Amp picks up local radio - Page 2 - AVS Forum
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post #31 of 50 Old 03-08-2012, 08:54 AM
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Quote:


read back

I did.

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Any unshielded wire can be an antenna. But when in use as a speaker cable, it doesn't transmit those signals anywhere due to the high current energy traveling through it.

No, still not convinced.
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post #32 of 50 Old 03-08-2012, 12:42 PM
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Originally Posted by Theonetruegreg View Post

Excellent work on your ability to copy and paste from another source.
Reading is an important life skill.

Did this paper also go on to say that the speaker wires that are cryogenically treated and blessed by saints are even better at resisting interferrence?

Are you purposely trying to come across as a dolt? The paper is about ferrite cores being used as low-pass filter to remove radio frequency interference...nothing magical there bud.

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Originally Posted by Theonetruegreg View Post

I have never seen any speaker wire in a properly designed and working system introduce audible noise, have you?

Once again, the "wire" is not the source of the noise. It's simply a path into the amplifier via the negative feedback loop. It would behoove you to read up on amplifier construction.

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Originally Posted by Theonetruegreg View Post

Have you happened to open any hi-end speaker's cabinet and peak around inside? Did you see twisted pairs in there? You didn't. It must be that wood is an amazing shield!

It's enirely possible his chosen length of speaker wire is some resonant fraction of the wavelength he is picking up. Say he's picking up RF @ 90 MHz (wavelength = 3.3m), a 1.65m speaker wire would equal 1/2 wavelength, a nice length for a 90MHz resonant antenna. Do your speakers have 5 1/2' lengths of extended wire in them?

Regardless, this bickering with you is pointless, so I'll not respond here further.
To the OP, hope you resolve your problem, be it with either the input or output wiring.
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post #33 of 50 Old 03-10-2012, 07:51 AM
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From what you said about the change when you moved things, there is not much question that the interconnects are the proximate cause.

Get the RF filters (ferrites) and clamp them to either end of each interconnect cable (Post#16).






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Originally Posted by AudioVideoPhilia View Post

Good to hear. I was not looking forward to tin foil wallpaper!

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post #34 of 50 Old 03-11-2012, 07:22 AM
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I was just thinking about posting the same link. Jim Brown offers quite a bit of expertise on the subject of interference, with this and other publications. He may get a bit "technical" for some people's tastes, but I've never seen him include any smoke, mirrors, or snake oil (cryogenic or not) in his work.

As for the speaker leads, leave them connected, but turn the amp's power off, and see if you hear a "peep" out of the speakers. If not, try connecting one cable at a time, and see where you start to hear the interference. You may have a loop of some kind that is resonant to the station's frequency, or maybe (not unheard of) a bad solder joint in a connector.

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post #35 of 50 Old 03-11-2012, 07:37 AM
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Here's a couple of interesting links from the same site:

http://audiosystemsgroup.com/bio-jb.htm

http://audiosystemsgroup.com/publish.htm

Although it's pretty deep stuff, here are some links that show how interference happens, and how people design their systems to deal with it. It's not light reading, by any means, but skimming through it can give insight in to how much of a "science" it really is:

http://www.arrl.org/files/file/Techn...I_Handbook.pdf

http://www.arrl.org/files/file/Techn...seHandbook.pdf

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post #36 of 50 Old 03-11-2012, 07:38 AM
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Quote:
Originally Posted by rntlee View Post

Are you purposely trying to come across as a dolt? The paper is about ferrite cores being used as low-pass filter to remove radio frequency interference...nothing magical there bud.



Once again, the "wire" is not the source of the noise. It's simply a path into the amplifier via the negative feedback loop. It would behoove you to read up on amplifier construction.



It's enirely possible his chosen length of speaker wire is some resonant fraction of the wavelength he is picking up. Say he's picking up RF @ 90 MHz (wavelength = 3.3m), a 1.65m speaker wire would equal 1/2 wavelength, a nice length for a 90MHz resonant antenna. Do your speakers have 5 1/2' lengths of extended wire in them?

Regardless, this bickering with you is pointless, so I'll not respond here further.
To the OP, hope you resolve your problem, be it with either the input or output wiring.

You forgot that he gets interference from FM broadcast. Unlike AM station, FM cannot be received and decoded by simple circuits. So it is very unlikely that it comes though common EMI path. Usually this type of interference comes from cross feed from another input, and happens in preamp. I am surprised that OP still gets it when his power amplifier s disconnected from preamp. There is definitely something in his surrounding, that receives FM broadcast and converts it into audio frequencies picked up but amplifier.
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post #37 of 50 Old 03-11-2012, 08:49 AM
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Rectification could be occurring in a bad solder joint, or any other non-linear device (like a transistor or IC that's getting hit hard by the signal.

Ken English, Sr. Engineer, KSL-TV.
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post #38 of 50 Old 03-11-2012, 09:47 AM
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Originally Posted by kenglish View Post

Rectification could be occurring in a bad solder joint, or any other non-linear device (like a transistor or IC that's getting hit hard by the signal.

For AM signal - yes, but not for FM. For FM signal to be heard, you need both nonlinear and resonant circuits to work together. This is much less likely occurs unintentionally.
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post #39 of 50 Old 03-11-2012, 03:30 PM
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Quote:
Originally Posted by ap1 View Post

You forgot that he gets interference from FM broadcast. Unlike AM station, FM cannot be received and decoded by simple circuits.

