Hearing Radio, Swapping Speaker Wires Resolves

Hi all,

I’m having an odd issue for which I’d like to solicit your thoughts. I receive a faint radio transmission on my right speaker channel. The signal is louder at night. If I instead terminate the wire (fed from the right channel output) to the left speaker, then the radio transmission follows the wire.

So the issue is up-line, right?

Here is where it gets weird. If I swap the wires completely between channels (such that the wire that was serving the right channel is now on the left and vice verse) then the radio signal disappears.

I’ve repeated this many times over the last week.

The issue began after I moved the speakers to the opposite wall of my room, but left my components on their wall mounted shelves. To do so, I ran about 11 meters of 10 gauge ofc under the floor. For a while I had this wire jacked straight into the speakers without issue. The problem was introduced when I terminated them into a wall plate and hooked them up with my “previous” wires.

The wire that was “picking up” the radio when sourced from the right output is quite a big longer than the other (6 meters versus 3.)

The following describes the signal path.

Luxman CL-38 uC
Luxman MQ-88 uC
(About) 11 meters of 10 gauge ofc (hard wired to amp, terminating mechanically at the other wall.)
The speaker cables (Kimber 8TC)
a pair of Altec A7’s

Finally, the radio transmission is still audible when the pre amplifier is turned off.

Thanks!

 

Tell us a little bit more about this wall plate and previous wires. How about taking each one out of the chain and checking if you hear any difference.
The long wire is surely acting as an antenna but we need more info to determine why you did not have the problem even when the long wire was hooked straight to the speakers v/s thru the wall plate and other patch/extension wiring.

 

Might try slapping a ferrite choke around either the long line behind the plate or the speaker cable at the speaker binding posts and see if that works.

 

Yep, try the choke idea. Had something similar a few years back and shielding that cable in that case resolved my issue.

 

@Lobster Graham Funk
so were you able to figure this out ?

 

Kind of. As swapping the speaker cables that run from the wall resolved the issue, I left it alone. Until yesterday.

I borrowed 3 set of interconnects to play with:

1) Cardas Clear Reflection
2) Cardas Clear Cygnus
3) Transparent Super RCA

I ran them from the preamp to the amp.

Both the Cygnus and the Super RCA cables produce the radio signal (whether hooked up to the preamp or not.)

At this point I’m guessing that there is just some net equation of copper (whether in or out of the amp) that happens to work well as an antenna.

With an actual signal on the line the radio isn’t overwhelming (though clearly there.) If I mute the preamp though, it is very apparent.

Maybe my old radio shack cable and the Reflection are sufficiently shielded?

 

I went ahead and bought some ferrite chokes to place on the speaker wire run within the walls. Should arrive tomorrow (while I still have the loaner interconnects.). I’ll report the results.

 

the amp probably does not have that great HF rejection/filtering at the input/output. but in fairness thats not too uncommon either in tube amps.
does the amp come with a cage/cover or is it bare ? if no cage then you might want to look into a metal rf shielding cage for it.

 

The cage is on the amp.

 

The ferrite chokes didn’t help, fwiw.

 

Is the station you hear AM or FM? Do you know where the station is?

There are many different kinds of ferrite materials, they are not universal in how effective they are at different frequencies. For example, I use toroids made of Ferrite 77 for AM radio suppression, which has these characteristics. Other materials are not effective 1mHz, but are more effective at 100mHz. It depends on the material.

The specific product is here.

In application, I take the wire in question and pass it through the toroid then wind it back around so several turns of the wire are wrapped around it.

 

Well, there's a bright side here, at least you won't have to buy a tuner! You got two for one!

 

if nothing helps then contact the manufacturer. If your amp is still under warranty maybe they will do or suggest something to fix the problem.
In the very least, they need to know this about their (very expensive) product.

 

Interesting. For sure, the signal is very clear. It is an AM station (KEZW 1430 in Aurora, CO.)

The cables that you wound through the toroid, were they shielded?

 

Ugh, so KEZW is broadcasting within the batch of towers near my house (less than 3 km away.)

