R.F.I. issues

[bsco]

Got a couple of Yorkville YSM6 studio monitors and the owner has issues with both of them picking up radio signals from one of the local stations......I asked him about cables, etc and he said he has tried different cables with basically no change....he has moved and the units are still picking up those freq but not as loud as before in his previous location....I have a feeling that I am not going to find any issues with these but I am going to open them up and have a look around...just thought I would post this just in case somebody here has had similar issues with radio freg interference with audio equip.....
Cheers

[Jazz P Bass]

AM or FM?

How long is his cable run?

Chances are that you will not be able to duplicate the issue on the bench.

[nosaj]

AM or FM?

How long is his cable run?

Chances are that you will not be able to duplicate the issue on the bench.

If you unplug the cables from the monitors, does the noise stop or continue? If it stops, the noise is being picked up in the cable or in the connected device(s). If you are using 1/4" SPEAKER cable. If you are using powered speakers, you should not be using speaker cables. You should be using 1/4" TRS balanced cables, which are much, much more immune to outside interference and noise. Balanced TRS cables are just as good as XLR cables for hum and noise rejection. And you don't need Monster cables our expensive cables.
You would need to identify your interface and monitors for me to confirm that they have balanced inputs and outputs. Most do, but some very inexpensive models do not.
nosaj

[Enzo]

Chances are he was using all various cables from the same source. Please try a different source. Get a CD player or cassette deck and plug directly into the speaker. These are powered speakers. If the RF remains then indeed the speaker or cord has issues. If the RF is gone, then it was coming from the source feed.

And agree with Nosaj, can't use "speaker cords" here.

[bsco]

Thanks for the replies guys...I don't quite know what he is using..he dropped these off to the store...they checked them out and couldn't find anything wrong......but he insisted so they gave them to me.....I know for a fact that I am not going to be able to get this to happen here in my house......he said he has tried other cables, power bars, etc, etc.....and even one of his friends bought their monitors over and no issues....I have no idea of what he is using but it sounds like he is using computer and interface.....I will have to call him again and I might have to go to his location in order to check it out.......I can't see how he would be using speaker wire as they are powered monitors.....I will go ahead and test them here and if ok I am going to bring them back to the store and take it from there.....I'll let you know what happens here.....
Cheers
P.S. I forgot to mention.....apparently, when this radio station is picked up, it is accompanied by a "Low-Level Hum" ......at least that is what the ticket says.....

[bsco]

Ok. It is 7 AM now and I had both of these on for a couple of hours...I ran a 50 ft speaker cable to the input and turned up the volume just enough to hear it....I got the usual noise that would be associated with a non-shielded cable but I never picked up any radio stations....I will have to bring this back and let the customer take it home so he can try it...if he still has issues, I will have to go to his location to see what is going on depending of course on where he is........I can not re-create the problems here......I'll see what happens.....
Cheers
P.S. cd player that I have works fine and my rca cables are good....

[Enzo]

My shop used to be half a mile from an AM radio transmitter. I could pick up their modulation envelope all over my shop, Even just watch it on my scope. So he may be much closer to such a source than you.

ASk HIM to plug a CD player directly into it at his location, and does it still get radio? That will tell us if it is coming in with the source or not.

[bsco]

My shop used to be half a mile from an AM radio transmitter. I could pick up their modulation envelope all over my shop, Even just watch it on my scope. So he may be much closer to such a source than you.

ASk HIM to plug a CD player directly into it at his location, and does it still get radio? That will tell us if it is coming in with the source or not.

I will do that...he is much closer to a "Repeater" transmitter...actually, pretty much directly across from it if you go by "Line of Sight" I will get him to take these back and try them again with a cd player....

[eschertron]

I will do that...he is much closer to a "Repeater" transmitter...actually, pretty much directly across from it if you go by "Line of Sight" I will get him to take these back and try them again with a cd player....

Sounds like the problem he wants you to solve is a site shielding issue, not a component issue.

[bsco]

Sounds like the problem he wants you to solve is a site shielding issue, not a component issue.

Yes. That is what it sounds like.....We'll see what happens....
Cheers

[nevetslab]

Yes. That is what it sounds like.....We'll see what happens....
Cheers

And, there's a good chance he's on the same ground plane with the 'Repeater' transmitter. So, it's (the RFI source) on any grounded equipment that gets to AC mains ground.

[nosaj]

Sounds like the problem he wants you to solve is a site shielding issue, not a component issue.

You're not selling it right . It's a feature not an issue. I mean who else out there has monitor that can pick up the radio station. Embrace it noise rock style.

nosaj

[patlaw]

The speakers are not going to pick up RFI unless you're in a high enough RF field, like Enzo was in. The speakers were probably not designed to work in high RFI environments. I used to be an engineer at an AM radio station and had to deal with RFI all the time. The worst situation we ever solved was at a friend's 50KW AM radio station. He had a custom audio console made with discrete transistors. The problem was solved by adding caps between the bases and collectors in various stages of the buffer and output amplifiers. The caps actually reduced the bandwidth of the circuit. The change did not affect the quality of the audio since the roll-off was above 20 kHz. The station was at 940 kHz. We often had to do the same in op-amp based circuits by adding capacitance around the feedback resistor in inverting circuits.

[bsco]

The speakers are not going to pick up RFI unless you're in a high enough RF field, like Enzo was in. The speakers were probably not designed to work in high RFI environments. I used to be an engineer at an AM radio station and had to deal with RFI all the time. The worst situation we ever solved was at a friend's 50KW AM radio station. He had a custom audio console made with discrete transistors. The problem was solved by adding caps between the bases and collectors in various stages of the buffer and output amplifiers. The caps actually reduced the bandwidth of the circuit. The change did not affect the quality of the audio since the roll-off was above 20 kHz. The station was at 940 kHz. We often had to do the same in op-amp based circuits by adding capacitance around the feedback resistor in inverting circuits.

I think these monitors are not internally shielded very well....his friend has a set of KRK"s and these will pick it up but it is so low in level that you have to strain your ear to hear it( that is what the owner told me)...anyway, if he wants me to drop down to his location to check it out it will be up to him....he was located in another area before he moved and there were no issues....by the way, what value of caps did you use???
Cheers

[patlaw]

....by the way, what value of caps did you use???
Cheers

I don't recall, but it wouldn't matter anyway. The value of the C in an an RC filter depends on the value of R. So, while I may have used 10pF, you may have to use 100pF or 1000pF. The frequency of the RFI also matters. AM RFI usually requires a cap. FM and higher frequency RFI can often be handled with ferrite beads. Magnetic interference is a bear. I currently have a microphone/mixer setup in a doctor's office that is picking up electromagnetic interference like crazy. It's actually being picked up by the microphones. I had to get mics with built-in humbucking coils to have a workable solution, but even then, I had to use a pair of dbx 286s mic processors with gates to mute the noise.