[Elecraft] High pitched hum after installing KXBC3?

[Jessie Oberreuter]

      I finally had the chance to put my KX3 together over the weekend! 
Yay!  I don't know if it's the same thing you're hearing, but there is a 
high pitched whine in the audio on my unit (it transfers from the speaker 
to the headphones when they're plugged in).  Sounds like a G/G# ... maybe 
something in the 12.8 khz range?  I don't have access to anything right 
now that can actually measure it.
      The volume of the tone doesn't change with AF gain -- tho what AF 
Gain mean in this radio is non-obvious :).  It also doesn't change with 
band or mode, nor with a change of power supply (three different external 
supplies), nor location, nor presence or absence of antenna.  I have the 
ATU and filter, no battery charger.
      I can easily hear it using the internal speaker, but I'm hoping I can 
fix that with a judiciously chosen capacitor across the speaker leads.  I 
essentially can't hear it on my Heil cans, so I'll be fine this Field Day, 
but it turns up clearly on ear buds, so I'd like to fix that side as well. 
I don't recall having heard it on anyone else's KX3, but stuff in this 
range is pretty easy to either miss or misattribute unless you have good 
high frequency hearing and you're by yourself in a quiet room, and it 
could also vary from unit to unit.  Finally, I won't claim to be pitch 
accurate up there, but until I can measure it on something, a good guess 
is better than nothing :).

-kb7psg

On Fri, 2 Nov 2012, David F. Reed wrote:

> I notice a high pitched hum (low level) when my KX3 is on, after
> installing the KXBC3; has anyone else noticed this?
>
> What might be causing it?  Is it possible to eliminate?
>
> Other than the hum, everything seems to be normal and working fine.
>
> Thanks and 73 de Dave, W5SV