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 <d...@nk7z.net> 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 <d...@nk7z.net> 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:Elecraft@mailman.qth.net > >> > >> This list hosted by: http://www.qsl.net > >> Please help support this email list: http://www.qsl.net/donate.html > >> Message delivered to n...@n6ol.us > >> > > > > > ______________________________________________________________ > 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 > Message delivered to n...@n6ol.us > -- *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:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
