[Elecraft] K3 Hum on Audio...

Lew Phelps K6LMP k6lmp at me.com
Thu Feb 2 13:24:07 EST 2012


Thank you, Tony!

I had developed a maddening audio hum suddenly, and couldn't find the cause.  The curious thing was that it was WORSE when no mike was plugged into the jack on the back panel.

Based on your email, I checked the menu settings. Sure enough, MIC + LINE:  ON.  Switched to OFF and the hum totally disappeared. You don't need to adjust the LIN volume; just cut it off entirely.

Lew K6LMP


On Jan 14, 2012, at 9:02 AM, N2TK, Tony wrote:

> Make sure the LIN IN is not turned up. Early on I had a problem with hum in
> my audio, especially if an amp was close to the K3. For some reason my LIN
> IN was at max. Turned it down and hum went away.
> 73,
> N2TK, Tony
> 
> -----Original Message-----
> From: elecraft-bounces at mailman.qth.net
> [mailto:elecraft-bounces at mailman.qth.net] On Behalf Of Phil Hystad
> Sent: Friday, January 13, 2012 12:54 PM
> To: jim at audiosystemsgroup.com
> Cc: elecraft at mailman.qth.net
> Subject: Re: [Elecraft] K3 Hum on Audio...
> 
> Jim,
> 
> Well, I would call it mostly a buzz.  Also, the only near magnetic field of
> the KPA500 power transformer is off, I mean powered off and unplugged, so
> that does not seem to be the problem.
> 
> I just ran another test with everything disconnected, including ground and
> coax.  With the K3 in TEST mode, key-down on the mic still produces the hum.
> I double checked the grounds.  I did this because if I were to touch
> anything metal on the k3, the metal part of the PL259 or the ground strap,
> the hum is damped quite a bit to almost insignificant.  It seems that if my
> rig were already well grounded this would not happen so I am curious if this
> is something I would normally expect.
> 
> I will experiment with the TXEQ but this is a real puzzle I would like to
> solve, not merely erase it.  
> 
> 73, phil
> 
> 
> On Jan 13, 2012, at 9:37 AM, Jim Brown wrote:
> 
>> On 1/13/2012 9:20 AM, Phil Hystad wrote:
>>> Unfortunately, it is in both mics but not as strong in the Yamaha CM500
> mic as in the MH2 but it is present.
>> 
>> Clarification question.  Is it HUM (pure 60 Hz), or BUZZ (mostly 
>> harmonics of 60 Hz)?  If it's HUM, I would suspect magnetic field 
>> coupling into the audio, either from a big power transformer (like the 
>> one in a power amp or a big linear power supply) or from a AC power 
>> wiring fault called a double-bonded neutral.
>> 
>> The K3 has unshielded audio transformers at all the audio inputs and 
>> outputs, and an unshielded transformer is a sitting duck for magnetic 
>> fields.
>> 
>> The good news is that the K3 has excellent audio equalization (TXEQ) 
>> that allows us to remove that 60 Hz hum by filtering.  The lower audio 
>> frequencies in the human voice make NO useful contribution to speech 
>> intelligibility, but they do waste transmit power. So it is ALWAYS a 
>> good thing to set the TXEQ for maximum cut of the lowest two bands, 
>> and at least some cut of the third band. This is true with virtually 
>> ALL mics and ALL voices.  AND it will reduce that hum enough that you 
>> may no longer hear it.
>> 
>> There are several solutions to magnetic field coupling.  1) Rotate the 
>> noise source or the victim circuit to put the fields at right angles 
>> to the victim.  2) Move the noise source further from the victim. 3) 
>> If the hum field is produced by that AC power wiring error, fix the 
>> error to eliminate the field.
>> 
>> 73, Jim K9YC
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:Elecraft at mailman.qth.net
>> 
>> This list hosted by: http://www.qsl.net Please help support this email 
>> list: http://www.qsl.net/donate.html
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> 
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html



More information about the Elecraft mailing list