[Elecraft] K3 external speakers

[Sam Morgan]

I use a pair of amplified Labtec computer speakers
with my K3's rear Stereo speaker output
I like the ability to either listen on headphones and speakers
or turn down the speakers and have a quieter room using the cans

although I did have some rfi initially
it was getting in from the little wall wart power supply for the speakers
a simple fix was 8-9 wraps of the power cord where it entered the speaker
around a small yellow toroid salvaged from a dead computer supply

later I upped my power to 400w with an AL-811
and and the rfi from the speakers was back
this time I did a 6 turn wrap
through one of the square snapon toroids
this was placed on the line coming from the K3 to the speaker input
at the end right next to where it entered the amplified speaker

all I'm saying is don't just throw out the idea of using
a set of cheap computer speakers you may have around the shack
it may be a really simple fix to get the going.


GB & 73
K5OAI
Sam Morgan

On 12/21/2010 6:24 PM, Jim Brown wrote:
> On 12/21/2010 10:11 AM, George A. Thornton wrote:
>> Amplified computer speakers have been a problem for me.  They are not
>> well screened for RF and on occasion I have had bad feedback problems.
>
> Yes, amplified loudspeakers (that is, speakers with built-in amplifiers)
> are notorious for serious RFI problems, thanks to poor shielding, poor
> circuit board layout, poor input filtering, and Pin One Problems.  I
> work in the world of pro audio, and take a VHF/UHF talkie with me to
> trade shows to test for RFI immunity in various products. Over a period
> of about ten years,  I've seen only a couple of RFI-proof loudspeakers,
> and they were in the $3K range. And I've seen lots of loudspeakers in
> that range (or even higher) with nasty RFI problems. :)
>
> The loudspeaker output stages in the K3 are sufficient to drive an
> external passive (unamplified) loudspeaker of reasonable efficiency to a
> more than enough level for those who aren't seriously hearing impaired.
>     A number to look for in loudspeaker specs is 85dBSPL or more for 1
> watt at one meter into 8 ohms.  Most of us would set a loudspeaker
> within 20 inches or so, which increases the level by 6dB, and, as I
> recall, the K3 has a 1 watt output stage. That puts a peak loudness of
> 91 dB in our ear for CW, and about 10dB less for SSB.
>
> 73, Jim Brown K9YC
> ______________________________________________________________