The Workbench

Re: BM8000 Shutdown noise

geearr — Tue, 18 Nov 2008 06:19:04 GMT

Hi Martin

Thanks for the input. I actually intended to get both of the amplifier boards upgraded first as part of my refurbishing program, so the fact that this is an amplifier related matter is good news for me. I was a bit concerned that if it was a power supply issue, I might end up damaging any of the good work on the amplifiers. In the meantime, I'll just avoid hitting the mains switch too early.

Geoff

Re: BM8000 Shutdown noise

Dillen — Tue, 18 Nov 2008 06:07:12 GMT

Geoff,

This problem is caused by unstable running of the amplifiers as their capacitors discharge (unequally). A recap will probably correct most of the problem but it won't be completely silent everytime you disconnect the mains. A little thump sound from one or both speakers should be considered normal.

The same applies to most other B&O receivers with the standby function, like Beomaster 5000, 5500, 6000, 6500 etc.

I once had a BM8000 on the bench where one of the amplifiers started to oscillate everytime it was put into standby, producing a high pitch whistle in slightly increasing frequency from one speaker, very loud and clear, lasting a couple of seconds and ending in a thump sound. A recap of the amplifier boards cured this.

Martin

BM8000 Shutdown noise

geearr — Mon, 17 Nov 2008 16:42:45 GMT

Hi everyone

I have noticed that my BM8000 makes a terrible noise if I switch it off at the mains too quickly. Sounds like a capacitor discharging directly through the speakers. As long as I switch it to standby and then wait for three or four minutes there appears to be no problem and all you hear is the gentle click of the relays. However, if you switch off the mains too soon, you will most certainly jump to high heaven.

I will be starting the mandatory cap changing plan in the not too distant future but in the meantime, would appreciate some guidance as to the location and reason for this specific problem. Is it likely to be a power supply issue or an amplifier issue or what? Any ideas?

Thanks

Geoff