I certainly agree. And of course there's no "one size fits all" for RFI problems. I think it's somewhat likely I have multiple problems going on here too; I noticed, for example, that even when it's completely disconnected from all its audio inputs, I can still hear a little racket on the sub; it may need a hefty ferrite on the power cord, or I suppose it's always possible it's picking up 20m from the speaker coil, then rectifying that. I won't know until I get some appropriate ferrites delivered to test out (mid-week).
Sadly, it seems like most consumer-grade audio equipment is optimized more for cost than for design quality and RFI suppression, even equipment that's supposed to be "high-end." And then sometimes you can buy a piece of cheap gear and it rejects RF better than high-end stuff. Kind of a crap shoot. I appreciate all the suggestions and pointers. In the absolute worst case, I can always play on another band when my better half wants to watch a movie or play a game, too. Nick On Sat, 23 May 2020 at 16:39, Dave Cole <[email protected]> wrote: > 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. > -- *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]