Hi Ap1,

I said that exact same thing once, but it turned out I wasn't entirely correct. Sometimes the theory has to give way to the realities of imperfect circuits.

The problem in my case was that the FM station had an AM component in its signal - a hard thing to avoid when high-power is involved.

Amplifiers are not always linear, and a 100,000 watt transmitter might not put out constant amplitude as the frequency is modulated. An FM receiver would not care, so there is no pressing need to fix it. So a high-powered FM station could have an AM component in its broadcast.

Then, all you would need is a diode to detect it.
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post #40 of 50 Old 03-13-2012, 11:24 AM - Thread Starter
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Over the week-end, the dealer who sold me the amp lent me a line conditioner and a high end AC power cord to test. It didn't help the RFI the amp is experiencing but the line conditioner does wonders for my plasma TV. But thats for an other forum. The RFI is strongest when the pre-amp is conected to the amp but still audible when the amp is powered on with only speakers hooked up. By wraping my speaker wires in tin foil I managed to reduce the RFI to the point where I only hear it when I put my hear right next to the speakers, headphone style. Unfortunately, when I hook up the pre-amp the RFI comes back as loud as ever. So I'll keep on tinkering with it for a while until I get fed up and ask the dealer to take it back.

Thanks for all the information guys!
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post #41 of 50 Old 03-13-2012, 12:09 PM
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Quote:
Originally Posted by AudioVideoPhilia View Post

. . . I was not looking forward to tin foil wallpaper!

Hi AudioVideoPhilia,

Sorry to say, but that may be you only solution, short of returning the amp. (Be sure the wallpaper is connected to ground).

The fact that shielding the speaker cables reduced the interference indicates that it is indeed entering through the speaker cables. The fact that plugging in the pre-amp makes it louder indicates that it is also entering through the line-level inputs. It appears that wherever the RFI can get in, it is getting in. So it seems to me that the designer of the amp overlooked the possible effects of a local radio station.

Bottom-line: It is simply a poorly designed amp.
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post #42 of 50 Old 03-13-2012, 01:02 PM
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Yeah, I'd try a different amp if you can. Different as in different brand, not just different model of the same.

Just because there is a knob doesn't mean you should turn it.
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post #43 of 50 Old 03-13-2012, 01:15 PM
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Just did a Google search on your amplifier, and saw a couple of posts about interference...especially from "HomePlug" (data via power line) stuff, getting in through the power input.

Did you try the ferrites? I would try them, right at (just as close as possible) the point where the power cord goes in to the unit. Try them on the power, and also on the speaker leads, again at the unit itself, simultaneously.
You want to block any path that can let the interference sneak in.

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post #44 of 50 Old 03-13-2012, 03:25 PM
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Quote:
Originally Posted by kenglish View Post

Just did a Google search on your amplifier, and saw a couple of posts about interference...especially from "HomePlug" (data via power line) stuff, getting in through the power input.

Did you try the ferrites? I would try them, right at (just as close as possible) the point where the power cord goes in to the unit. Try them on the power, and also on the speaker leads, again at the unit itself, simultaneously.
You want to block any path that can let the interference sneak in.

These ferrites are mostly to prevent HF leak FROM device, not into it. If level of RF signal in the room is within allowed limits, I would change the brand. Get something from major manufacturer. High volume manufacturers usually do more rigorous testing for EMI.
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post #45 of 50 Old 03-16-2012, 07:10 PM
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I would dump the amp off ASAP. There is probably no magic cure! A great deal of technical data has been presented here. You cannot overcome (easily) a poorly designed amplifier! One member mentioned the "high feedback" that "all" solid state amps use to acheive low THD...That is bunk!!! Some mfgs use a lot, some little and some none.

I live in a city with many radio stations very nearby and have never, ever had this issue, end of story. I have had ground loops (hums) caused by preamp amp combos but have never one time picked up a radio station! If you have not experienced this issue before it is not voodoo that will fix it. If you have to use a ferrite magnet to "fix" the Exposure amp, then something is wrong!

BTW, I use only SS amplifiers.
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post #46 of 50 Old 04-06-2012, 11:25 AM - Thread Starter
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Quick update. I brought the amp back to the shop so they could run some tests. They were able to reproduce the problem and they've greatly reduced the RF interference after a bit of soldering. They're waiting for an order of ferites to come in to see if they can eliminate it completely. They tell me they plan to use the ferites internaly. I'll know more in a few weeks.
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post #47 of 50 Old 04-06-2012, 02:34 PM
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Good to hear that they are doing what they can to eliminate your problem. I've had issues with radio stations nearby. I've either capped of the unused RCA inputs or soldered a 50 ohm resistor on a RCA connector and placed it on the inputs. It seemed to work.
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post #48 of 50 Old 02-01-2013, 08:34 PM - Thread Starter
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Just to close the book on this. It was all speaker cables' fault. Took a long time to get around to buying new ones because the RFI was down to almost inaudible levels but new Chord Company shielded cables fixed it once and for all.
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post #49 of 50 Old 02-02-2013, 11:12 AM
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Glad you got it sorted, bro.
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post #50 of 50 Old 02-02-2013, 12:24 PM
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Good grief, why put up with an amp that has obvious design issues when there are so many available that work the way they are supposed to ?

Regards,
Charlie

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