Monitor RF interference

pharao · Post by **pharao** » Wed Oct 13, 2004 6:23 am

I started building my home studio and unfortunately I'm receiving RF interference from one FM station (106.3MHz), so my two Roland DS-50A monitors are playng music anyway...

How can I avoid that?

Here are my specs

P4 2.4GHz based rig
M-Audio 1010-LT PCI card
two Roland DS-50A monitors, using 75 Ohms coaxial cable linked to SPDIF card output.

Thx

Post by **Aaronw** » Wed Oct 13, 2004 6:32 am

What other gear do you have inline? Is it coming through a particular piece of gear? Or does it happen while just playing back too?

pharao · Post by **pharao** » Wed Oct 13, 2004 8:26 am

I just turn the monitors on, the volume of each is totally down and I can hear the FM station , not too high but it is there. Even when playing back some piece the interference stills there, it sounds like a continuous background music and it seems to be independent of the monitor volume levels.

I have only the monitors and a Yamaha keyboard linked to the MIDI In/Out of the 1010LT.

knightfly · Post by **knightfly** » Wed Oct 13, 2004 9:41 am

If you have an extra computer surge protector, try plugging the power for your monitors into the surge protector which then plugs into the wall outlet; if the interference is riding on your power line, that should change it. It might not go away entirely, this is just an experiment to help tell where it's coming from.

Next, if you have some metal screening (like that used in door or window screens) you could try wrapping the speakers in that and clipping a jumper wire from the screen to your earth ground (be sure your screening is METAL, some of it is made of plastic but looks like metal)

If the screen trick works, you could maybe sandwich some of the screen between nicer looking wood panels and build boxes that are open on the fronts only, so you can still use the speakers with the shields in place.

Since the inputs to these monitors are digital, either the noise has to be getting directly into the amplifier circuitry or is being picked up by an external device BEFORE it is converted to digital and fed to the wires connecting the monitors; if you have nothing connected to them, then the interference must be getting into the analog amplifiers inside the speakers.

I checked Roland's site for help on this, and there is NOTHING listed for these monitors other than specifications - Not even a manual or schematic. If you have access to a qualified electronic technician, one possibility that may work is to have them install ferrite beads over the input connections to the analog amplifiers; but without a schematic, this could be time-consuming, expensive and possibly damaging.

That's about all I can think of for now, I hope it helps... Steve

pharao · Post by **pharao** » Wed Oct 13, 2004 9:58 am

thank you, Steve!

I'll try what you're suggesting and let you know soon.

Fabio Rahal

pharao · Post by **pharao** » Wed Oct 13, 2004 11:38 am

Ok, first attempts: I have connected the monitor plug to an UPS (unplugged from the wall outlet) and the interference remains

I'll try the screening.

AVare · Post by **AVare** » Wed Oct 13, 2004 3:47 pm

It is jumping into RF theory. What is demodulating the signal? FM can not be detected by a tubed diode or inuctance coupling.

Curious Andre

knightfly · Post by **knightfly** » Wed Oct 13, 2004 8:23 pm

Hey Curious, thought you'd never ask

Read the part here about slope detection -

http://www.tpub.com/neets/book12/51c.htm

http://www.somerset.net/arm/fm_only_lowtech.html

I've seen this happen in different ways - had a couple of cheap electret condenser mics that for some reason could detect FM, finally just quit using them since there's a strong station near me that I got tired of listening to thru those mics - also, I've seen cold solder joints act as diodes and under the right circuit conditions they can slope detect FM -

For all I know, there may be other ways as well; but this one could happen in the analog circuitry after gain controls, and you wouldn't be able to affect the volume with the level control... Steve

AVare · Post by **AVare** » Fri Oct 15, 2004 4:11 am

Thanks Steve!

Satisfied Andre

knightfly · Post by **knightfly** » Fri Oct 15, 2004 5:28 am

Man, that was almost TOO easy, makes me nervous

capps · Post by **capps** » Tue Dec 20, 2005 10:11 am

pharao wrote:I started building my home studio and unfortunately I'm receiving RF interference from one FM station (106.3MHz), so my two Roland DS-50A monitors are playng music anyway...

How can I avoid that?

Here are my specs

P4 2.4GHz based rig
M-Audio 1010-LT PCI card
two Roland DS-50A monitors, using 75 Ohms coaxial cable linked to SPDIF card output.

Thx

dude, i'm having the EXACT same problem with my event TR8s... i tried every outlet in my house and every single one of them are like a freakin antenna for some rap station!!!

capps · Post by **capps** » Wed Dec 21, 2005 6:25 am

after some serious research online i found that RFI are some nasty things! i bought a second power conditioner with RFI attenuation, and chained it with my other power conditioner that has an RFI filter. i was not impressed with the results. i was still getting frequency distortion and some FM radio station playing some stupid music that i didn't want comming out of my monitors!

so i called event.

they were more than helpfull, and made plans to accomodate.

after everything is resolved, i will let you know what the outcome is on the situation.

knightfly · Post by **knightfly** » Wed Dec 21, 2005 8:36 am

Cool, we'll be waiting; if there's any sort of "epiphany", I'll "sticky" this so others won't have to look so hard... Steve

kent clemmons · Post by **kent clemmons** » Fri Dec 30, 2005 4:12 am

A little info that may be helpful...
Interference like you described can be brought into a system two different ways:
1. conducted - The offending signal is brought in through the power or signal lines. A RFI filter, isolation transformer, or ferrites usually help.
2. Radiated - the offending signal is radiated onto the system through the air. Shielded cabling and a shielded box can help here.

In your case it looks like you are dealing with radiated electic fields. To screen them effectively requires a 360 degree shield around the speaker (like the screen that was suggested). The technique is called a faraday cage. the problem as I see it is that because it is radiated on to the whole system (electronics as well as cabling), you need to attack this from both directions. Just adding a RFI filter will leave the internal electronics open to interference and screening the box will leave you open to signals induced onto the cabling coming into the box.

knightfly · Post by **knightfly** » Sat Dec 31, 2005 9:28 pm

I agree; I'd save the Faraday cage til I'd tried ferrites, etc, though, considering the cost -

http://www.twpinc.com/twp/jsp/product.jsp?type=11

Steve

Oh, Kent - welcome to the board; could you please edit your profile to include a location (general) so we have an idea where you're talking from? Thanks... Steve

John Sayers' Recording Studio Design Forum Archive

Monitor RF interference

Monitor RF interference

Re: Monitor RF interference