[Elecraft] K3 Hum on Audio...

[Ron D'Eau Claire]

Wow - this is strange! 

1) Are all the K3's enclosure screws tight? Have you tried tapping or
lifting the K3 while listening to the hum (looking for an intermittent
connection)? 

2) Does the hum remain if you key the rig in CW mode?

2) If you move the K3 and battery supply to a different location (room
perhaps) does the hum remain?

Your needing to cut up to 400 Hz is not surprising. It's not unusual for 60
Hz hum to have a number of harmonics if the waveform is getting distorted in
the process of being picked up.

The fact that it's being picked up with AC disconnected to everything in the
room suggests that it's a fairly high-level high-impedance circuit picking
it up. Such circuits can pick up 60/120 Hz buzz from many blocks or miles
around. 

BTW, I can't imagine how an external ground would have an effect with
nothing connected to the K3, but if you're thinking of checking outside,
now's the time. I see we're due for snow at low elevations in the Northwest
by tomorrow night. 

Ron AC7AC

-----Original Message-----

As noted in a previous post, I disconnected EVERYTHING.  Nothing on the back
panel of the K3 at all except for a Li-nano-phosphate battery as my power
source.  All AC off at the breaker panel for this room.  The only electrical
equipment on was my K3 via the battery and my Macbook Pro laptop via its
battery.

Given those conditions, the hum was still there.

Jim Brown suggested that I consider TXEQ to cut off the low frequencies,  I
did max cut for all frequencies up to 400 Hz.  The hum did not start being
attenuated until 400 Hz cut.  But, max cut on 400 Hz did not attenuate it
completely.  I did not do higher frequencies.

So, anyone who might help -- where does this hum or buzz come from if
nothing is connected to the K3 and there is no AC flowing anywhere in the
room.  It is 28 degrees outside, which is freezing cold plus for the
northwest and I am not used to that but my next step is to go outside and
check my grounding to ground points.

phil