New Subwoofer Causes A Lot of FM Interference - Why?

[nola]

I just put the 2nd sub into the bedroom. 1st stop, right next to the existing RSW-15. Started to test it out. First tests were ok as far as bass response goes-although the curves were quite different from the RSW.

Had to use a cheater plug to get rid of hum. Currently, the sub cable from the receiver goes to a Y split, with 1 Y plug to the MFW and 1 cable after the Y split to the RSW. Signal strength to the RSW must still be pretty strong, despite the split as the RS SPL meter still reads about the same.

However, the new AV123 MFW-15 sub (I think with the new redesigned amp) causes enormous FM interference when it is turned on. The interference can sound like added static on stations with decent signals. Other stations sound normal. But with some stations it totally wipes out the FM signal and you get sort of loud chortling sounds - unlike anything I have ever heard before. My receiver is an Onkyo 805, and I use one of those cheap rabbit ear and loop tv antennas for the FM antenna. The RSW is about 5 ft from the antenna. The MFW is about 2 1/2 feet away from the antenna.

I had a few issues pulling in weak signals before, but never any interference like this.

Anybody have any ideas on what is going on or how to fix it? I plan to call AV123 too.

[CECAA850]

Have you read THIS thread?

[WMcD]

If I may respectfully disagree with my brother from Texas.

That link describes a problem caused by the cable TV. The shield has some a.c. on it. As a result it pulls up the chassis "ground" of whatever it is connected to. Then anything which has a signal referenced to ground "sees" the small a.c. signal.

Isolation transformers solve thisissue because it elimiates the direct connection between the transformer's input and output . . . and it does not pass a freq that low. A good system wide ground will wor too. I dislike the notion of lifting grounds with cheater plugs. In any event, the 60 Hz a.c. is not radiating.

As described in the problem before us, something in the sub amp is putting out radio frequency noise. Perhaps a switched power supply or class D amplifier. Naturally a proper design job pervents this from getting out of the subwoofer.

It is quite possible that the a.c. line cord is radiating the r.f. noise, as an antenna. Whatever wire is running the audio signal into the sub could be doing the same.

One possible solution is called a ferrite bead. It is not really a bead as we think of a piece of jewelry. Here the soft iron core absorbs the r.f. running on the cord. Place it close to the sub.

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=110-452

You'll note there are different sizes and they are inexpensive. You might consider buying several and experimenting. And while your at Parts Express there is always the temptation to buy some additional audio gear . . . but be strong! (I have stumbled.)

You may have seen similar things on computer equipment.

No guarantees this will work but it is a good bet. It will not prevent a signal radiating directly from the inside works.

Wm McD

[CECAA850]

If I may respectfully disagree with my brother from Texas.

Not a problem.

He DID say he's using a cheater plug. I thought that the referenced thread might help him get rid of his cheater (for safety reasons), but we won't bring up THAT debate.

Carl

[DrWho]

I wonder if they actually go through FCC testing and all the other global compliance requirements....

"Operation of this device is subject to the following two conditions: (1) this device may not cause interference, and (2) this device must accept any interference, including interference that may cause undesired peration of the device."

I suppose there could be loopholes for smaller businesses?

If you truly believe that it is RF interference, then you might try wrapping your subwoofer in aluminum foil. It would need to have no holes and it should be tied to the ground on the amplifier (usually any metal bits, like on the plate amp will be ground).

Switching supplies/amplifiers can be notorious for spraying RF all over the place.

[nola]

Thanx for the replies so far.

I also posted this at avs forums after a google search showed other sub owners also had similar issues likely related to the amp:

