FM radio interference in Marshall 100w 2203 head

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4/1/2003 7:09 PM

Steve

FM radio interference in Marshall 100w 2203 head My friend's home studio is situated about 500 feet from a tower that broadcasts a local FM radio station. Although other equipment in the studio rarely picks up the reception, my Marshall amp seems to really like it. I've had my amp there for the past 3 years, & the radio reception seems to have gotten worse. Even when plugging straight into the amp, you can make the radio louder by moving the guitar & cord.     I'm not sure if the station has increased broadcast power recently, or if something in my amp is going South, making radio reception more audible.     Any clues before bringing my amp to the shop?     Like I said, the sound of the radio has always been there, & is more pronounced when using a string of boost boxes, but I just want to make sure it's not something with my amp. This only happens at his place, no where else.     Thanks in advance,   Steve

 

4/1/2003 9:12 PM
Armand	Does it happen with the guitar and cable unplugged from the amp? If not, I wouldn't suspect the amp. I would look at the pups and the cable. Somethings acting as an antenna especially since you said you can change the intensity by moving the guitar around.

 

4/1/2003 10:36 PM
Steve	I'll have to check. I seem to remember hearing it slightly even with nothing plugged in, but I could be wrong. BTW, I'm using a modified Strat with a Duncan JB in the bridge position. George L's cables.     Thanks,   Steve

 

4/1/2003 11:02 PM

MBSetzer

Very often this is due to corrosion on the input cables and/or jacks of the amp or certain pedals, poor connections in general are sometimes bad but may be enough to cause problems constantly so close to a transmitter.     All the cable ends and jacks should be cleaned with Deoxit, and if there is any visible tarnish or corrosion they should be polished up or replaced beforehand.     Also, if there are any solderless connections inside one of the cable plug ends, it might help to solder them so that connection can function as a conductive unit rather than a friction joint betwen two dissimilar metals. The plugs & jacks which need to be unpluggable are just friction joints but you don't want more of them than you absolutely need, and the contact tension should be tightened up if necessary.     Regardless, there are some combinations of plug & jack alloys which tend to pick up radio better than others, if you carefully check every cable & pedal independently, you may be able to pinpoint a single problem plug or jack, and replacement may be necessary if nothing else helps.     Mike

 

4/2/2003 4:53 AM

Richie{~}==:::

Not much to add, but a question..what are the pedals on.concrete floor will also cause problems or a rug over concrete..you'll hear a difference if you just pick them up a little bit. But also cord lengths can be like antenna.. try to use good cables.. And if its only happening at the place close to the Tower..it may be hard to get rid of it. Using shielded input cable to the tube may help some..   Richie

 

4/4/2003 6:28 PM
Steve	Thanks for all the suggestions to try. I usually go to the studio at least once a week, but my friend cancelled this week, so I'll have to wait until next week to try a few things.     Once again, I appreciate all the help!   Steve

 

4/3/2003 4:11 AM

Ken Brakebill

Try connecting a wire from the barrel (ground) of your guitar cord plug (at the amp) to the metal chassis. If this reduces or eliminates the RF noise, you will benefit from replacing the Marshall style input jacks with switchcraft jacks that ground at the front panel. You will have to convert to star grounding near the input jacks if this increases hum. I had to do this to a JTM-45 that was unuseable until I made this conversion.     Good luck   Ken

 

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