Ive just been listening to my "new" pentas. They sounded really good at first, but when i turned them off and moved them after a few hours one of the amps began making a loud buzzing sound just like a large transformer does. This buzzing sound can also be heard from the speaker elements themselves, but not as loud as from the amp/ps.

The sound returns when i turn the speaker off, and turn it on again.

Could this be the sound of one of the capasitors on the amp or power supply dying? If so, where should I start replacing first?

The speakers are connected to a pre-amplifier through the line in port. I have tried disconnecting this line, and the sound continues until the beolab turn itself off.

I have not tried using the powerlink, since I don't have my Beocenter here at the moment.

I appreciate any input. :)

 
-Magnus
 

 

Update:

When I turned them on this morning everything was back to normal. This does support my capasitor-theory, doesn't it? 

Magnus,

When you switch them back on in the morning, how long does it take for the problem to start again ?

I noticed this yesterday evening so I haven't had the time to do much troubleshooting, but this morning i had them going for about 15 minutes without any problems before i had to leave for work.

Keith,

I have seen (heard?) this phenomenon with a number of sets of active speakers. Seems to happen when you connect the speakers when the mains is on and occurs with both line input and powerlink.

When the speaker switches to standby, either automatically in the case of line input or by manual application of red standby in powerlink systems, the problem goes away and never reappears until you connect them "live" again.

I always remind people to power down everything before altering connections. Howerver, I myself have been known to forget!!

Graham,

Now you have raised this point, I do remember something like this in the distance past. I will have to have a look through my old notes..

The sound/buzz returned again now, after about 1.5-2 hours use. I think it may be gradually increasing with time. It wasn't as loud as it was last night, but I may have noticed earlier this time.

This problem may be an earthing issue.

Are both speakers and pre-amp connected to the same mains power source ?

I'm back in my apartment now, and am still experiencing the same problem. The problematic speaker is connected a different wall socket than the beocenter and the other speaker.
 

So, the speaker giving you the problem is conencted to a different power point.

I suggest you swap the two speakers around and see if the problem follows the speaker or not.

I don't think that will make any difference, as I have now experienced the same problem in two different locations. When I first posted I was in my parents house, and now I am in my apartment 370 miles away.

In this forum thread: http://forums.audioholics.com/forums/archive/index.php/t-3879.html, a guy seems to have the same problem as me. I had a look at how the transformer was mounted in the chassis, and it sure is a tight fit. I suspect that both the glue holding the windings and the rubber feet the screws go through may have deteriorated with time.

I'm considering trying to coat the entire transformer in at thick layer of high-temp hot glue or epoxy to dampen the hum. Is there some reason why I should not do this? 

Well, I did not understand that the problem had happened in different locations.

I think you may be correct then that you have vibrating laminations and certainly you can coat the transformer with a resin based clue without causing problems.

Then I'll try that when get my new parts for the upgrade described in the "Beolab penta 1 revidieren" thread in the workbench-forum. :)

Thanks for your help this far, Keith! Your input is highly valued!