http://www.avsforum.com/avs-vb/showthread.php?p=16964345

AVS Forum > Audio Area > Subwoofers, Bass, and Transducers

Official Elemental Designs Subwoofer Thread p.253 exerpts- "Second issue: When I switched to the FM tuner I found that the sub is creating a MASSIVE amount of RF or electrical noise that completely interferes with FM reception. The only station that will come in at all is a powerful station whose transmitter is only about 5 miles away. All other frequencies have too much noise to tune, with a rising/falling sweep-type tone. I also found that the noise changes some when the level knob is adjusted, sometimes being just "noise" to changing to the rising and falling sweep-type tone, to noise again, depending on where the level is at. The noise also still occurs if the RCA plug is disconnected. Strange. I can't imagine this is normal." "I've never heard of an amp generating massive amounts of interference in the FM range. I'm sure Alex will let us know why this is fantastically unlikely from an electrical standpoint." "I haven't either. All I can say is that, turn the sub on, the FM reception goes bad, turn the sub off, everything goes back to normal." From me on Friday: "Well, you are not alone in FM interference problems with your sub amp Well, you are not alone in FM interference problems with your sub amp I posted this yesterday at: http://www.tweakcityaudio.com/forum/...ead.php?t=1794 and in the klipsch forums ............................ Most all replies that I got were related to ground loop hum. That was a problem that was easy to fix: cheater plug. That was NOT my issue. My issue, perhaps like yours was that although some FM stations were ok, some had lots of static. At some FM frequencies, I got lots of sort of chortling noises that were kind of loud. I called av123 today and talked to the owner, Mark L. Schifter. He told me to use ferrite EMI / RFI traps. I had some (ok about 10) from Parts express. I used them on the ac plugs both near the outlet and near the component for both sub and receiver and for the sub cable (with RCA connectors), and even on the FM antenna I use. Also tried all of this with and without cheater plugs and even using different wall outlet. Well, all of this, which may have worked fine for others, only worked for a few seconds for me. After turning the MFW amp back on, a few seconds later, the noises started again. Also, even with the RCA plug disconnected, I still got some buzzing noise. All of these issues only occurred at certain frequencies and were not uniform in the FM band. I unplugged the MFW and just use the RSW sub from Klipsch now. I will call av123 back on Monday. I am not happy. I am also concerned that the amp design did not shield the RF issues sufficiently. Perhaps that is your problem as well. If we share a common problem between manufacturers, perhaps the Consumer Product Safety Commission can tell us what acceptable levels of RF leak are, and if there is a way for to test for it. Any comments appreciated."

CECAA850 - nice link on hum, but with the cheater plug in use, not an issue now. I also bought some parts express isolation transformers about a year ago, pinky finger size. But due to construction in the main room, I cannot get to them quite yet.

Mr. McD: MS at AV123 also suggested the ferrite RF traps. I tried them (I have about 10 in the bedroom). Well, at best, only stopped the EMI for just a few seconds, then it came back. No apparent regard to use of the cheater plug. Pls see above. I have not moved the av123 MFW sub this weekend - had to spend the whole weekend on kitchen issues.

Thinking about it, I did not try them on the cable line itself. Hopefully I will also be able to get to the isol xfrmrs this week too.

Cheater plug: pls don't shoot me: as a non electrical engineer, my guess is that on well made new gear, the ground plug probably is only there to keep the us and european regulators happy. Using it to rid hum is for me a great $1.00 solution.

.Now, in his book, "Get Better Sound", Jim Smith also talks about possible polarity issues and cheater plugs. But such discussions are beyond my knowledge - and maybe my hearing - at this point.

.Dr. Who: I think we might like to know who, if anybody, actually regulates this stuff. As in, "is anybody there....does anybody care..." MLS at av123 did tell me that they had make a product that would pass US and EU (ce label) standards. He indicated, this alone required the use of the 3 prong cord. Pls note that the 1999ish RSW-15 does not use the ground prong.

.

But I am not going to wrap a sub, nor an amp in foil at this point. (Well, if I was Cristo, 30 yrs ago....) But putting mu metal around the proper parts of the amp might be an idea. However, exactly where to put it, etc, is beyond my knowledge. Mu metal is not cheap either. It is used in some MRI applications.

Like with the RSW sub, if you take out both pieces of the MFW amp and control plates, you have unwanted holes. In short it would be a mess. Hopefully the folks at av123 will have a new idea on Monday. I also have sub amps from the main room and an Adcom beast too. But why should I have to use another amp?

.

But let the buyer beware of FM interference as a potential ?new issue for sub amps that might be, shall we say, sub-par.

[colterphoto1]

I have, at various times, wrapped my head in aluminum foil. This has not stopped the voices.

[BigStewMan]

I have, at various times, wrapped my head in aluminum foil. This has not stopped the voices.

But we're you facing magnetic north?