----- 
From: "John D'Ausilio" <jdausilio at gmail.com>
To: "ON4WIX" <on4wix at skynet.be>
Sent: Sunday, April 09, 2006 5:41 AM
Subject: Re: [Elecraft] K2 s/n 5361 SSB TX audio problem


>I had a crappy audio issue that turned out to be RF getting into the
> audio .. there's some docs around that describe how to correctly
> ground the housing of the mic connector, you might want to try those.
>
> gl de w1rt/john
>
> On 4/8/06, ON4WIX <on4wix at skynet.be> wrote:
>> Hi all
>>
>> I'm experiencing a funny problem with my K2 s/n 5361.
>> My KSB2 board went through intitial testing without problems, all 
>> measured values were OK as per the manual.
>> My TX audio however is horrible. It sounds very choppy (one ham reported 
>> to me it sounds 'very restrained'), it seems like the signal is cutting 
>> out and then switching back on in a very rapid fashion. I get almost no 
>> ALC reading when modulating, neither speaking very closely into the 
>> microphone nor a few inches away.
>> At first I thought I was experiencing the well-documented low mike gain 
>> problem. When speaking very closely to the microphone (a Kenwood MC43) 
>> the audio sounds reasonably clear (distorted but not much gets chopped 
>> out) but as soon as I move away from the microphone the chopping effect 
>> kicks in. This led me to believe that my mike output level was too low 
>> and that the KSB2's noise gate was operating on its gating threshold.
>> I then connected a preamp between the mike and the K2. With the K2 
>> connected to a dummy load I listened to my TX signal through my Kenwood 
>> TS570. Varying the preamp gain made no noticeable difference, the audio 
>> kept sounding distorted.
>> I then tried the R14 mod (changing the 1k R14 into a 10k resistor). No 
>> solution, still very crappy audio (I disconnected my preamp at this 
>> stage).
>> At that moment I discovered a funny thing: when speaking into the mike at 
>> a distance of approximately 1 foot I noticed that my audio was almost 
>> sounding natural. Of course I was not getting any power out of the K2 
>> this way. When I moved the mike closer to my mouth the distortion quickly 
>> came back.
>> So, at this moment it looks like I'm grossly overmodulating when I speak 
>> at a normal distance from my mike. It sounds a lot better when I speak 
>> far away from the mike but then I'm really running QRPp, hi.
>> I've taken the KSB2 board out of the K2 and checked all soldering joints 
>> (which seem OK). One of T2's leads looked suspicious so I desoldered T2 
>> and rewound it with the little spare wire I had left and resoldered it. 
>> Still no luck.
>> Receive audio is OK so the filters seem do be doing fine.
>>
>> Any suggestions on where to start looking for the cause of this problem 
>> are more than welcome.
>>
>> Thanks in advance
>>
>> Glenn ON4WIX
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>
>