RCA cable static noise

[Zbach]

I bought a Q-See security camera system. Theres a RCA audio out on the DVR so you can remotely talk through a powered speaker in the home. There is a constant hum when speaker is on. I tried different cables and the speaker works fine without the DVR. Is there anything that can condition the signal from the single RCA cable?

 

[Alec Mowat]

Not an expert, but you are getting interference from somewhere.

Anything wireless near by?

 

[skit75]

It is an unbalanced analog output. You can try a short cable but anything longer than say about 6 feet and it will begin to act like an antenna picking up who knows what.

 

[Zbach]

No. The system is in the garage so its away from everything.

 

[Zbach]

I tried a 3 foot cable right next to the DVR just to make sure it wasn't the long run of cable but it still made the noise

 

[Alec Mowat]

Is there an electric garage door opener?

If you have an android app, there are some handy programs that use the wifi antenna to identify high frequency sounds and Wifi bands. Might be useful.

 

[skit75]

The source of the hum is probably from the the DVR power supply then. You can try to power the DVR through a UPS with surge protection/suppresion & AC voltage filtering but it still might hum even after that. It could just be a bad/noisy output on the DVR as well.

The powered speaker doesn't hum when you connect it to another source?

 

[Zbach]

No, speaker works fine on other sources. I have the DVR plugged into a UPS with surge protection. Is there any kind of isolator that would fix this?

 

[Shaun o]

What it means is if the Dvr has an internal power supply it is electromagnetic interference.
Because the internal transformer is no shielded enough.

And why you get humming. or another amp or device with a power source is sitting on top or close to the Dvr recorder and the transformer in it is not shielded enough. So you must move any other device using power away from the Dvr.

Or that you have a bad ground signal on the Rca port of the Dvr.

If the speaker works fine with another RCA output.
And no other device is close to the dvr then you have a bad ground on the Rca of the dvr.

You can test this by touching the metal case of of the dvr bare metal not painted. And the hum from the speaker will get louder or more quiet.

Because your body caries a small amount of static current.
And will discharge to earth since the outer case of the dvr should be earthed.