[Elecraft] K3 "hum" problem - not the usual?

[Joe Planisky]

Would wrapping some of this "Ultraperm 80" shielding around the K3's  
audio transformers be a solution?

(http://www.goldmine-elec-products.com/prodinfo.asp?number=G16600A)

73
--
Joe KB8AP


On Sep 28, 2009, at 12:06 PM, Jim Brown wrote:

> On Mon, 28 Sep 2009 13:29:54 -0400, Brian Machesney wrote:
>
>> The problem only occurs in an
>> SSB mode when the nearby PA is both on and enabled (i.e., not on  
>> "standby")
>> and when the K3 is both within about 8-in of the PA and parallel or  
>> at right
>> angles to it; rotating the rig about 15 degrees around the z-axis  
>> eliminated
>> the hum. All in the usual vein, so far.
>
> Magnetic field coupling from the power supply to the K3's input  
> circuitry,
> probably due to the use of unshielded audio transformers in the K3.  
> This is a
> well known problem. One good band-aid is to go to the TXEQ1 settings  
> and fully
> cut the three lowest octave bands. There's little communications  
> value to the
> speech below 300 Hz anyway, and it burns TX power, so it's a win- 
> win. Also,
> the acoustic stuff in that lower frequency range includes breath  
> pops and room
> noise.
>
> It's also possible to have magnetic coupling on input wiring if  
> you've managed
> to form it into a big loop, but the transformers are the more likely  
> cause. I
> ran into the loop problem once when I jury-rigged a headphone amp  
> for SO2R. No
> problem in TX audio, but it was in my phones. One of my neighbors  
> had so much
> magnetically coupled hum into the Line In transformer that it  
> regenerated to
> full output power when he tried to run RTTY in AFSK mode.
>
> 73,
>
> Jim Brown K9YC
>
>
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