I get a pop when I switch on if the speaker switch is on - but not if it is off. If I then switch the speaker on, there is no pop.

how much time do you wait before you switch on the speakers?

A couple of seconds. My 4400 does much the same.

Doctor wrote:

I get a pop when I switch on if the speaker switch is on - but not if it is off. If I then switch the speaker on, there is no pop.

Me too. Martin serviced mine for me, and I assume this is normal. I just turn the volume down when I turn it on to keep the pop to a minimum.

It is totally normal, and quite loud.  I have a perfectly restored one from Frede, just a few months old now.  I confirmed this with Frede.  Here is his reply about it:

"The ‘start noise’ of the Beolab.

YES, this is normal – all Beolab 5000 are designed that way and another point – all amplifiers designed during the 60’s and beginning of the 70’s  have the same ‘feature’.  "

Yes, it's normal for all B&O single-supply amplifiers where the output stage has a large
capacitor in series with the loudspeaker, which in turn is connected to ground, to isolate the
amplifier DC from the speaker.

The pop comes from current running through the speaker as one side of the capacitor charges up
to about half the supply voltage.

You can switch off the speakers at power up to eliminate the pop but some B&O's will still
give the pop when you then switch on the speakers later since breaking the speaker circuit using
the switch will also keep the capacitor from charging.
Some have an extra bleeder resistor mounted to minimize the problem but it doesn't cure it completely.

Occasionally the same problem exists at power down but it's rarely as loud.

Martin

Played with mine again last night . Keeping the speakers swityched off reduces the pop but does not completely eliminate it when speakers then switched on. Never really thought about this before as it has always done it! I did read a review of the 4400 in which this 'feature' was criticised by the reviewer.

And I just tried with my 5000. If anything, the speaker switch exercise made the pop worse.

The 4400 is actually different in this respect as it has DC coupled outputs. I believe the pop on that design comes from the power supply voltages and perhaps preamp stages coming up at uneven rates. On those, a delayed speaker relay would eliminate the pop. Note that Speakers2 will usually pop even on the most recent Beomasters!

Anyway, I've always thought it to be just a nuisance. All the energy will be in the lowest frequencies, and the speaker woofers can take it without any danger.

I've lent a BM4400 + CX100 + Cona setup to a friend of mine. On that, the startup pop is more like a boom 😁

When I connected an active Genelec subwoofer to my (at-work) Beomaster 4500, I soon learned to switch the sub on AFTER switching on the Beomaster! It made "quite a" boom at startup 😂