My phone system is giving feedback through my speakers....
Apr 28, 2006 at 5:40 PM Thread Starter Post #1 of 2


Headphoneus Supremus
Jan 17, 2004
Not sure if this is the correct forum but since it's affecting speakers, I thought it might fly with the mods.

Here's the dilemma. I've got a generic office speaker system in my office. These are the round/white speakers commonly seen in hung ceiling tile. In addition, I have a multi-line phone system which uses a battery. For some time, I'd been hearing a buzz come from the speakers. In my business, there are numerous possibilities for feedback so it has taken some time to figure out where the problem was coming from. I've finally confirmed that the problem is feedback from the battery for the phone system. The battery info:

Valcom Model VP-4024B
Input 117V 60hz AC 150W
Output -24DC 4Amp Regulated A Battery. there some sort of filter that I can use on something like this to prevent the feedback?
Apr 29, 2006 at 4:48 AM Post #2 of 2

Uncle Erik

Uncle Exotic
Mar 18, 2006
Well, I don't think you have a problem with feedback. Feedback is best known as the sharp "ringing" sound you get when you hold a microphone too close to a speaker playing the output of the microphone. We've all heard it. What's happening is that putting the mike close to the speaker causes a loop or "feedback" between the two and you get that awful sound.

As for your problem, I'm not sure that's a battery you're dealing with. From what you listed, it sounds like a power supply. I'm not sure why it calls itself a battery, either.

What you're hearing is probably one of two things. First, the power supply might not be correctly rectifying the AC into DC. If you pass AC, you will hear the 60Hz hum of the power line. Fixing this might require a new power supply or rebuilding it. The other possibility is a ground loop. A good discussion of finding and fixing ground loops is found here:

Good luck- let us know how it turns out.

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