What do you think is causing this noise on the intercom?

[LesWilson]

We've been only using our Clearcom MS-400A base station once a year for our High School musical. I'd like to start using it more at our weekly assemblies but would like to address the hissing if possible. Below is a recording of the noise with an RTA visualization. The recording was taken from a headset connected to the base station. I also made one from an RS-100A beltpack but it's the same.

It's irritating and wearisome after a 2 hour show. I can replace components on a CB and am willing to give it a shot. What components do you think need replacing to clean it up?

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[brucek]

Wow, a RS100A....that is not a young beltpack. They also dont have the most quiet op amps in them. Depending on how old they are, the pcb may be completely glooped and not serviceable. It could also be caused by a noisy volume pot.

Does the hiss drop when you disconnect the lines from the main station? It could be failing caps in the main station....but I'm suspecting its just the sum of all the noise caused by older components. If you have the wrong impedance mics and ears in the headsets, then you can end up with a bad gain structure causing the ear level to have to be turned way up, increasing the hiss.

Good luck

 

[RonHebbard]

Wow, a RS100A....that is not a young beltpack. They also dont have the most quiet op amps in them. Depending on how old they are, the pcb may be completely glooped and not serviceable. It could also be caused by a noisy volume pot.

Does the hiss drop when you disconnect the lines from the main station? It could be failing caps in the main station....but I'm suspecting its just the sum of all the noise caused by older components. If you have the wrong impedance mics and ears in the headsets, then you can end up with a bad gain structure causing the ear level to have to be turned way up, increasing the hiss.

Good luck

And / Or if he's running unterminated, he'd have FAR too much gain and thus hiss and hum.
Toodleoo!
Ron Hebbard

 

[LesWilson]

Thanks guys. No hum just hiss. Everything works great except for the hiss and scratchy pots in the beltpacks and MR-102A wall stations. LOL.

I use newly refurbished Sennheiser HMD 281 Pro headsets (200 ohm mic, 64 ohm headphone) but the hiss has been there since I installed the surplussed unit in 2009. I thought by testing it at the base station, I'd eliminate effects of the wired runs. I was hoping it was possibly a couple components on the PCB. I'll check the termination switches @RonHebbard. Thanks.

 

[TimMc]

Contact Clear-Com. Sadly, Rom is no longer with us or I'd have suggested you talk to him.

My guess is the base station needs some capacitors replaced. As Bruce points out the RS100 is an old, old belt pack, too, but I think the primary issue is in the base station.

 

[LesWilson]

Yes I was hoping a Clear-com gray beard was hanging here. I ran into my TD and he said he was here when the unit was deployed in 1991. He remembered it as always having that hiss. To quote “It’s led a long noisy life” He added properly working modern ones won’t have the hiss.