Hey everyone, first post here but I have been poking around on the site for a while now. Sorry if this post is kind of long...
My church has had problems with picking up an AM radio station through the sound system ever since the building was constructed 7-8 years ago and the sound system was installed. I was not around when the church was built, but I am now trying to figure out the problem because it is driving me nuts. I believe the station I am picking up is about 20-30 miles away.
The AM signal is almost always there, sometimes we seem to pick it up a lot lot louder than other times. We mainly notice it on a podium mic that we really crank the gain on in order to be able to pick up people who speak quietly. Several other channels pick it up as well but it is virtually inaudible under normal gain conditions.
The snake is run through walls and not in any sort of conduit at all. The individual channels in the snake have a ground wire and a foil shield. The snake is probably about 150 feet long roughly. There is no shield over the whole bundle, just a rubber jacket.
The snake runs to the middle of the stage and from there explodes into a spaghetti mess of wires... none of the individual channel wires were cut to length when installed, or routed in any sort of reasonable way. I spent a couple hours under the stage and routed a couple of the wires that go to the stage box near the podium in the straightest route I could, I cut off about 20 feet of extra wire and soldered on some new Neutrik female XLRs to replace the original Whirlwind ones because they were getting loose. I thought for sure this would help, but if anything the radio got even louder on that channel after my attempt at a fix.
Multiple different channels on the snake seem to pick up radio, some worse than others. Most channels get some degree of radio, we do have a couple channels that seem to be perfectly quiet for some reason though.
I have taken apart some of the XLR connectors and examined the wiring. Pin 1 is connected to the ground wire, and the shell of the XLR connectors are not connected to pin 1.
I have disconnected pin 1 from the XLR going to the mixer on a few of the problem channels, and the AM is instantly gone. However, some of our mics need phantom power so that also killed some mics.
I brought in a different mixer for testing, a brand new Behringer that I was able to borrow for a day. I connected a problem channel from the snake to the Behringer and the only other stuff connected to it was the power cord and a set of headphones. I was still picking up radio, but it was definitely at a much lower level than through the Peavey mixer.
Connecting different mics to a problem channel makes no difference. Different mic cords make no difference. You can unplug the mic cord from the stage box and still pick up radio with nothing connected to that channel.
I have been doing some reading and it looks like there are two different things I can try... ferrite cores or small capacitors wired between pins 2 and 3 to pin 1 on the XLRs. Which should I try first? I assume that I should be doing these things at the mixer end of the snake, right? Or is there something else I should be checking into first?
Any advice would be appreciated.
I don't think this is an equipment problem, but I am listing this stuff just in case. If you need actual model numbers on the stuff I don't have here I can get them.
40 channel snake, switchcraft male XLRs connected to mixer, Whirlwind female XLRs in stage boxes
Peavey RQ 4332C mixer
Some sort of analog EQ (dual 16 band I believe, not sure how it is connected)
DBX DriveRack 260 crossover/limiter/etc
3 amps for main speakers/subs in rack close to mixer
1 amp for stage monitor installed under stage
3 main speakers and large sub suspended from ceiling of church in vertical array
1 wedge monitor on stage
A bunch of mics... Senheiser and Shure corded, Shure and Audio Technica cordless.
There are 3 rackmount surge protector type boxes that the mixer, amps, EQ, etc are powered from... I believe they are on 2 different AC circuits. The amp for the stage monitor is on a 3rd circuit.