Changing the loading of the cartridge made a colossal difference. At 500 ohms it essentially went away. Also, I cut up my sheet of mu metal and placed it around the phono preamp (bye bye aesthetics), and that helped too. So the problem is more or less "solved." Thank you all for your suggestions. It turns out that the radio station I was receiving so well recently went from 1 KW to 10 KW (it is less than a mile away), and that certainly did not help matters either. In fact that probably was the major culprit. |
The first place to look, if my experience is anything to go by, is cabling. Sometimes moving your phono cables, orienting them differently, will solve an RF problem. If you haven't done so already, make sure that if they cross AC wires, they do it at right angles.
If that doesn't help, your phono stage or amp may need better RF isolation, or you may have a tube that is particularly sensitive to RF. Also check your AC line for proper grounding. To isolate from RF, you can cage the amp with wire or a metal box, and ground the cage.
Let us know what you discover, if you get the chance. |
Hello everyone, I have a similiar problem but more problematic? as I have a radio station coming in on one of my Lowther Mau horns! I dont think it is just on the phono but I will confirm that? by switching to tape or something? As long as I have my amp on its there everytime. The real problem is I dont have a Tuner hooked up? Seriously I dont even have a tuner in the house! Could my speaker wires be acting as in attenna? and the amp amplifing the signal? Its odd that it is ownly one channel? or is that a sign that maybe it is a tube? Please can someone help as on very quite pieces of vinyl it's disturbing when you hear a radio station in the middle of say Chopin Etudes! I'am using a home built 2A3 amp and a MC cartridge if that matters? Thanks Daren |
As noted above, it is an absolute "must" that you use shielded cables. Also, if you have your cartridge "unloaded" (e.g., 47kohms or higher) you might try a lower figure (higher loading), such as 1,000 ohm or 150 ohm, etc. Higher loading attenuates high frequencies that may be overloading the phono stage or otherwise causing it to act up.
A friend had this problem with a Transfiguration Temper V cartridge, but not his Lyra Titan, and the difference was the lower source impedance of the Transfiguration cartridge. The Hovland preamp he was using has a factory default setting of 100kohms. Choosing a lower setting (higher loading) cured the problem. |
The various suggestions that have been made are worth a try. However, let me note that low impedance/high current circuits, which means a MC pickup and solid state amplification, are less likely to have your problem. |
Thank you all for your suggestions -- the "military" one is excellent. It turns out that I have some mu metal (the contents of one's garage are sometimes rather curious), and I can have it cut to fit the walls of a box that will cover the phono stage, not exactly beautiful, but the phono section is hiding in a cabinet anyway, so it won't matter. I suppose I could allso use an old wire cage that once housed a pet rabbit -- another long story. One wonders whether Faraday would be amused. |
Rives...For many years I used shielded 300 ohm twinlead for FM signal. I am in a weak signal area, and noise from autos on the nearby road was a problem. It worked very well, but the surprising thing was that the shield was, by design, not tied to ground at either end. It was floating. |
Another way (military practice) is to take a broom and clean RF off...:-) |
You might get lucky with changing tubes or cables, but it's unlikely and it's just a chance. The best thing is to shield the phono stage. There are a variety of ways of doing this. Most RF can be shielded by a wire cage that is tied to ground. There are other shielding materials such as "mu" metal that are also very effective. I had the same problem in one home and was successful with a piece of mu metal above and below the unit. The best shields enclose the unit entirely, but just like an antena that works best at a certain location, shielding can often be "incomplete" and still get the job done. |
Have you tried different lenghts of cables? The interconnect may be the proper antenna length for your local radio stations. |
RFI can come through your windows and changing cables (or wrapping them) or tubes may do nothing. You might just try turning the amp 90 degrees to see if it changes anything (but it's unlikely)
I used to live in a location with bad RFI - different radio stations from each speaker! - and the way I ended up solving the problem was to locate the stereo in the part of the place that was below ground level (and no windows either) and have the speaker cables come up through the floor. It worked beatifully. |
I live in an area prone to RF interference, and I had problems with my previous preamp, a Copland tube model. It picked up taxi radios, among other things. When I switched to a Klyne SK-5a, the problem went away. It could have been the Copland's design, or it could have been the tubes. |
What is your specific equipment and how close to a radio station tower do you live? |
|
