Cable quality and radio interference

[EZchair Picker]

I live within less than a mile of a major AM and FM radio station. When playing at church(which is closer to the stations), I've been picking up radio big time. After unplugging my guitar cable from the PA system, the radio station went away....which leads me to supect that it's the cable which is picking up the interference. Thing is, I'm using gepco x-band cables which are supposed to be double sheilded to prevent this type of interference. The pastor told me that he had tried several higher end cables before and had the same problem. When he switched back to the cheapies...the radio noise disappeared. So are higher quality, low capacitance cables more suseptable to this? Is it some brands but not others? I'm going to take my old cables to next rehearsal and see if that cleans things up.

[eddie27]

Don't know if you are using OD or fuzz, but this is what Analogman says about radio interference:

Radio Noise

My pedal is picking up the radio and I dont know what they are saying because it's Portuguese or Russian. How can I stop this?
Radio Frequency Interference (RF IF) is a tough one, most gain pedals like Fuzzes and even some wahs have a lot of RF problems. Since we cannot duplicate the problem here (it has no noise here) it's not something we can fix at our shop.

Gain is amplifying the RF from the air like a radio, it is tuned to the local station. Sometimes shortening wires or adding ferrite beads will help but since we dont have the problem here we would only be guessing. If you have a good tech he can try shortening the internal wires one by one and test to see if that helps, or he can try adding more and more ferrite beads and see if that stops the noise.

Also you can try to add a small capacitor on the input of the board or the input jack to ground, that often kills the noise. Try something small like 100pF then go bigger up to .01uF if needed. We often put a small cap right on the switch from the TO BOARD wire connection (gets connected to input jack when ON) to the GROUND connection.

Also dirty jacks can cause RF interference, try cleaning them with a swab and some contact cleaner.

A customer wrote :
One thing I did was to uncoil all the power leads in the back of the rack. I had them coiled up pretty tight and then cable tied. This immediately helped, but I wasn't completely satisfied.

At this point, I noticed that to make the radio signal be it's worst, touching the audio plugs on the back of the power amp (Metal sleeves) would do it.
So next I soldered some 4.7pf capacitors across the DC connectors on my pedals.

another customer with RF problems with a sunface wrote:

Thanks for the note, Mike. After applying an, ahem, no-too-low-tech technique it seems that the RF IF problem is gone. Get this: after reading your reply I got to fiddling with the guitar cables in the chain, which includes a Framptone Amp Switcher in front of two amps. Anyway, I just swung the guitar-out cable from the Strat around from the front and behind my body and presto/change-o, the RF IF disappeared. No contact cleaner, no screwdriver, no solder. No BS.
Hope that helps, good luck!

[noredr2]

Gotta say, I wasn't excited to open up this thread. Looking to upgrade my cheapo GC cables and I'm in the exact same boat....live really close to major broadcast antennas, play @ a church that's just as close. I always assumed the radio was from my amp (just tubes being tubes), but after a particularly noisy day a couple weeks ago, I unplugged the input cable and checked for radio....and nothing. Been doing a bunch of comparisons since w/ my different cables, and it all seems to vary day-to-day. There's some interference guitar->amp, guitar->amp->board, and even just random cable plugged in w/ nothing on the other end. It's nice to know that in a pinch I could get the local weather, but seeing as how I was considering going w/ the Gepco XB20, I might need to look more.

Any input from the cable dealers on the forum?

[EZchair Picker]

I've noticed that some days are worse that others as well. I figure a lot of it has to do with atmospheric conditions at and given time.

It would be nice to hear from some of the cable gurus out there. I'm sure this must be a common problem that comes up.

[amz-fx]

The low quality cable has more capacitance (per foot) between the conductors. The higher capacitance means that it can leak off the RF interference, as well as some of your tone.

What's the first pedal on your board? Does the RF only occur when this pedal is on?

AM radio stations transmit with different power levels at different times of the day and that can account for some of the differences. Also, atmospheric conditions will have an impact on the propagation of AM radio signals, as you noted.

regards, Jack

[cram]

isn't this just a matter of reducing factors?

Things I would try to see where the interference is -

Start from full setup (all connections you planned to use - pedals etc).
At each point verify the interference is/is not there
Remove one pedal (if there), repeat.
Once down to only cable - amp/pa, plug the shortest cable you can find in its place.

There are so many pedals, shielding, grounding, neighbors with whacky radio dreams, and friends with metal plates in head that come to mind as possibilities.

[noredr2]

Originally Posted by cram

isn't this just a matter of reducing factors?

Things I would try to see where the interference is -

Start from full setup (all connections you planned to use - pedals etc).
At each point verify the interference is/is not there
Remove one pedal (if there), repeat.
Once down to only cable - amp/pa, plug the shortest cable you can find in its place.

There are so many pedals, shielding, grounding, neighbors with whacky radio dreams, and friends with metal plates in head that come to mind as possibilities.

I've gone through this entire process, and the only time I'm not getting stations is amp on, nothing plugged in. Granted, there's times when I have to turn the amp up around 3 o'clock to get stations, so I've learned to live w/ it to some degree.

