Noise from DC Power supply

[jgauthier]

Hello everyone,

At my place of work I have a paging system. The paging system itself basically just accepts audio. So it's powered, and powers the speakers. We've switched phone systems, and the new interface requires a device in the middle that basically connects the phone system to the paging system. This is not all that relevant, but I'm laying the ground work.

So, this device is a Bogen TAMB2. "Telephone Paging Access Module". I purchased it with a 24v power supply.
After attaching the paging system, and the power supply I have an awful buzzing through the speakers. I spoke with their technical support who said that the buzzing is almost always the power supply just passing noise through. So, I hooked up the power supply to a butt set, and I hear the same buzzing, although quieter.

Short of randomly purchasing replacing the power adapter until I luck out, does any one have any suggestions on reducing the noise?

I appreciate any suggestions!

 

[Harald Kapp]

Try a battery instead of the power supply to find out whether it is really the power supply or another source of noise.

What's the frequency of the buzzing? Is is mains (60 Hz)? Then there are basically two possibilities:

1. the power supply has very insufficient suppression of the mains frequency (in my view unlikely).
2. there is a ground loop that induces mains frequency noise to the audio circuit (should vanish when battery-operated).

To urther analyze a possible ground loop and find a remedy, look e.g. here or here (search keywords: "eliminate audio ground loop").

Harald

 

[jgauthier]

Great idea. I will try a battery! I was doing some research on the ground loop theory this morning as well. I will read the links you sent.

 

[jgauthier]

I was able to power this from a pure DC 24v DC source, and there wasn't a buzz. I will explore the ground loop issues, which sounds intimidating.

 

[Nasif Ahmed]

Hi Igauthier,

Did you try to explore the ground loop issues.
How did you overcome this issue.
Very strange that the TAMB2 does not have grounding options on the chassis itself.

 

[jgauthier]

Nasif,

Since I worked for a company that deals with cabling, I was able to talk to an engineering product manager who happened to have a device that eliminated ground loop noise. I put it inline with the power source, and it seemed to solve the problem. This was quite a while ago, so I'm foggy on the details.

 

[Nasif Ahmed]

igauthier,

i would be very thankful if you could get me some hint on the product or circuit.
Tired of googling to get an solution online.
Did you make any grounding to TAMB2 itself or did you try connecting the ground from the PBX to TAMB2.

Any small hint would be very helpful.

 

[BobK]

Ground loops in audio gear usually happen when the source and the amplifier are powered from different AC outlets. The problem is that the two grounds are at slightly different potentials due to the current flowing in the various wiring. If this is the case, try powering them from the same AC outlet and see if it goes away.

If this does not work, you need a transformer between the source and the amp in each audio line. These are sold for exactly that purpose. They work by isolating the two grounds from each other.

Bob

 

[Nasif Ahmed]

HI Bob,

First of all heartily thanks for your concern.
The issue is similar to "igauthier" reported scenario.
I have a Begen TAMB2 paging access module kept in between an IP-PBX and the sound system.

Whenever we make paging over loudspeakers, the voice is clear initially but when we hung the call there is small buzz heard over loudspeakers.

All are powered through the same power source. For powering ON the TAMB2 we use 24V DC power adopter plugged into 230V AC source. I heard a small humming noise through the test speaker from the 24V DC power adopter when tested with my telephone testing but set.
I just want to eliminate this humming noise up to some extent that it is not audible over overhead speakers.