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:[email protected] > > 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:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
