Shielding Characteristics of Copper Clad PCB - diyAudio
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Old 29th January 2012, 09:29 PM   #1
John L is offline John L  United States
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Default Shielding Characteristics of Copper Clad PCB

If I wish to finish off some 'plain Jane' amplifier transformers, by making custom transformer covers, and I were to use copper clad PCB, how much shielding effect would it have for the rest of the amplifier?

And would there be a difference between single sided and double sided clad boards?

Here is where I got the idea. Originally I had thought that using 1/14" to 1/2" wood, to put together the project would be a great start. Then custom cut some thin sheet metal for the inside top, and the four inner sides, followed by soldering.

I figured that it would act as a nice shielding. But after seeing this project above, I think it may be the best way to go. And as an added bonus, the copper finish would really add to the looks of the amplifier if arranged properly. Also the rounded edges could be hand painted with matching paint, sanded smooth, and form a perfect finish all around.

So, are the shielding qualities good?
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Old 29th January 2012, 09:39 PM   #2
jcx is online now jcx  United States
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with transformers we usually worry about magnetic field leakage - for power line frequencies thru audio Cu foil does little - except for a "belly band" shorted trun around the whole xfmr - and even that has limited effect

a low carbon steel box (perf metal for ventalation) is the most practical performance/cost way of shielding trasformers


toroids have little magenetic field leakage compared to EI
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Old 29th January 2012, 09:49 PM   #3
John L is offline John L  United States
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Quote:
Originally Posted by jcx View Post
with transformers we usually worry about magnetic field leakage - for power line frequencies thru audio Cu foil does little - except for a "belly band" shorted trun around the whole xfmr - and even that has limited effect

a low carbon steel box (perf metal for ventalation) is the most practical performance/cost way of shielding trasformers


toroids have little magenetic field leakage compared to EI
Yes, but they have the distinction of being ugly, unless painted or laminated by hand.

But my question still remains: even though there is better, how good would the copper clad PCB case be, especially if double sided?
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Old 29th January 2012, 10:15 PM   #4
jcx is online now jcx  United States
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Ness Engineering Tech Data - Skin Depth and Skin Effect

gives 1/2" for 6061 @60 Hz - and one skin depth is only ~40% attenuation

you can put in Cu, typical pcb foil thickness


steel can be plated, Chrome plating custom shops for auto, bike parts are everywhere
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Old 29th January 2012, 10:49 PM   #5
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Copper clad PCB is an excellent shield at radio frequencies, for radio waves, but it doesn't help much with 50 or 60 Hz hum induced by magnetic fields. It's not a magnetic material.

The good news is that standalone transformer boxes give you access to 2 of the principal and cheapest methods of minimizing hum pickup, distance and orientation. Turn them around until hum is at a minimum. Move them further away until the amplitude reaches an acceptable level.

Got the picture?

PCB is a low-cost, low-effort and attractive material for enclosure fabrication, just don't depend on it to shield magnetic flux leakage.
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Old 29th January 2012, 10:55 PM   #6
John L is offline John L  United States
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Quote:
Originally Posted by counter culture View Post
Copper clad PCB is an excellent shield at radio frequencies, for radio waves, but it doesn't help much with 50 or 60 Hz hum induced by magnetic fields. It's not a magnetic material.

The good news is that standalone transformer boxes give you access to 2 of the principal and cheapest methods of minimizing hum pickup, distance and orientation. Turn them around until hum is at a minimum. Move them further away until the amplitude reaches an acceptable level.

Got the picture?

PCB is a low-cost, low-effort and attractive material for enclosure fabrication, just don't depend on it to shield magnetic flux leakage.
Thank you much.
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Old 30th January 2012, 12:03 AM   #7
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This link may help you:
http://www.analog.com/static/importe...7248AN_347.pdf
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