I would try to shield as much of the phono leads as possible.In some cases this may be as easy as replacing an unshielded wire with a properly shielded one or as difficult as trying to wrap delicate leads from your cartridge with shielding. It could also be the cartridge itself that is picking up the RF - try switching carts to see if the problem persists or changes.
Can you isolate the frequencies of the FM signal? On an active guitar pick-up system (a Gibson ES- Artist) that had RF issues I could even hear the program material (it was an AM religious station).
You may be able to do electronic shielding if you can identify the frequencies that are bleeding through, but an electronic filter may have an audible effect that is more pernicious than the original problem. |
Quoting from a response I made a while back when someone else had a similar problem: I believe that oxidized or dirty contacts can cause that, particularly as here where low level signals are involved that are subsequently subject to high gain. The poor contact results in diode rectification effects, which demodulate the radio signal.
Try using some contact cleaner on all of the connections that are involved, including the ones in the headshell that mate to the cartridge pins, as well as any other connections that are in the path to the phono amp. Or, as a minimum, just slide each of those connections off, and then back on -- that might rub off the oxidation sufficiently.
Also, I assume that you hear this pickup with your FM tuner turned off. If that's not the case post back. Good luck, -- Al |
Almarg...A corrosion-formed diode can indeed rectify an AM station's signal so as to produce recognizable audio. In my experience what you usually get is a mixture of several stations, some louder than others.
However, it takes a lot more than a diode to pick up recognizable audio from a FM signal. |
A corrosion-formed diode can indeed rectify an AM station's signal so as to produce recognizable audio. In my experience what you usually get is a mixture of several stations, some louder than others.
However, it takes a lot more than a diode to pick up recognizable audio from a FM signal. Hmm, yes, you have a good point there. But still, if we understand the facts correctly (recognizable audio from fm, being introduced through the phono input, and present (I assume) when the fm tuner is turned off), SOMETHING in the phono path is somehow demodulating the signal. Not sure what that could be. Regards, -- Al |
Thanks for the suggestions -- will give them a try. Just completed a year long renovation. The equipment was originally in the center of the house and rarely if ever had an RF problem. Now, equipment is housed in a wood cabinet against an exterior wall. A new FM antenna is about 10' from the turntable on the eaves. Disconnected the cable to the antenna and still have RF signal. The same station comes in when the night signal changes. It makes no difference whether the tuner is on or off with the RF. Again, during the day, phono is dead-quiet. |
This is just a wild guess, but since it's only happening at night, could it somehow be related to the fact that lights are on (vs. during daytime)? I'm no electrician, but it seems that the difference between night and day might be the clue here. I wonder if the house wiring is somehow acting as an antenna/repeater (from the renovation you mention) is causing the issue, but only when the circuit is closed such as when lights are on.
Again, a wild-assed guess at best but logic dictates ruling it out as a cause. |
Are you using a tube or solid state phono stage?
I had similar problem and after trying many great tube phono stages, eliminated the trouble only by switching to ss phono stage. Cheers,
Spencer |
Are you really sure that it is an FM station you are hearing? There are two things that seem to point to AM -- the fact that it is being demodulated into understandable audio, as discussed above; and the fact that the problem occurs only at night.
My suspicion would be that the day/night difference would be caused by differing signal strengths before/after sunset. As you probably realize, AM stations typically propagate much further at night than during the day. With FM, I believe that would only be true to a slight extent if at all.
If the other suggestions don't help, you might try this: There are kits that are available (I used to have one) that provide small value capacitors on rca plugs, for the purpose of optimizing the capacitive loading that is applied to the cartridge. Or you can solder up something like that yourself. If you were to add say 50 or 100pf of capacitance (connected at the preamp input with a y-connector), without going outside the range of total capacitance that the cartridge is specified for, the extra capacitance might load down the rf pickup sufficiently to kill it.
Also, you could try to find the kind of ferrite-based rfi filter that has a donut-hole in the center, through which the phono cable would be routed. That might do the trick as well. I think some of them are specifically marketed for audio applications.
Regards,
-- Al |
Again, thanks for the suggestions. Makes no difference whether the lights in the house are on or off. For the renovation, the entire house was rewired. I have a dedicated circuit for the stereo. I tried plugging the equipment into different sockets on different circuits: made no difference to my problem. Did read that radio broadcasts are different at night, thus getting the signal when the signals are altered. It's the same FM station and begins around 5- 5.30 PM until after midnight. During the day, absolutely dead quiet. My phono stage is tube. Tried changing the tubes in case one or all were picking up the RF. |
Some FM stations also broadcast on AM (or used to). Since demodulating FM by accident is virtually impossible something like this should be investigated. Many AM stations are required to REDUCE power at night because the signal travels so much further...to places where another station operates on the same frequency.
Are there any practical jokers near you? |
I had a very similar problem also with a gyro se using a stock rb300 arm. In my case it was the tonearm cable picking up an am signal, I have no idea why but I was able to virtually eliminate it by reversing the phono inputs into the phono pre (plugging the left phono plug into the right input and right plug into left input) of course then I also had to reverse the leads from my phono pre to my linestage. Don't know if that's an option but it's easy to try. |
The RF I'm getting could very well be AM, I haven't listened to AM for years, so made this mistake, regardless, still getting RF at night, Spanish speaking talk radio -- any suggestions on brands of a ferrite RF filter? Will also try switching the tonearm cable. Again, thanks for all the suggestions. |
Here's an excellent paper, dealing with rfi problems caused by ham radio systems, but providing a lot of information that may be applicable to your situation as well: http://www.audiosystemsgroup.com/RFI-Ham.pdfHere's a link to the catalog of Fair-Rite, which makes a lot of these things: http://www.fair-rite.com/newfair/index.htmRadio Shack (you'll pardon the expression :)) sells some snap-together ferrite choke cores, part numbers 273-104 and 273-105 according to an older catalog I have. Hope that helps, -- Al |
Almarg, thanks for the article and link to suppressors, am pursuing -- |
mouser.com also sells cheap ferrites. |
I tried ferrite suppressors which didn't work: cable suppressors and ferrite beads.
