Speaker buzzing

[Yevgenip]

Hi.
My PC Speakers (not built in) buzz strongly when I turn on the power supply to them, even if they are not on. I figured that that buzzing is the result of a strong electromagnetic field which is created by the transformer. I guess the smart people who built the speakers put the switch on the transformer's output insted of the input.
Will changing the switch's connection to the transformer's input solve it? And why is it buzzing?

Thanks.

 

[audioguru2]

Hi Yevgeni,
I think that the buzz is caused by the strong magnetic field that moves your CRT monitor's beam vertically. Try moving the speakers and their input cable a meter away from the monitor to see (hear?) the buzz go away.
Don't the speakers have a shielded input cable?

Pickup of noise from the power supply transformer would cause a smooth "hum" not a "buzz".

 

[ante1]

Hi Guys,

If the monitor can do this to the speakers, what can it do to you! If the monitor is new and the power core is properly grounded this can

 

[audioguru2]

Hi Ante,
Don't worry about the monitor. The deflection yokes of most CRT's are not magnetically shielded and the magnetic sawtooth radiation can be picked-up by other electronic items. It could be heard in my telephone's earphone even when it was unplugged.
Maybe Yevgeni's computer speakers have an unshielded audio input transformer that is picking it up. ???

 

[trigger]

As Ante said, nowadays monitors are properly shielded. It is hard to beleive the "buzz" is from the monitor.

May be the jack of the speaker has been oxidized , try to clean it up.

 

[audioguru2]

Hi Trigger,
Ante is referring to the high voltage section of a monitor which is shielded to prevent any sparks from causing radio interference. I am referring to the "deflection yoke", which are coils mounted on the neck of the CRT to electro-magnetically move the beam. I have never seen those coils with a shield.
It is difficult and expensive to magnetically shield something. Iron or steel doesn't shield very well and mu-metal is expensive. The monitor's vertical deflection magnetic pulses at 50Hz, 60Hz or 75Hz would certainly be heard as a "buzz".

 

[ante1]

No, not only the high voltage parts but also everything else inside is shielded in new monitors. All this shielding has no effect if the power core isn

 

[trigger]

haha...... ;D

I have opened my poor monitor some months ago... since it got some strange color....... oh....... it is some loose connection between the PCB sockets and the cathode ray tube pins ........

I found that PCB, with high frequency components are all covered with a metal bracket........ so ........ if it is not a shielding then.... I will got a big buzz at my desktop amp.........

 

[audioguru2]

Hi Guys,
Here is a pic of a computer monitor's or TV's CRT.
The end on the left has the brightness amps mounted on a PCB that plugs into the pins of the CRT. That PCB is usually shielded because it has several pins with fairly high voltages on them for focus and screen grids. The brightness amps operate at high frequencies that may cause radio interference if not shielded.
In the middle of the CRT's neck are the large and powerful deflection coils. I have never seen them magnetically shielded nor with a core. Their electro-magnetic pulses radiate nearly 1 metre. An audio amp's unshielded input cable or input transformer would act like an antenna and pickup the pulses as a "buzz".

View attachment 36459

 

[ante1]

Here you can see an old monitor inside which have only partially shielded coils on its neck. http://www.electronics-lab.com/action/gallery/inside_crt/ In the newer ones it looks more like this:

View attachment 36461

 

[audioguru2]

Hi Ante,
I don't see a shield over the deflection coils, do you? ???
I just see some kind of plastic structure that holds the coils. :

 

[trigger]

ok, I will open my monitor and take some photo..... before I throw it away.......... even it is still working......... :-X

 

[audioguru2]

Never mind, Trigger.
Your monitor is not causing the buzz. We need to see if Yevgeni's monitor's deflection coils aren't magnetically shielded and therefore is causing his buzz.

Yevgeni,
Do the speakers still buzz when they are located at least a metre away from your monitor?
Do the amplifiers/speakers have shielded input cables that are not near the monitor?
The speakers make a rough buzz, not a smooth hum, don't they?
When you unplug the speakers' input cable from the computer, does the buzz go away?

 

[ante1]

This black plastic is supposed to take care of some of the radiation. I don

 

[audioguru2]

Hi Ante,
I covered the entire neck of the CRT in my 'scope with mu-metal to stop nearby transformer and flourescent light ballast interference that showed on its screen. My 'scope is fully enclosed in a grounded steel case and the electro-magnetic interference went right through it! The mu-metal works very well and it isn't even connected to anything.
Maybe monitors have a shield to stop external interference from showing on their screen.

 

[ante1]

Hi Audioguru,

The cage isn

 

[Yevgenip]

Well, The speakers actually hum, not buzz. It is definetly the speakers and not the monitor. the speakers do not have a shielded input.

Thanks.

 

[audioguru2]

Hi Yevgeni,
Goodbye buzz, hello hum!
A speaker amplifier's input cable without a shield makes a nice receiving antenna for mains hum, doesn't it? ;D

 

[Yevgenip]

So that's it? Well, I guess I can't really do anything about it then.
Well, no matter - Thanks anyway! ;D