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RFI noise/ FM overlay Any way to eliminate it?

I live in a high rise apartment in Honolulu Hawaii. Last year, I purchased a Jolida JD-9 phono pre-amp which mostly uses tubes. Right out of the box, it picked up RFI noise on one channel then overlayed the FM transmissions on both channels I tried everthing to eliminate it, but nothing worked, I subsequently sold the unit. I have avoided any type of tube components or hybrids. However, I have a chance to buy a used/VGC Musical Fidelity A-5 which uses a tubed output stage. My question is this will I experience the same RFI and FM interference as with the Jolida phono box because they both use one or more tubes.

I don't understand how design similarities(tubes)could possibly produce the same problems. BTW, There is a FM transmission tower about 1 mile away, but I don't know if its signals affect my building. Therefore, I need some advice as to whether I will have similar problems with CD player, and want to avoid hassles with the buyer regarding a return. I do use a power line condition, an Audio Prism Wedge which is about 15 years old; but it did had no affect on eliminating the problem with the Jolida. All advice and comments welcomed. Thanks, Jim
sunnyjim
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dhl93449
455 posts
 
You live only a mile away from a transmitting tower AND in a high rise apartment. Can you see the tower from your apartment? If so, you have direct line of sight beaming of high powered RF into your apartment.

If its a high power radio station, no wonder. I think your location/conditions are especially suited to exposure of the FM RF interference. If its entering you system via the air no line conditioner will help. You need better shielding on all your ICs and perhaps some 100 pF caps (polypropylene film or mica) on the input of your phono stage may also help, although this will affect your cratridge loading issues. I use ICs with a "balune" (sp?) or magnetic disc/bead at one end and these are pretty effective for RF rejection. Look into double or triple shielded ICs (such as two coax braided shields + foil shield). You cannot just warp aluminium foil around the outside of the cable, as you also need to ground the shield effectively. This is best done by construction within the cable.

Also, products that are contained completely within a metal box (like a CD player) are more immune to RF pickup via air than open chassis tube stuff.
sunnyjim OP
927 posts
 
Thanks to those who responded so far. Mezmo, I wrapped the PC cord o the Jolida phono box in aluminum foil as instructed by a friend and also the pre-amp PC. Nothing was improved!! I should have saved the foil for Thanksgiving left overs.

Al, I was thinking along the same lines as you suggested. that the single or multiple tube output stage of the A-5 CD player should produce much less signal to cause RFI problems

Lears; I do use a power line conditioner made by Audio Prism that is about 15 years old, and always was able to eliminate most RFI. When I lived in San Diego, I was about 2 miles from the Naval Air Station, and never got any errant transmissions from their tower
learsfool
1,215 posts
 
Another suggestion would be to make sure you have everything plugged into a surge protector. Most good ones include a filter for RF noise. Monster makes a very affordable product, for instance.
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almarg
9,670 posts
 
I think you are referring to the A5 CD Player, as opposed to several other types of components that Musical Fidelity also designates as A5.

If so, you are far less likely to have RFI problems from radio stations with a CD source than with a phono source, because the signal levels that are produced by a phono cartridge are vastly lower than those that are involved in CD playback. I don't think that tubes vs. solid state has anything to do with it.

Good luck!
-- Al
mezmo
516 posts
 
I guess I'll start with admitting that I am not really sure where you're RFI is entering the system. That said, I understand that the culprit is frequently the wires connecting the various components. Often, better shielding on the interconnects can help. Also, know that Radio Shack (and likely others) make a magnetic "RFI Blocker" that clips over the interconnect itself, with the stated goal of disrupting any RFI picked up by the wire (which, in effect, acts like an antenna). Can't say whether these work.

Did you experiment IC's and shielding? If not, may be worth a try. Otherwise -- and if it's the tubes themselves that are picking up the RFI (which I don't know whether this is either possible or the case for you) -- I'm out of ideas other than trial and error. (And the hope that someone else knows better than I, which is not exactly a tall order...).
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