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Old 17th August 2013, 11:04 PM   #11
Pano is offline Pano  United States
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Quote:
Originally Posted by JonSnell Electronic View Post
I can't think of an amplifier with RFI in the loudspeaker connections.
I'm listening to one right now! I own several others.


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Old 17th August 2013, 11:12 PM   #12
jcx is offline jcx  United States
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from next door in an apartment building power line conducted noise is possible too - mains filtering may help
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Old 18th August 2013, 03:46 AM   #13
brig001 is offline brig001  United Kingdom
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Yes, you are right and a friend has just pointed out that it's likely to be the lift (elevator), so just going to filter everything.
Thanks,
Brian
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Old 18th August 2013, 11:35 PM   #14
Lavcat is offline Lavcat  United States
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I once had a problem with RFI from the other side. My six meter transmissions were causing interference to someone's hi-fi. Never did solve it.

These days my speaker cables run near AC cords, computers, and SCR's but I don't have any interference problems that I know of. (There was a shortwave station in my phono stage that turned out to be caused by a Monster interconnect.)

Would there be audible benefit to adding ferrites all over everything? I'm sure there is a lot of RFI floating around here. But I don't think I can hear or taste or smell it.

I became a believer in ferrites when a company I worked for had to add ferrites on our products' cables to meet FCC certification.
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Old 19th August 2013, 12:10 AM   #15
Pano is offline Pano  United States
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Because RF was coming out the cables?
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Old 19th August 2013, 12:43 AM   #16
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I used to have a neighbor with a boosted-up CB radio. I'd be rudely awoken by his trucker voice blasting from my speakers every morning. (even if the stereo was off.) Ferrite,small bypass caps,shielded cables,different amps,more grounds,nothing fixed it. Luckily I wasn't the only one he annoyed,cause a couple weeks later they were gone,I suspect evicted.

I like the clip-on ferrite beads,and tend to use them a lot.Great for power cords,and other various cables. They're handy RFI stoppers,I at least kinda try to quench RFI/EMI,if I can.
(Trying to listen to a shortwave radio/scanner with a PC nearby is a mess of whistles,and 'ghost carriers',for example.)
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Old 19th August 2013, 10:56 PM   #17
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Quote:
Originally Posted by Pano View Post
Because RF was coming out the cables?
Yes.
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Old 19th August 2013, 11:03 PM   #18
Lavcat is offline Lavcat  United States
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Quote:
Originally Posted by DigitalJunkie View Post
I used to have a neighbor with a boosted-up CB radio. I'd be rudely awoken by his trucker voice blasting from my speakers every morning. (even if the stereo was off.) Ferrite,small bypass caps,shielded cables,different amps,more grounds,nothing fixed it. Luckily I wasn't the only one he annoyed,cause a couple weeks later they were gone,I suspect evicted.
One can be punished for that, at least in the US. The FCC would propose a non-technical solution.
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Old 20th August 2013, 12:29 AM   #19
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Neville Thiele (of T/S fame) designed a LCR network for the output of a power amp' which, when connected to a speaker of appropriate impedance, increases amp' stability and also acts as an RFI filter for noise picked up by the speaker leads. I will try and describe it. Assume 8 ohms. There is a parallel LR network of 2mH and 8ohm in series with the output. Then instead of the classic 8R and small cap' in series from the hot (speaker end of the LC network) to the ground he just has a small cap'. About 0.1uF I recall. Looks odd but when the speaker is connected (i.e. across the cap') it forms an parallel RC network and all things being equal the amp then "sees" an 8 ohm resistance and any RFI picked up by the leads experiences a 6db/oct attenuation before getting to the output terminals.
The first version used on some local DIY magazine kits from the mid '70s was the basic version which gave a 6db/octave roll off. But if you chase up the JAES paper there are two further iterations of 2nd and 3rd order networks (more complicated and elegant) for very severe cases of interference. Can't think of the actual year and volume reference right now.............
actually it is; JAES 1976 24(1) pp 20-23.
Cheers,
Jonathan
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Last edited by Jonathan Bright; 20th August 2013 at 12:38 AM. Reason: Found the reference
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Old 24th August 2013, 01:27 PM   #20
Magz is offline Magz  United States
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I've found from experience that adding ferrites to a signal line is not to my tastes; it always seems to change the sound in a direction I don't like.

I did however, DIY some RC speaker cable filters that are still in place. Once installed at both the amp and speaker end of the wire they seemed to me to have a very positive effect on the sound. Whether they are filtering out RF or simply terminating the TL more effectively, I don't know, but they do something I like. I calculated the characteristic impedance of the speaker wires at RF and chose the resistor value to match that. The caps are cascaded silver micas. Before potting I embedded the caps in mortite to attempt to damp resonances. Inside the potting box is an inner box of TI-shield material.

Here are a few pics showing what I did. The final filters are potted in epoxy and as hard as bricks.
Attached Images
File Type: jpg RC Filter Project 001.jpg (24.8 KB, 109 views)
File Type: jpg RC Filter Project.jpg (23.1 KB, 109 views)
File Type: jpg RC Filter Project 003.jpg (24.0 KB, 109 views)
File Type: jpg RC Filters Potted.jpg (28.6 KB, 109 views)
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