Beolab 4000 -- hiss from speaker

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soundproof Posted: Tue, Nov 9 2021 6:25 PM

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Hi all, 

I have a pair of MkI Bl4000 that have worked perfectly. One of them now gives a low hiss (static noise) when on (connected to a Beosound 3000).
Does the same when not connected.

Have tried switching Beolink connectors, have also used the RCA-IN from another source. Speaker activates, but has the same background hiss.

Any suggestions? Easy cure or major repair? 

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soundproof replied on Fri, Nov 12 2021 1:41 PM

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Can't be this simple?

I opened up the speaker and noticed that there's a small metal strip of copper under the center screw located under the bottom of the aluminum plate. This strip is held in place by one of the fastening screws, but is not connected to anything.

Pondered and realized that it was laying flat against the plastic foundation. Studied the underside of the aluminium plate and saw a scratch mark where the strip would have been, if it wasn't lying flat.
I bent the strip, so that it would lie against the aluminium plate when I repositioned it, and fastened the plate.

Connected the power chord and hiss was gone. I had been "looking forward" to going into the board to remove foam rot, etc.,, but the speakers were great looking, so no problem there. Cold in Norway, so I take that foam rot not as prevalent as in warmer climates.

At any rate. The hiss is gone. Does the strip connecting with the aluminium plate, and the screw then connecting with the circuit board beneath, have a grounding purpose? Or were I just lucky here and the strip has no such purpose? 

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AlfJ replied on Wed, Dec 1 2021 7:45 PM

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Hi,

Just ran into something similar.
Are your speakers staying healthy? I hope so!

I tried your trick with that metal strip, but no success in my case. It looks looks like some kind of grounding strip, but can´t figure out how it connects to the rest of the chassis when the screw goes into plastic.

You may want to follow this thread https://archivedforum2.beoworld.org/forums/t/49976.aspx if the hiss comes back. No useful answers yet, but who knows what will come

Regards,

Alf