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Buzzing BeoLab6000

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moshejay
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moshejay posted on Mon, Nov 11 2013 2:29 AM

Hi there

i have a pair of beolabs 6000.

I plug one of them (doesn't matter which) into the AC wall plug & switch it on.

I connect a 2m RCA cable to the RCA connection on the speaker, and put the switch into phono setting...the other end of the RCA cable is not connected to anything. The speaker remains quiet.

I TOUCH the other end of the RCA cable & suddenly i hear a loud buzzing that remains there whilst i touch the end of the cable....
Q1) can anyone tell me why this happens??

Then, i get a 4m RCA cable and connect it just as i did with the previous 2m cable..this causes a buzz as soon as i plug it in to the speaker (i don't have to touch the other end)....
Q2) so why does a 4m cable cause a buzz but a 2m cable doesn't??

thanks

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Jeff
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Answered (Verified) Jeff replied on Mon, Nov 11 2013 3:43 PM
Verified by moshejay

That's your problem right there. Never, ever connect a line in device to a speaker level out without an appropriate convertor,mand even then it's an awful idea as you get more distortion. The amo obviously lifts ground when off on the amps, or the hum is there but as you say hidden ipunder the signal. 

If you go too high on the volume you can fry the inputs of the speaker, they are designed for low voltage and current input, speaker level can push much higher voltages and current. 

B&O used to sell an adaptor to convert line speaker level down to line level, no idea if they still do or not. Steve at Sounds Heavenly might be able to cook up such adapters if you really must go that route, he's a pleasure to deal with. 

Jeff

I'm afraid I'm recovering from the BeoVirus. Sad

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Jeff
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Jeff replied on Mon, Nov 11 2013 2:43 AM

An unterminated cable acts like an antenna for the various types of electromagnetic noise out there, primarily from the power mains (50 or 60 hz depending on country). Touching the end adds your body to the mix, you can act like a great antenna due to all the water in the body. A longer cable can be more susceptible to noise pickup especially depending on how the two are mated, if the connection is loose particularly. More cable length means a longer antenna and more gain.

This is not unusual at all, in fact I've experienced the same with my Lab 8000's when hooking them up via RCA cable to an iPod dock. That's why I usually unplug the speakers until I complete all connections, sometimes the hum/buzz can be loud enough to potentially damage the speakers.

Jeff

I'm afraid I'm recovering from the BeoVirus. Sad

moshejay
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Suggested by stampfki

Thanks Jeff...you put it quite well!

To go a little further with this...

i now attach the free end of the RCA cable to a speaker outlet on a surround amp that has been switched OFF.
Buzzing REMAINS.

I then switch the amp ON and the buzzing disappears (to be truthful i'm not sure if it disappears immediately or only once the volume reaches a certain minimum level, but the point is it disappears once the amp is powered up).

So new question....what is the amp doing that stops the buzzing?
another new question...can anything be done to prevent the buzzing whilst the amp is switched OFF? (eg a resistor between -ve terminal of the amp's speaker connection and its ground plane assuming i can find it)

thanks again

Jeff
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Jeff replied on Mon, Nov 11 2013 7:34 AM

What do you mean by amps speaker outputs? Do you mean an RCA plug out that's at line level, or the two conductor speaker outputs that are amplified? If the former, it sounds like there is some fault where the amp is letting ground float when it's switched off. I'd try another preamp or such and see if the same problem occurs.

If it's really speaker outs, that shouldn't be used to connect to any line level input, not without a drop down resistor and even then that usually doesn't work well.

It does this regardless of cable, and on both speakers?

Jeff

I'm afraid I'm recovering from the BeoVirus. Sad

moshejay
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moshejay replied on Mon, Nov 11 2013 10:24 AM

i really do mean the 2 conductor speaker outputs that one would connect a std speaker to. And yes, i do realise they are amplified and that did concern me.
However, the manual for the 6000 does not specifically mention that one can not draw the signal for the 6000 from the amp speaker outputs so i assumed one could. And, looking at the circuit diagram i see the RCA circuit bypasses the amp circuit on the 6000 so i assumed it would be OK.

are my assumptions all wrong??

And yes, this happens regardless of the RCA cable connected.

And I have yet to try a lineout connection.

Jeff
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Answered (Verified) Jeff replied on Mon, Nov 11 2013 3:43 PM
Verified by moshejay

That's your problem right there. Never, ever connect a line in device to a speaker level out without an appropriate convertor,mand even then it's an awful idea as you get more distortion. The amo obviously lifts ground when off on the amps, or the hum is there but as you say hidden ipunder the signal. 

If you go too high on the volume you can fry the inputs of the speaker, they are designed for low voltage and current input, speaker level can push much higher voltages and current. 

B&O used to sell an adaptor to convert line speaker level down to line level, no idea if they still do or not. Steve at Sounds Heavenly might be able to cook up such adapters if you really must go that route, he's a pleasure to deal with. 

Jeff

I'm afraid I'm recovering from the BeoVirus. Sad

wonderfulelectric
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Well this same thing happened to mine too. I think it has got to do with grounding issues. Being that your body carries current in some way?

moshejay
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thanks Jeff...

going to see whether this amp has line level outputs that i can use...i rather suspect that if it has, then it expects the connecting device to have a volume control!!

 

moshejay
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thanks for your confirmation wonderfulelectric

Steve at Sounds Heavenly
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Hi Jeff,

Thanks for your kind words, you are too kind! Laughing

I hope that you managed to resolve the issues moshejay and wonderfulelectric, but I'm always happy to help if you do have any noise problems that still need to be resolved (sorry I didn't see the forum thread sooner).

Kind regards, Steve.

Steve.

www.soundsheavenly.com

Founder of Sounds Heavenly Cables and Brand Ambassador for Bang & Olufsen

Sounds Heavenly are proud to sponsor BeoWorld!

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