Not earthed or what ???

[Soulhunter]

Someone asked me to help him to setup n' wire his new A/V receiver...

Considering that Ive wired dozens of cables @ my home, no problem !!!

But after everything was connected, there was a "humm" @ the subwoofer... :scared:

Afaik this happens when a component in the chain is not properly earthed !!!


After some time I found the reason...

It was the "antenna-box" (the thing in the wall where you get TV/Radio signals from) !!!

As soon I connected a component that was also plugged to the antenna-box (TV etc.) this "humm" was there...

And as soon I unplugged the cable(s) from the antenna-box the "humm" was completely gone !!!

Simple sketch...

http://img36.exs.cx/img36/415/simple2.png

So, is it possible that the antenna-box is not proper earthed ???

When yes, how to solve this problem... :confused:


Tia n' Bye

[TotalChaos]

The "hum" is no doubt line noise from the power wiring in this house. If at all possible try to keep some distance between power cords and signal cables. If the noise IS coming from inside the wall, then grounding/earthing the antenna box may not help. This would indicate that the antenna box is not properly shielded from interference.

This may sound like I'm trying to blow up your equipment, but you can connect a wire from the "third prong" on your power outlet to the antenna box (or anything else for that matter) to ground/earth said device. Some building code requires the "third prong" to be connected to a metal rod buried some 6 feet in the ground right outside the house.... hence the names grounding/grounded/earthed.

[Soulhunter]

The "hum" is no doubt line noise from the power wiring in this house.

Only for my own education...

Is this the reason why its only hearable at the subwoofer ???

Coz power wires run @ 50Hz and the Subwoofer can output 50Hz signals ???

This would indicate that the antenna box is not properly shielded from interference.

Would buying a new one help in this case ???

This may sound like I'm trying to blow up your equipment...

Fortunately its not mine... :D

...but you can connect a wire from the "third prong" on your power outlet to the antenna box (or anything else for that matter) to ground/earth said device.

To be sure, are this the (red) thingy's here...

http://img3.exs.cx/img3/1843/Unbenannt.png

Some building code requires the "third prong" to be connected to a metal rod buried some 6 feet in the ground right outside the house.... hence the names grounding/grounded/earthed.

Hmm, maybe I could connect it to the "heating pipes" then ???


Tia n' Bye

[TotalChaos]

Ooops!! I was assuming you lived in the USA. We use 60Hz here. Audio equipment generaly uses crossover circuitry which sends low frequency signals to the subwoofer. Your right... 60Hz/50Hz those are deff low pass frequencies.

I can't say much about your antenna box because I have no idea what your actualy useing.

Hmmmmmm...... I don't want to steer you wrong on the grounded prong thing. The outlets here have two blade style prongs for power and one round style prong for earth ground. (the crazy part is that one blade prong of our 120v outlets is actualy hooked to that same earth ground as the third round prong.)

If your house were up to code and you lived in the USA, you could use the pipes, phone distribution block, or cable distribution block for grounding.

If you want to get creative try wrapping any exposed equipment in tinfoil. (make sure you don't let the tinfoil touch the actual electronics of equipment... your basicly making a faraday cage to stop EMI from leave/entering your equipment)

[Soulhunter]

Originally posted by TotalChaos
I can't say much about your antenna box because I have no idea what your actually using.

The inner of the antenna box looks like this...

http://img56.exs.cx/img56/9343/282227_BB_00_FBEPS.jpg

So, a cable from the mass of each plug to a pipe should do it, no ???

__________________

Btw, someone else told a "Mantelstromfilter" would solve this problem... :confused:

Is someone from Germany here who knows what this thing does ???


Tia n' Bye

[TotalChaos]

For my education I looked up mantelstromfilter. This article seems to address your issue. http://www.siski.de/~carsten/mantelstromfilter.html

It looks to me like all you have to do is introduce a high frequency/high-pass filter (IE the capacitors/condensors) to purge the relativly low frequency Hummm your hearing.

[Soulhunter]

Jackpot, think its what Ive looked for... :)

Big thanks TotalChaos !!!


Bye