All of Jim's material is like gold for RFI suppression.
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources
On 5/23/20 2:02 PM, Nicklas Johnson wrote:
Thanks, Dave. A very good point about the amp picking up stray RF off
the cable and returning it as audio; I'll be sure to clamp down on both
ends.
It's definitely not a new problem, and I've used Jim's recommendations
to much success in the past. In fact, I referenced it again today
because I couldn't remember which mix of Fair-Rite was the right one.
Nick
On Sat, 23 May 2020 at 10:58, Dave Cole <[email protected]
<mailto:[email protected]>> wrote:
I would put the ferrite material as close to the speaker as possible,
and as close as possible to the amp...
It is important you also protect the amp from stray RF. If the speaker
cable is picking up RF, and feeding it back into the audio amp output
stage, you can get rectification within that stage in the amp, thus
feeding actual audio, (not RF), back down the speaker cable into the
speaker(s), and then you start hearing things on the speaker(s).
I had a ham friend living 700 or 800 feet from me-- when he lit off his
KW, I would hear SSB in the speakers, even with the amp off, and
unplugged. This was happening via the method above.
See Jim's paper on quieting things down:
http://www.audiosystemsgroup.com/RFI-Ham.pdf
73, and thanks,
Dave (NK7Z)
https://www.nk7z.net
ARRL Volunteer Examiner
ARRL Technical Specialist
ARRL Asst. Director, NW Division, Technical Resources
On 5/23/20 10:19 AM, Nicklas Johnson wrote:
> I've got a set of these on the way, as well as a handful of their
next two
> smaller siblings, just because I like to have a variety in my
desk for
> various applications:
> https://www.fair-rite.com/product/round-cable-snap-its-2631181381/
>
> Given the arrangement at the subwoofer of wall-connection-->isolation
> transformers-->subwoofer, would you put the ferrite right before the
> subwoofer then?
>
> I didn't think about adding one at the amp; though I haven't had
problems
> with any common mode noise getting into the amp from the other
speakers in
> the room, I can't be sure about the LFE coaxial cable, so that
wouldn't
> hurt.
>
> Nick
>
>
> On Sat, 23 May 2020 at 10:08, Dave Cole <[email protected]
<mailto:[email protected]>> wrote:
>
>> Grab some FT-240/31 ferrites from Fair-Rite, (these are the large
>> rings), and put seven or eight turns of speaker cable through each,
>> tight wound. Add one at the speaker, and one at the amp.
>>
>> 73, and thanks,
>> Dave (NK7Z)
>> https://www.nk7z.net
>> ARRL Volunteer Examiner
>> ARRL Technical Specialist
>> ARRL Asst. Director, NW Division, Technical Resources
>>
>> On 5/23/20 9:37 AM, Nicklas Johnson wrote:
>>> The backstory as briefly as I can make it: I wanted to place my
home
>>> theater subwoofer in the corner of our living room; doing so
required
>>> running two speaker wires and a coaxial cable under the house and
>> plugging
>>> the subwoofer into a different outlet than the AV receiver;
this in turn
>>> resulted in ground-loop hum (because of a tiny difference in
potential
>>> between the two outlets) which I worked around with a set of 1:1
>>> low-frequency audio isolation transformers. The subwoofer is
of a type
>>> that produces a signal based not only on the LFE channel, but
also on the
>>> left and right speaker channels, thus the two speaker wires
along with
>> the
>>> coaxial cable.
>>>
>>> Now the subwoofer is picking up common mode noise on 20m, which
isn't
>>> terribly surprising, as this happens a good bit with consumer-grade
>>> electronics. I'm hoping to mitigate this with some substantial
ferrite
>>> clamps for all three connections and as many turns as I can get
through
>>> them.
>>>
>>> My hunch is that the best place in the path to clamp them on
will be
>>> immediately before the connection to the speaker itself, on the
speaker
>>> side of the isolation transformer, but I wanted to get the
opinions of
>>> folks who have solved this problem in the past to see if
there's any
>> reason
>>> the ferrites should come before the isolation transformers.
>>>
>>> Thoughts?
>>>
>>> Nick
>>>
>> ______________________________________________________________
>> Elecraft mailing list
>> Home: http://mailman.qth.net/mailman/listinfo/elecraft
>> Help: http://mailman.qth.net/mmfaq.htm
>> Post: mailto:[email protected]
<mailto:[email protected]>
>>
>> This list hosted by: http://www.qsl.net
>> Please help support this email list: http://www.qsl.net/donate.html
>> Message delivered to [email protected] <mailto:[email protected]>
>>
>
>
______________________________________________________________
Elecraft mailing list
Home: http://mailman.qth.net/mailman/listinfo/elecraft
Help: http://mailman.qth.net/mmfaq.htm
Post: mailto:[email protected] <mailto:[email protected]>
This list hosted by: http://www.qsl.net
Please help support this email list: http://www.qsl.net/donate.html
Message delivered to [email protected] <mailto:[email protected]>
--
*N6OL*
Saying something doesn't make it true. Belief in something doesn't make
it real. And if you have to lie to support a position, that position is
not worth supporting.
______________________________________________________________
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
Message delivered to [email protected]
