[Elecraft] Audio Thump

[Vic Rosenthal]

Jimmy Lee wrote:

> Lyle and all others, I have done a poor job of explaining my problem.
> There is a low frequency sound just as the key is closed on ever
> single sound that is keyed.  Does not seem to be related to QSK. 
> Thanks, Jimmy

I have experienced this with some (not all headphones).  It is worse if 
for some reason you plug the 'phones into the external speaker jack 
instead of the headphone jack.

Also, I had a switching system which allowed me to switch the audio, 
keying, and antenna between my K2 and another rig; I found that when I 
used this, the thump was much worse!  I suspect that the cable to the 
'phones was close to the DC power cable of my K2/100 and the thump was 
actually induced in the 'phone cable by the large current in the power 
cable.

You can reduce the thump by putting a capacitor (I used back-to-back 4.7 
uf electrolytics) in series with the 'phones.  One pair of 'phones that 
I have requires this even when plugged directly into the headphone jack 
on the K2.

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco