Customer has couple of old Bogen horns in a mechanics shop. Amp is a TPU-35A. There is a WMT-1A matching transformer between amp and phone system (Avaya BCM50).

During a page, you hear the audio, but also some noise. Customer described it a being under water. To me, it sounds like the amp might be overdriving the horns. Settings are the same as always. I even turned down the main volume control. Without a page, you can hear a slight hum. Could it be wiring that is common to both horns? I don't have a spare amp to try. I'll have to listen to the output of the phone system with a butt set to see what that sounds like. I think those amps are generally pretty solid.

Thanks.
Jim

You could try hooking up one of the speakers directly to the Amp (eliminating the other speakers and all plant wiring) and see if there's still noise.

Sam

The very last thing I would suspect is the wiring. It's an inanimate object.

In addition to what Sam said:

Disconnect the amp input from the system. Do you hear hum? > replace amp.

Listen to system output with your butt set while disconnected from the amp.

If you are going to do this kind of work and charge for it you should have the proper test equipment. A signal generator and spare amp with speaker (and knowing how to troubleshoot with them) will find the problem in minutes.

-Hal

Generally for an existing system the cable doesn't change except for:

Construction or repair — Any workmen in the building recently?
Any new equipment or cabling of any kind? (Telephone, Data, Electrical . . .)

Was UTP used as speaker wire? If it's used on talk-back speakers may lead to higher electrical noise.

Be sure to check for proper AC grounding using a 3 Wire Receptacle Tester. It's not, hopefully, your responsibility to correct AC wiring but verifying your receptacle is properly wired and eliminate hours of searching for ghosts.

...and of course all the things Hal stated.

Loose or corroded connections in the wiring will cause noise. I agree it's the least likely of all scenarios. But really, what have you got? An Amp, Speakers, Wire and a Source (mic, telephone system, music source etc.)

Anytime I can eliminate 25% of the potential problems, easily, I do it.

But then I'm lazy and old fashioned.

Sam

Thanks for all the pointers. I was on-site today.
- Electric outlet is wired correctly, according to the receptacle tester.
- A normal page is understandable, but you can hear a distinct distortion.
- Input level setting is at normal setting, where it has been for years.

- Monitoring with a butt set on the input to the amp, amp disconnected, sounds very clear.
- Monitoring on input, with amp connected and still clear.

- Monitoring on output of the amp, while idle, and I can hear a small amount of hum. Same hum on the horns if it's quiet in the shop.
- Monitoring on output of the amp, with the cable to the horns disconnected, and the hum gets much louder.

So, I'm thinking there is something in the amp going bad? It's a Bogen TU-35.

Thanks.
Jim

Sounds like the amp is dying. Replace the amp.

-Hal