[Rob N]

I’ve been using an Earmax Pro with Grado RS 1 headphones for about 3 years and up until about a year ago everything was fine,but one night I was listening to a CD when I heard a foreign (German I think) radio station faded in briefly and then disappear .The same thing happened roughly 1 or 2 times every 5-6 weeks (which I could live with) but recently it’s got worse, every evening last week it happened between about 7pm and 9pm,last Sunday the station faded in and out constantly for about one hour. I’ve tried disconnecting the interconnects and listening ,trying different tubes, turning off all other equipment and moving the amp to a different position all failed to make any difference. I’ve tried using a different amp and the problem goes

Has anyone else had a similar experience?

 

[Mighty Mik]

Welcome to the world of short wave listening.

 

[Kubernetes]

Well, if my cell phone (1900Mhz GSM) is within a few feet of the EMP, any incoming calls create a buzzing sound through my Grados. This goes away if I place the cell phone farther away. Question: is there anything close to your EMP that might be acting as an antenna?

 

[JML]

You could try getting woven RF shields for the tubes and ferrite cores on the cabling. #2 is far cheaper, and while I've heard of #1, I don't use tubes and I have no idea where to get them. But the first thing to do is make sure you have an effective ground connection. Any cable between the AC line and the headphones can be the culprit.

At night, atmospheric conditions can bounce radio signals over a wider area than during the day, which accounts for the time differences you experience. Good luck trying to solve the RF problem -- it can be a real pain to diagnose, and worse to cure.

 

[Mighty Mik]

Anything connected to an input is antenna. I'll bet you're using unshielded wire somewhere. Grounding is important as well. One of your leads may be just the right length (1/4 wave) for an antenna. If you listen to it carefully, maybe you can get a callsign and frequency.

Quote:

Originally posted by Kubernetes Well, if my cell phone (1900Mhz GSM) is within a few feet of the EMP, any incoming calls create a buzzing sound through my Grados. This goes away if I place the cell phone farther away. Question: is there anything close to your EMP that might be acting as an antenna?

 

[Rob N]

I've tried running it without any interconnects and the problem is still there.The only thing I can think of is atmospheric conditions and I may have to wait another 3-4 days for those to change (last week the problem was there every night but the week before everything was OK)

 

[Mighty Mik]

Where in the world are you? I havn't noticed any extrordanary conditions (flux is declining

) , but if you happen to be in europe, it tends to be an RF rich enviroment there. Make notes...is it the same station, at the same time every day? Different stations? frequency?

 

[MirandaX]

The power cable is also a big possibility. I have one piece of audio equipment that picked up a local FM station until I replaced the power cable with one that had better shielding.

 

[Mighty Mik]

I'll second the power supply as a possible source...i'd try a choke as close to the unit as possible.

 

[Rob N]

Found 3 TDK ferrite clamps and put one each on the interconnects and one on the power lead, I also twisted the interconnects together. I have been listening for the last 5 evenings and almost all the RFI has gone.