Originally Posted by amz-fx

The low quality cable has more capacitance (per foot) between the conductors. The higher capacitance means that it can leak off the RF interference, as well as some of your tone.

So Jack, it sounds like you're saying that for some of us unfortunate enough to live in the shadows of those ghastly antennae we just have to kinda suck it up, in tolerance and in tone, because lower capacitance cable is actually going to accentuate radio signals for those 12 (or 5 or 18 or whatever) hours a day when they're broadcasting and the clouds are just right?

Thoughts from others re: cables w/ RF shielding and interference issues?

[EZchair Picker]

Originally Posted by cram

isn't this just a matter of reducing factors?

I can't reduce it anymore than cable->DI box= am/fm radio stations.

I only use an accoustic electric, although I have recently picked up a DP500 modeler to play electric. Regardless, it happens just with the cable plugged in by itself. I'm going to take a few different cables with me Wednesday night to see if I can eliminate the problem with one of them.

amz-fx....I want to make sure that I understand what you're saying. Do I have it right in thinking that lower capacitance cables pickup and transfer the RF interference because they are so efficient where as higher capicitance cables do not as much because of how they degredate the sound quality comming through?

[cram]

Originally Posted by EZchair Picker

I can't reduce it anymore than cable->DI box= am/fm radio stations.

Ok - can you take the rig somewhere else?
Another electric power supply?
Another house, etc...

[EZchair Picker]

Originally Posted by cram

Ok - can you take the rig somewhere else?
Another electric power supply?
Another house, etc...

I'm plugging into the church's PA system. As soon as I plug the cable in (I have 2 10' Gepco X-band cables and it happens with both of them), I get instant radio. I'm not sure I'm following as to what I should take elsewhere to try?

[cram]

Alright - I misread. I thought you were dealing with your own amp and could port it to another place to test. That's all.

Do you get radio with only the cable (not guitar) plugged in?

[EZchair Picker]

Yup, all it takes is plugging in the cable by itself.

[amz-fx]

Originally Posted by EZchair Picker

amz-fx....I want to make sure that I understand what you're saying. Do I have it right in thinking that lower capacitance cables pickup and transfer the RF interference because they are so efficient where as higher capicitance cables do not as much because of how they degredate the sound quality comming through?

The higher capacitance cables divert the radio frequencies to ground due to the internal capacitance between the conductors, which keeps it out of the circuit. It may or may not cause an audible tone loss, depending on the cable.

There is also the possibility that the RF is getting into the circuit via the power supply connections. Most modern pedals have adequate filtering to keep that from happening but older pedals do not have power supply capacitor filters since they were designed for battery use only.... modern clones of some of these designs can let in noise and hum from the power supply and its cables.

While your cables may be great, the guitar likely has unshielded pickups, which may be where the radio is getting into the signal path... and then the pedals add gain to make it more evident.

The most important cable is the one that goes from the guitar to the first pedal. That cable ideally needs to be foil and braid shielded.

Another technique is to use two conductor shielded cable - the signal and its ground are connected to the two conductor wires while the shielding braid is connected at one end jack only. The other end of the braided shield is not connected to its jack. You then try the cable with the braid/shield end plugged in the amp (pedal) and see if that helps. Switch the cord around and see if it is better the other way. Proco Linecable is an example of this.

I like soldered ends better than friction fit, which has become popular. It is possible for corrosion to form on the unsoldered wire ends, which can act like diodes to rectify the AM radio signals (just my pref).

regards, Jack

[cram]

Originally Posted by EZchair Picker

Yup, all it takes is plugging in the cable by itself.

Closer stiiiiiiiill...
Do you have a 1/4' jack that you can plug in there without a cable.

The previous poster pointed to grounding issues with pedals. It can happen with amps as well.

Other questions to isolate - do other people plugging into this PA have the same problem, or is there any other input on the amp?

FWIW - in my apartment living days I went through many itterations of this with a couple amps. At times, this would just happen. And it would be accented with oscilation from a wah pedal or feedback distortion/drive.

[EZchair Picker]

Originally Posted by amz-fx

There is also the possibility that the RF is getting into the circuit via the power supply connections. Most modern pedals have adequate filtering to keep that from happening but older pedals do not have power supply capacitor filters since they were designed for battery use only.... modern clones of some of these designs can let in noise and hum from the power supply and its cables.

Originally Posted by cram

Other questions to isolate - do other people plugging into this PA have the same problem, or is there any other input on the amp?

I mostly play an acoustic electric straight into the PA, so there's not much I can do about sheilding there. Otherwise, I have just started using a digitech RP500 modeler for some electric playing, so I could see where grounding might be an issue with that. However, there are 2 other guys who are using Line6 Pods and they don't pick up the radio stations!! I don't use any other equipment than that (no amps or pedals).

Originally Posted by amz-fx

The higher capacitance cables divert the radio frequencies to ground due to the internal capacitance between the conductors, which keeps it out of the circuit. It may or may not cause an audible tone loss, depending on the cable.

I'm going to take some of my old/cheaper cables tonite and report back on the results. I'm hoping that they will help, if not solve most of the problem based on my understanding of what you've said.


Thanks for the help and info guys!