Someone suggested lead sheets to line thecabinet the turntable sits in -- if Superman can't see through the stuff, then maybe radio wave as well -- anyone have any thoughts or knowledge???? |
How about the other suggestion I had made, adding a small amount of capacitance via a y-connector at the preamp inputs (the capacitors being soldered to rca plugs that would plug into the y-connectors)? As I indicated, the only caveat would be to make sure you are staying within the range of total load capacitance recommended by the cartridge manufacturer. If you have a moving coil cartridge, load capacitance is most likely very non-critical.
Regards,
-- Al |
Copper is a lot safer than lead, and would provide the same benefit. If you go this route research the term, "Faraday Cage", which is a lab quality box. The problem is that you need cables going in/out and that often corrupts the ability keep out the RFI.
Borrow a solid state phono stage before you conclude anything else or spend big bucks. Trust me, I struggled w/this crap for YEARS! Cheers,
Spencer |
Al & Spencer thanks for your input.
Al -- my cartridge is a Grado MM. Would you please exlaborate what sort of capacitors to use. I'm not too electronically literate.
Spencer -- I did hook up to a solid state phono stage. Did get RF, but was able to manipulate the turntable ground and this eliminated the RF.
Here's something more puzzling. When I re-plugged my turntable into the Rogue 99 tube phono stage, I noticed that the RF disappeared when I touched the pre amp. At first it was my arm on the pre amp with my fingers touching either the turntable ground wire or the turntable leads. I thought great, if only I can find a spare arm to leave on top of the pre amp. The heat would probably make it stink up my living room though. Then I realized if I simply touched the pre amp, the RF disappeared. I tried a separate ground to the pre amp, but this did not prove successful: the RF was back. Yet, when I laid a hand or fingers on the pre amp, the RF disappeared.
If you guys have any more suggestions, I'm game. I feel now, there has to be a simple solution, I just don't know what it is. |
Can you tell me exactly what model Grado it is, so I can look up its recommended range of load capacitance. Although many of the Grado's are fairly insensitive to load capacitance, which may be helpful. Also, how long is your phono cable (which adds significant capacitance)? I'll then try to pick out a suitable capacitor.
Your body has capacitance, and that is why touching the preamp affects the RF. When you say you connected it to a separate ground, if you just used a plain wire to do that, the wire's inductance may have made it ineffective at rf frequencies. What you should probably try is a braided ground strap instead, which makes for a much more effective connection at rf frequencies. Or as a temporary experimental arrangement, if possible, try making the ground connection with the shield of a coax cable.
I should have a little time tomorrow to research these parts further.
Regards,
-- Al |
Al -- my Grado cartridge is the Reference -- out put 4.0 -- length of the cables are approx. 24" -- they came with the Techno arm for the Michell Gyro Se -- again, I really appreciate your thoughts and suggestions regarding this --
Brian |
I have a 4mv Reference Sonata, which simply says "insensitive to load capacitance," and I suspect the Reference is similar in that respect. Also, your phono cable is very short. Both of these factors suggest that you can feel free to add any reasonable amount of capacitance, perhaps up to a few hundred picofarads (pf), without affecting the sound at all. But it may not be necessary to do that, if a good ground strap would have a similar effect to what you found when you touched the phono preamp. It looks like the best way of getting that, without having to purchase a large quantity from an industrial distributor, is via e-Bay. You can search there under "ground braid." Here is one good example: http://cgi.ebay.com/20-Tinned-Copper-Braid-3-4-Flat-Wire-85A-Max-Ground_W0QQitemZ370134600553QQihZ024QQcategoryZ26213QQssPageNameZWDVWQQrdZ1QQcmdZViewItemIf that doesn't do the trick, and you want to try adding capacitance, it looks like no one makes anymore the kind of kit I referred to, that I had many years ago, containing a set of capacitors installed on rca plugs. So you'd have to make your own. Here is one example of a y-cable that you would need; there are many others, as you no doubt realize: http://www.bhphotovideo.com/c/product/488449-REG/Phoenix_Gold_ARX_569_Silver_500_Series_RCA.htmlThe most convenient and inexpensive way of getting the rca plugs and capacitors would be, if you can stomach doing so, from Radio Shack. Their part number RSU 11537479 is a set of four gold-plated rca plugs. Part numbers 272-123 (100pf), 272-124 (220pf), and 272-125 (470pf) would be reasonable capacitor choices. Start with the 100pf, and if that doesn't do it go up from there. You can also find suitable capacitors, with similar values, here: http://www.tubesandmore.com/Or if you want to wade through a vast selection of potentially higher quality parts, from an industrial distributor, go to http://www.digikey.comYou would have to be prepared to solder the capacitors to the rca plugs, of course. But it might be simplest to start by trying the ground strap approach (using it either in place of or in parallel with the ground wires you've tried -- it shouldn't matter which), which could very conceivably solve the problem. Regards, -- Al |
Thanks Al, will get on to your suggestions and see what happens -- might take a few days -- again, thanks for the input -- |
Al & Spencer -- wanted to thank you guys for the helpful information to eliminate the RF coming through my turntable -- the final solution: braided ground wires from my preamp & amp to the power conditioner's ground. So far, good listening -- |
Glad to have helped, and thanks for letting us know. This seems to be a not uncommon problem, and your info will be helpful to others.
Regards,
-- Al |
Adding an additional ground wire from my pre-amp to power conditioner fixed my
radio interference.
|
