Guest Yevgenip Posted January 12, 2005 Report Share Posted January 12, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2005 Report Share Posted January 12, 2005 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". Quote Link to comment Share on other sites More sharing options...
ante Posted January 12, 2005 Report Share Posted January 12, 2005 Hi Guys,If the monitor can do this to the speakers, what can it do to you! :o If the monitor is new and the power core is properly grounded this can Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 12, 2005 Report Share Posted January 12, 2005 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. :oMaybe Yevgeni's computer speakers have an unshielded audio input transformer that is picking it up. ??? Quote Link to comment Share on other sites More sharing options...
trigger Posted January 13, 2005 Report Share Posted January 13, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 13, 2005 Report Share Posted January 13, 2005 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". Quote Link to comment Share on other sites More sharing options...
ante Posted January 13, 2005 Report Share Posted January 13, 2005 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 Quote Link to comment Share on other sites More sharing options...
trigger Posted January 13, 2005 Report Share Posted January 13, 2005 haha...... ;DI 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......... :P Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 13, 2005 Report Share Posted January 13, 2005 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". Quote Link to comment Share on other sites More sharing options...
ante Posted January 13, 2005 Report Share Posted January 13, 2005 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: Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 13, 2005 Report Share Posted January 13, 2005 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. ::) Quote Link to comment Share on other sites More sharing options...
trigger Posted January 14, 2005 Report Share Posted January 14, 2005 ok, I will open my monitor and take some photo..... before I throw it away.......... even it is still working......... :-X Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 14, 2005 Report Share Posted January 14, 2005 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? Quote Link to comment Share on other sites More sharing options...
ante Posted January 14, 2005 Report Share Posted January 14, 2005 This black plastic is supposed to take care of some of the radiation. I don Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 14, 2005 Report Share Posted January 14, 2005 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. Quote Link to comment Share on other sites More sharing options...
ante Posted January 15, 2005 Report Share Posted January 15, 2005 Hi Audioguru,The cage isn Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted January 16, 2005 Report Share Posted January 16, 2005 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. Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 16, 2005 Report Share Posted January 16, 2005 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 Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted January 17, 2005 Report Share Posted January 17, 2005 So that's it? Well, I guess I can't really do anything about it then.Well, no matter - Thanks anyway! ;D Quote Link to comment Share on other sites More sharing options...
audioguru Posted January 17, 2005 Report Share Posted January 17, 2005 the speakers do not have a shielded input.Hi Yevgeni,Of course you can eliminate the hum. Just use shielded audio cable to connect the computer to the input of the amplified speakers.All audio amplifier systems use shielded cables to eliminate hum and other interference. ;D Quote Link to comment Share on other sites More sharing options...
Guest Yevgenip Posted January 19, 2005 Report Share Posted January 19, 2005 O.k. I'll try that, thanks! :) Quote Link to comment Share on other sites More sharing options...
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