I am experiencing radio station transmissions coming through my sound system. I placed some capacitors across the inputs and it seemed to be a little better for a while. Now it's back with a vengeance. Any suggestions would be greatly appreciated.
Your fairly generic complaint of RF interference (RFI)in your as yet undescribed sound system is common for many users. The typical things you would do are to try to isolate the entry of the RFI by disconnecting equipment 'till the RFI goes away; starting with input sources (mics, line equipment, etc.) and progressing down the signal path. The suspect equipment or cable can be repaired or replaced as required.
In general, attention to details such as usage of balanced cabling of high quality, professional sound system components, and proper AC power interconnections will be your best preventive strategy.
Registered: 04/07/01
Posts: 16767
Loc: Madison,TN, UNITED STATES
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With all due respect, why do I keep hearing people suggest "checking equipment down the signal path?" What a waste of time.
A teacher of mine in college forced us to figure out that you need to split the signal chain in half. Whether or not the problem is still present, you've eliminated HALF the potential sources in 1 try. Guess what? You continue doing this until you have the source. In series paths (that is, linear) this will always save you time. (and money if you rely on getting things up and running quickly!)
Registered: 10/30/01
Posts: 5
Loc: Cambridge,MN,UNITED STATES
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I'll save the "divide and conquer" advice for the technicians reading these posts. Your average Joe Gigger has fairly short signal chains and can do the isolation any way that logically suits them.
Registered: 02/01/01
Posts: 17
Loc: Bloomington,IN,UNITED STATES
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Here are some places where I have encountered this:
- An electronic drum kit gave RF interference until we lifted the ground on the direct box.
- An electronically amplified acoustic guitar with a low battery became susceptible to RF interference.
- Check your connectors. An oxidized one can make a cable RF sensitive.
- Sometimes if a cable is exactly half a wavelength long (or an odd multiple of half a wavelength) it becomes supercritical, and makes even a well shielded amp act up. Changing to a different length fixes this.
Now for cures:
- Changing the ground setting on a direct box can eliminate a ground loop pickup or an isolation pickup.
- Look for ground loops and eliminate them. Effects loops are a common cause of this.
- Radio Shack sells the 273-105 RF choke that snaps around the suspect cable and traps RF emissions.
- Sometimes RF can come in on the power lines, or the output lines.
