I am in the process of setting up a theatre surround sound system.  My query concerns the audio side.

I have a Denon 1909 AV receiver that only has speaker level outputs.  The three front speakers and two surround back speakers are passive and work perfectly.  My two side speakers are B&O Beolab 6000s, which are active.  My particular query concerns these two speakers.

The cable between the receiver and the speakers is a high quality Ecosse two core cable.  However as this cannot be terminated into the speaker I have to make a joint to an RCA phone plug.  The little bit of cable connected to this plug (0.5 metres) is single insulated core and an uninsulated stranded copper.  Both covered by the overall PVC over sheath.   The core is connected to the plug centre pin and the stranded copper to the other phone terminal.  This is then connected to the two core speaker cable running from the Denon.  The Beolab 6000 is connected via the phono plug and the speaker switch,  R  L  & Line, is switched to line.  This is as instructed in the speaker handbook for using it with non B&O equipment.

When the Denon AV receiver is switched on and in standby mode, the Beolabs sit there also in standby mode with a green light showing and a humming noise.  When I commence playing a source through the Denon, the speakers works perfectly.  When the source stops, playing the speaker sits there with the green light on and then switch to standby after two to three minutes showing the red light exactly as expected.

However, when I switch the Denon AV receiver to standby or off the two Beolabs hum loudly until I switch off the power feeding each speaker.  The same applies if I switch them on when the Denon is switched off.  

I am a little baffled as both speakers work perfectly (apart from the loud humming as described which I have to solve).  This is most odd as I am putting amplified line output into a speaker, which is only suppose to accept line in.

Can anyone give some advice on how to get rid of the hum other than switching the speaker supply off every time it is not in use?  I have tried a few things but have been unable to solve the problem.  Would a power Line out/to RCA line in converter assist?  I feel it could be an earth loop problem but then I think it could be something to do with a speaker level in to a speaker that only, I believe, accepts preamp signals.

Summary of tests.  Light condition refer to the light at the base of the Beolab 6000s.

(1)     Denon switched off,  speakers switched on  - Speakers hum green light on.

(2)     Denon swithched on to standby, speakers switched on – Speakers hum green light on.

(3)     Denon switched to source, speakers switched on – Speakers play perfectly no hum.

(When the source has finished playing the speakers switch to standby about 3 minutes after playing – light red).

(4)     Denon switched to standby, speakers switched on – Speakers hum green light on

(5)    Denon switched off and power plug removed, speakers switched on – speakers hum green light on.

Above conditions apply to any source used.

I look forward to any responses received.