The Beomaster 4000 was B&O's most powerful receiver in 1972, at 60W per channel. Still, I don't think this one should be humming. I can feel it vibrating in my hands and it is making a very audible noise. This happens after it is switched on for a while. It doesn't seem to be putting out excessive heat. What's causing the vibration/noise?

is the humm coming from the speakers? if so is it like a 50hz humm, could be the smoothing capacitor beoming faulty.

Most likely the transformer itself. Unfortunately, that's very common.
The Beomaster will play along nicely, it's just annoying.

Martin

I just picked up a really nice looking Beomaster 4000. It has the humming issue being reported. Do you have any more information about the problem?  Is it usually a problem with the transformer? 

I noticed this about the humming problem -

When I plug in the Beomaster 4000 but still have the unit power switch turn off, I can feel a very faint vibration in the chassis.  Plugging in headphones I can hear a low level sound.  It isn't a buzz but it isn't quiet as you would expect.  Unplugging the Beomaster will make the low level sound go away.  It drops off gradually...due to the capacitors I suppose.  I tried connecting the receiver's chassis ground to my house ground but it had no affect on the vibration.

With the Beomaster plugged in and with the unit switched on, I can hear and feel the vibration in the chassis without any speakers (or headphones).  Music from an external source or the reciever's tuner seem to play fine.

I am planning to look for a replacement transformer (from a "parts" Beomaster 4000) but I am wondering if there are other components that could be contributing to the problem that I should check first.  It is curious that the vibration (although faint) begins as soon as the receiver power cord is plugged in even though the power switch is off.

Any ideas would be appreciated.

Thanks, sonavor 

"When I plug in the Beomaster 4000 but still have the unit power switch turn off, I can feel a very faint vibration in the chassis"

- That's a capacitive coupling. Perfectly normal, and most of it will probably disappear if you rotate the mains plug 180deg.
However, there will practically always be a little bit of this present, regardless of the phase. Particularly if you slide your fingers over metal parts.
Nothing is powered if the Beomaster is switched off - if the mains switch is working, that is.
Make sure it switches off properly.

Martin