Hello there,
I'm trying to put some life back in to my 40-50 year old Bang and Olufsen Beolab 5000 stereo amp. Basically I've changed most of the caps in the output stage (not the ones in the feedback yet though), and I've been cleaner the potentiometers with contact cleaner.
I still get quite a high humming noise in the speakers when having the volume at 50% and upwards. Is it dried out caps, or should I be looking somewhere else?
I know it's a bit vague, but hope you can point me in some direction.
Thanks
Tore
I'm trying to put some life back in to my 40-50 year old Bang and Olufsen Beolab 5000 stereo amp. Basically I've changed most of the caps in the output stage (not the ones in the feedback yet though), and I've been cleaner the potentiometers with contact cleaner.
I still get quite a high humming noise in the speakers when having the volume at 50% and upwards. Is it dried out caps, or should I be looking somewhere else?
I know it's a bit vague, but hope you can point me in some direction.
Thanks
Tore
That could definitely be the problem. But how is it that it influences the output of the amp, if the caps in the power supply is dried it? There is three caps, two 50uF and one 80uF.
I'm not the a power supply expert, so I'm not entirely sure of their design purpose, but I've uploaded the schematic. The quality is really bad, but I can't find anything better at the moment.
I'm not the a power supply expert, so I'm not entirely sure of their design purpose, but I've uploaded the schematic. The quality is really bad, but I can't find anything better at the moment.
An externally hosted image should be here but it was not working when we last tested it.
i'd start with the 2500uF cap next to the 4 diodes after the transformer (dammit, terminology is failing me at the moment :s)
I already changed that, along with two 3000uF that are connected on the output. I have added the output stage too. Why would you put caps on the output like that?
An externally hosted image should be here but it was not working when we last tested it.
Hi Alaza,
I would guess that the output caps are there for protection: many years ago when I taught English to Danes in Copenhagen one of my students was an Old-Style electronics engineer. He swore blind that this kind of circuit could not work!
On a different note, I have just bought a set Beolab/Beomaster 5000 and I am looking for Circuit diagrams. Is there any chance you could send me those (off-list)
All the best
Frederik
(A Dane in Scotland)
[/QUOTalready changed that, along with two 3000uF that are connected on the output. I have added the output stage too. Why would you put caps on the output like that?
With single rail ps you will have half of the voltage standing on the output. So to save your speaker from dead by frying. It was normal in many amps back then
Did you follow the indication of post #8 and check out the preamplifier? A little logic should tell you that if you can adjust the noise level at the volume control, the problem is before it. i.e. preamp/tone controls, perhaps. I would look to replacing all electrolytic caps there but the problem may not be that simple. Some semiconductors can also develop faults which lead to increasing noise levels too but seriously, without test equipment and experience in taking measurements, we cannot diagnose a fault by guessing from a very general symptom like "hissing noise".
I'm not sure that the Beolab 5000 can be 50 years old, but definitely 40 years.
There was something very similar to this in the house of a school friend, but let me not give any more of my age away. It was very cool back in the day. Still is, now that I look it at again.
There was something very similar to this in the house of a school friend, but let me not give any more of my age away. It was very cool back in the day. Still is, now that I look it at again.
An externally hosted image should be here but it was not working when we last tested it.
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