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Old 25th June 2002, 03:20 PM   #1
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Default Magnetic Interactions

Hello All, I thought I should relate a recent observation.
My PC workstation is a corner table with monitor on the table-top, and a vertical rack with amplifier, 14" TV/monitor and Vcr mounted, and Boston Acoustics A40 6-1/2" 2 ways on either side.

The amplifier that I am currently using (I have plenty of choice in amps) is a classic 1964 Panasonic Am/Fm all tube reciever.
This on a thin steel shelf 3" above my PC monitor.

My observation is that the PC display is modulated (jumps around) by the stray power AND audio fields, and in sympathy with the audio, and according to audio level.

It seems that these stray fields are quite strong, and not to be disregarded when building tube amps.
Maybe this is a help for some.

Regards, Eric.
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Old 25th June 2002, 03:36 PM   #2
PassFan is offline PassFan  United States
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Thanks for the warning. My amp is in close proximity to my CPU though seperated by about 1 foot and a couple inches of wood. I have about 2 feet to the monitor. I havn't had any problems so far but I will bear this in mind for any future changes. One other thing though, my chassis are made out of solid oak and not metal boxes. Perhaps shielding has something to do with expanding the field. Something to think about. Thanks again.
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Old 26th June 2002, 05:56 PM   #3
dhaen is offline dhaen  Europe
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Default Really?


Are you sure it's not acoustical/mechanical?
What I mean is that if you vibrate a scanned device (CRT monitor), it interferes with the visual perception of the scan.
If you don't believe me, try this trick:
Clean your teeth with an electric toothbrush while in front of your CRT monitor.
The display seems to jump about like mad!
Of course this trick is actually the reverse of my suggestion, (by vibrating the observer) but it illustrates my point.
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Old 26th June 2002, 06:22 PM   #4
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Hi dhaen
It is definately magnetic coupling.
The display jitter is a bit like when degaussing, except with audio component, and level and distance related.
I was just bringing to attention the levels of the radiated magnetic fields.

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Old 26th June 2002, 07:05 PM   #5
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The electron beam is very sensitive to stray magnetic fields of any kind, even that of earth, which is much smaller than the local fields created by the OPTs of a power amp. And yet degaussing is to remove the influence of the earths magnetic field.

My 2 cents.

Gabe CGV Electronics
Home of the CGV-300B amplifier on a budget
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Old 26th June 2002, 09:24 PM   #6
dhaen is offline dhaen  Europe
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Ok Eric, I conceed.

I was just a little surprised at the level from the distance you described. But now that you detail the purity/ landing distortion as well as the registration error, you must be right.
I've spent more than a little time with CRT's, and during my stay (15 years or so), we spent a lot of effort reducing this effect.

Thanks for the alert.
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