Stereo Speaker RFI - elmers Forum at eHam.net

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Stereo Speaker RFI	Reply
by W7KPQ on February 25, 2007	Mail this to a friend!
What is the best way to get rid of RFI in stereo speakers. I've tried ferrite coils without any success. W7KPQ

RE: Stereo Speaker RFI	Reply
by KG4QPQ on February 25, 2007	Mail this to a friend!
Hi, Found this by doing a search on RFI in this very forum. Hope it helps. http://audiosystemsgroup.com/RFI-Ham.pdf 73 Louis

RE: Stereo Speaker RFI	Reply
by K6AER on February 25, 2007	Mail this to a friend!
You may have been using the wrong material ferrite. Use a number 43, 33 or 77 materials. If the RF is getting in on the speaker leads you will need up to ten turns around the ferrite core. RF can also come in on the feed lines from the DVD, VHS player and other audio sources. Also the AC leads can input RF energy. Each will need ferrite cores to prevent RF from getting into the amplifier. Depending of RF frequency you may need additional RF cores. The lower the frequency the harder it is to prevent RF on audio lines. What might work at 14 MHz will only be mildly effective at 4 MHz.

RE: Stereo Speaker RFI	Reply
by W5RB on February 25, 2007	Mail this to a friend!
.05 ufd disc capacitor (plus or minus a few hundred percent , the value's not critical ) across the speaker leads , as near the speaker as possible .This is easy , cheap , and the first thing I try .Usually fixes all but the worst cases . Russ , W5RB

RE: Stereo Speaker RFI	Reply
by K0BG on February 26, 2007	Mail this to a friend!
You want to be VERY careful about placing caps across speakers leads. Read the .pdf suggested above (http://audiosystemsgroup.com/RFI-Ham.pdf ) for further information. Alan, KØBG www.k0bg.com

RE: Stereo Speaker RFI	Reply
by W5RB on February 26, 2007	Mail this to a friend!
Somebody want to explain to me HOW a cap of this value could be a hazard , or function as anything except an RF bypass ? I skimmed the paper in question ( I'll read it at length later ) , and found no information that applies . Russ , W5RB

RE: Stereo Speaker RFI	Reply
by W7KPQ on February 26, 2007	Mail this to a friend!
I agree, I didn't see anything there either. Now tell me actually how to solder these in. I have a phono plug so I opend up the speaker and see where the wires attach but just not sure how to connect the .047 uf which I purhcased at RS. Richard W7KPQ

RE: Stereo Speaker RFI	Reply
by K8AC on February 26, 2007	Mail this to a friend!
Before getting too tied up in treating the speaker end of things, have you proven that the RF is getting in through the speaker leads? Any signal getting into the amplifier through any path will result in amplified noise in the speakers. If may very well be getting in through another path. You didn't describe the system, so it's difficult to suggest solutions. By the way, in my personal experience with such things, I've NEVER seen an instance where a bypass cap across the speaker did anything. I have had cases where the signal was entering via the speaker leads and in those cases winding the speaker leads on chokes at the amplifier end was effective. If we're talking a high-end system with hefty speaker cable, then clamp-on ferrites might be the best approach. Good luck with this.

RE: Stereo Speaker RFI	Reply
by KG6OMK on February 26, 2007	Mail this to a friend!
"Somebody want to explain to me HOW a cap of this value could be a hazard" Turns you AF amp into an ocilator if you are unlucky Look at the ARRL General license handbook. The one you read before the test. It there is is a section of RFI with a good fix for this exact problem. They use inductors in series with the cap. Inductors are home made with #16 wire over a 1/4 inch form. The inductor block the RF and the cap bypasses it.

RE: Stereo Speaker RFI	Reply
by K6AER on February 27, 2007	Mail this to a friend!
Placing a .047 uF cap across the amplifier output will not turn the output amplifier into an oscillator. The output impedance is between 4-8 ohms and the only effect of the capacitor would be to roll off the high frequency response of the speaker. Being we cannot hear above 20,000 Hz (young people) it is a moot point. The combinations of capacitance to frame ground and series ferrite cores will eliminate RFI from getting into the input amplifier and propagating through the amplifier chain and producing audio interference to the speakers. The RFI can inter via the audio input leads, speaker leads or even the AC leads. On the AC leads use ferrite cores only.

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