RF Interference on my Event TR-8's - diyAudio
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Old 10th March 2004, 02:38 PM   #1
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Default RF Interference on my Event TR-8's

I just bought a pair of Event TR-8 powered studio monitors from a local retailer, and I'm hearing some noise like the sound of a muted TV plus a tiny bit of sound like that of someone talking or music from a radio/tv station.

With my balanced TRS audio cables plugged in, it sounds pretty bad and impossible to ignore. If I unplug the cables, the "person talking/music" noise is reduced, but i still hear it and the muted tv sound is still loud... Even when I unplug the TRS cables, I get it. so it seems to be coming in at least partially through the AC power cable.

Living in a high rise apt building, i tried it without the audio cable and just the ac power cord plugged in in different parts of my building. it got better in the kitchen, and better out in the hallway outside my apt. and virtually silent downstairs in the lobby. (i live on the 23rd floor)

my question is, are there any effective DIY ways to fix this? Event offered to fix it (i think by installing more capacitors or something), but if i could fix it without having to send it in the mail and not have it for several weeks, i would consider doing that. ferrite clamps? ac line filter? i think event tech support was somewhat skeptical as to whether these would work...

all help is greatly appreciated.
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Old 10th March 2004, 04:29 PM   #2
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Are you saying that this only started with the new speakers and that the problem didn't exist with your old speakers? It seems unlikely that a new set of speakers would cause this. Something is acting like an antenna and your amplifier is sending this to the speakers. Your description makes it sound like you suspect your AC source. This is not unreasonable. Amplifier power supplies are also subject to picking up RF interference. It would be helpful to try and narrow down when the problem actually started. Did anything else change besides the speakers?
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Old 10th March 2004, 04:38 PM   #3
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no nothing else changed. i don't have an amplifier for these speakers as they are self powered.

i didn't notice them with my old all-purpose panasonic home stereo. nor did i notice this with my sony mdr7506's plugged into my m-audio delta 44 soundcard.

the best conclusion i can come to is that there is noisy electrical wiring in my apartment, and that the event tr8's are not shielded that well.
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Old 10th March 2004, 04:45 PM   #4
HDTVman is offline HDTVman  United States
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Gandalf it may well be that you have some RFI. You said that these are powered speakers, correct? In high rise buildings one of the ways the owners increase there income is to lease space on the roof for Radio and TV transmission equipment and towers. Many times you may not know that this equipment is there untill somrthing like this happens.

The first thing I would suggest is to try some of those AC line chokes that Radio Shack sells. They are ferite cores that can be split and the AC cord looped through. If the problem is AC line related these should make a difference, maybe not fix but reduce. If there is no effect then the problem is internal and picked up by the low level stages, internal wiring or even the speaker and rectified by the output transistors. Then bypass caps would be the best bet. Unless you are experenced with this kind of problem it can be like chasing you tail.

Good luck

Later BZ
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Old 10th March 2004, 05:09 PM   #5
MBK is offline MBK  Singapore
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Default earth ok?

I would first check whether your earth ground (3rd prong on AC line plug) is actually connected to ground. If the internal amps have shielding, as they should, this shielding should be earthed.

Next test, check if it's still there if you short the inputs (shunt solder an input XLR plug without a cable attached to it: shunt hot=2 and cold=3 pins to ground=1 ). If it goes away, then it's picking up RFI at the inputs. In this case these additional caps they offered to retrofit may actually help without degrading the sound. They will put them between the signal leads and ground. Choke may help as well. Consider a common mode choke in that case, since you have balanced lines. This choke will only affect noise/RFI *common* to both signal lines.

MBK
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Old 11th March 2004, 12:29 AM   #6
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okay i'm assuming xlr are those big cylindrical plugs with the 3 prongs in the lower half of it. you're saying take one of those without the cable connected to it (which i don't have)?

exactly how do i shunt solder something. would that be like taking a flat head screwdriver and touching on two (or three) metal prongs at the same time?

sorry, i am a novice at this.
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Old 11th March 2004, 06:16 AM   #7
MBK is offline MBK  Singapore
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OK. Easiest way: Unplug the big 3 pronged thing, i.e. the XLR balanced connector. On your speakers you now see the balanced input socket. There are 3 holes, labeled "1", "2" and "3". The "1" pin is ground. So what you can try is to take a short, thin piece of wire and connect "1" hole to "2" hole. Then take another short thin wire and connect "1" hole to "3" hole. This basically makes a short circuit between the two inputs and ground. Both inputs now have "ground" signal, which means, zero. Remember, I am talking about shorting the *inputs* at speaker side, NOT the preamp output (preamp disconnected of course) . Do not short the preamp output, it may not like it.

If your noise disappears, that means that the cable (if connected) picked up RFI, and that the open, unprotected inputs (if no cable connected) also picked up RFI. If that's the case, either your cables and plugs are not shielded enough, or your preamp isn't shielded enough. It may in fact be your preamp - incidentally if you just plug in the signal cable at the speaker end but not at the preamp end, the cable *will* pick up noise - so you still don't know whether it comes from the preamp or not.

If however the noise doesn't disappear when you short the inputs, that means that the problem comes from insufficient internal shielding, or from a disconnected earth line, or from the AC power line (of the active speakers).

Alternative test, unplug the XLR connector, and fit some alu foil over the hole to see if it changes anything. In that case what you're doing is you shield the inputs from RFI (though alu foil is not a very good shield).

In any case - if they offer to install RFI filter caps for free, I'd go for it.
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Old 14th June 2004, 02:01 PM   #8
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I got my speakers back from Event. Well actually they said they lost my speakers so they replaced with a pair of speakers which were manufactured after a point at which they started installing better RF shielding in there speakers. or so they say..

anyways, the good news is that i don't hear anymore talking or music, but the bad news is i still get a noticeable hiss and buzz. the tweeter hisses, and the woofer buzzes... kinda like the noise a muted tv would make. is this sort of thing unavoidable?
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Old 15th June 2004, 03:29 PM   #9
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bump
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