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-boun...@mailman.qth.net [mailto:elecraft-boun...@mailman.qth.net] On Behalf Of Phil Hystad Sent: Friday, January 13, 2012 12:54 PM To: j...@audiosystemsgroup.com Cc: elecraft@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@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@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@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