 

Have you tried really cleaning all the RCA plugs and jacks? Some tarnish somewhere can act like a diode (like an ancient cat whisker radio) and demodulate AM radio.

 

Just call the station and ask them to play the music you like. Problem solved.

 

KEZW is 10kW day and 5kW night, omnidirectional. You’re under 2 miles away, so you’re in a hot field but it could be much worse. Like 50kw. And there is audio gear working just fine at 50kw transmitter sites, so there’s hope.

There may be a lot of towers on that site but KEZW
only uses one.

I use the ferrite toroids on all types of cables, shielded or not. It increases the impedance to RF carried anywhere on the cable, and Each turn of wire you loop through it increase the effectiveness. Those thing are fairly cheap, and what I’d recommend you try next. There are other things to try too, but nothing quite as effective and easy.

One other thing is to make sure you have a good earth ground on the chassis of the offending amp. And that could take a bit of effort beyond just the third pin on the plug.

 

I did order the toroids that you recommended. I’ll update when they arrive.

 

Interesting regarding the earth ground. The MQ-88uc doesn’t use one (there isn’t a pin on the power line.)

 

You can always add a chassis ground, but don't get ahead of the problem yet. Try the toroids, might take several turns of wire, even more than one ferrite.

 

I borrowed more cables this weekend. High end speaker, RCA, and power. The power and speaker cables made no difference. The more expensive RCA cables pronouncedly brought out the radio signal (preamp to amp.)

Frustrated, I moved all the components to the other side of the room in order to remove the speaker cable running under the floor from the equation.

The radio noise resolved. I left if that way for several days before moving the gear back. Immediately the radio signal returned.

 

I received the toroids. I wrapped both the positive and negative channels of the left “floor cable” around 2 of the toroids (about 20 loops) near the amp connection. That resolved the radio noise and I was very proud of my self.

Much celebration was had until I noticed the degradation from the left channel. I put on a mono record and toggled between the left and right channels. The left channel sounded horrible. It sounded like it was was under water.

I flipped source inputs until the only variable remaining was the “floor” wire. I removed the toroids. Everything sounded great again.

In short, the toroids resolved the radio signal but the cure was worse than the disease.

 

If eliminating those wires from the system eliminates the RF interference, they are the problem.

How did you run the cables under the floor? Did you tack them up? Are they running together? Are they in parallel or in separate runs? If they are parallel, that might increase coupling. I tend to think they are not in parallel or else you'd probably hear the AM radio station in both speakers. Move those wires a bit (more on this below) with someone up in the room listening to the AM radio sound and see if it changes. Once you find a spot that changes the sound, you know where to start looking.

Even if you can't find a particular spot where there is an issue, you need to check that you didn't accidentally crush/cut the insulation on one or both of these wires. Sometimes, a metal hanging clip (a U clip), if hammered in too far, can crunch a speaker wire to the point that some of the wires break through the insulating jacket. Even if these wires don't touch ground or the other channel's wire, they can still be problematic. If the wires are hung with U clips, try pulling out all of the clips and let the wires hang. See if the problem goes away.

The next thing to worry about is how close these speaker wires are to any AC house wiring, particularly any junction boxes. If they run alongside AC wires, that could increase the RF coupling. Unusual, but not impossible. I tend to avoid close contact between speaker wires and AC wires to avoid the potential for 60 Hz hum (which most amps filter out anyway), but that is not what you're hearing.

If the experiment above (moving wires to see if the sound changes) does find a trouble spot, check what's around that area. Move the wire away from metal items like water pipes, pipe hangers, AC wires and especially any bare copper ground wires that are sometimes run for utilities like old telephone landlines or cable TV.

I'd also suggest that you could run the wires under the floor as a twisted pair, but I've never heard of that working at audio frequencies. It would also be tough to do now, as you'd have to unhook the wires from both ends and drop them under the floor, twist them together and reattach them at the ends. Twisting also uses more wire per foot, so your wires might not be long enough to twist them.

 

what happened about this wall plate ? did you rule it out as a source of problem ? are you still using it ?