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Shielding components from EMI/RFI... Help please

A recent experiment with a product designed to reduce EMI/RFI left me curious about other ways to reduce EMI/RFI in my system. In the past ten days, I've stepped onto a slippery slope, at the bottom of which is surely some kind of insanity...

I've been experimenting with copper plates in an effort to absorb, deflect, diffract, and block EMI/RFI. I've tried copper plates under components, on top of components, and inside components.

This is the point where you tell me I don't know what I'm doing and I'm likely to short circuit something and/or electrocute myself. Consider me duly warned. This is also the point where you tell me to get some balanced interconnects, or at least to get some shielded interconnects for Chrissake. Consider me duly informed. Moving on...

I'm hoping you can help me make the most of this experiment, and help me avoid killing a component or myself. My strategy so far has been to:

1. Place copper plates at locations that generate a lot of EMI/RFI, e.g., components with switching mode power supplies or high frequency clocks. The system has a total of 3 SMPS and 3 clocks.

2. Place copper plates at locations that are vulnerable to EMI/RFI, e.g., under the amp, near the transformer.

3. Place copper plates inside noisy components -- in particular, my Meridian G68 preamp/processor. I've begun to build 2 partial Faraday cages, one for the SMPS, and one for the analog output stage.

4. Ground the copper plates either to the component chassis (when plates are used inside a component) or to an independent ground point (when plates are used above/below a component).

Has anyone tried this sort of thing?

Bryon
bryoncunningham
bryoncunningham OP
893 posts
 
Sean - I think my results, if they can be generalized, point to the value of extensive shielding in dac's and cd players, all of which have clocks, and many of which have noisy power supplies. I agree that it's strange that you don't see extensive shielding more often. The copper for the shielding in my G68 cost me about $100. That's a very small fraction of the current $12K msrp.

Jim - The ground rod wasn't based on magical thinking. It was based on the belief that the ground for a Faraday cage should be different from the ground for the equipment inside the cage. I gather from your comments that that is incorrect.

When I installed the copper shielding inside the G68, I grounded it to the G68's chassis. The dedicated ground rod was used only for the 2 enclosures - one for the reclocker and one for the Sonos. I have disconnected the ground rod and connected the enclosures' ground cables to a conductive spot on the G68's chassis. My initial impression is that I can hear no difference between that arrangement and my previous one.

Bryon
bryoncunningham OP
893 posts
 
After more extensive listening, I've concluded that grounding the new enclosures to the Meridian G68 resulted in sound that is slightly worse, particularly in "listening ease" at loud volumes. Here are the 3 arrangements I've tried:

1. Enclosures grounded to ground rod.
2. Enclosures not grounded.
3. Enclosures grounded to G68.

I can say with some degree of confidence that (1) and (2) sound better than (3), but I cannot say with much confidence whether (1) sounded different from (2). So maybe the ground rod is adding nothing other than additional risk.

As for why (3) sounded worse than (1) and (2), I don't know what to say. Maybe grounding the enclosures to the G68 made the enclosures act like antennas collecting RFI, and that RFI was then transmitted into the G68? I don't know. I'm out of my depth. Maybe someone has a theory.

bc
almarg's avatar
almarg
9,670 posts
 
Hi Bryon,
As for why (3) sounded worse than (1) and (2) ... maybe grounding the enclosures to the G68 made the enclosures act like antennas collecting RFI, and that RFI was then transmitted into the G68?
That would certainly seem like a possibility. In particular, perhaps noise originating from the enclosed devices is finding its way from the connection to the G68 chassis to the ground/signal return of the digital input to the G68. A noisy ground at that circuit point would certainly contribute to jitter, especially if the connection is unbalanced S/PDIF rather than balanced AES/EBU.

Question for Jim:

Although the additional ground rod may very well not be helpful with respect to minimizing noise, I'm wondering how it would represent a safety risk in this particular application.

There are two reasons I can think of why code prohibits multiple ground rods that are not connected together.

One is that if it is used to ground the safety ground of an electrically powered device, fault current may not cause the circuit breaker to trip. That is explained on page 8 of this Bill Whitlock paper.

The other reason I can envision, which is also mentioned in the paper, is that if lightning hits the outdoor electrical wires and is conducted to ground through the main grounding rod, thousands of volts may briefly appear between the two grounding rods, potentially damaging anything for which a connection path to both of them exists.

Neither of those scenarios seems applicable to what Bryon was doing with the second ground rod, assuming that the means of insulation between the Reclocker and the Sonos and their grounded enclosures is sufficient to withstand the voltage that would appear across it during the lightning strike scenario. Perhaps that isn't a good assumption, though. Can you explain further? Thanks.

Best regards,
-- Al
jea48
4,689 posts
 
Neither of those scenarios seems applicable to what Bryon was doing with the second ground rod, assuming that the means of insulation between the Reclocker and the Sonos and their grounded enclosures is sufficient to withstand the voltage that would appear across it during the lightning strike scenario.

Al,

You hit the nail on the head. The insulation would possibly have to withstand hundreds of thousands of volts. Though quicker than the blink of an eye, still long enough to damage solid state devices.
Odds? No idea.... But if the connection to the rod made no difference in sound why take the chance.

If memory serves me right a lightning strike can travel through the earth for 5 miles.
>>>

I can say with some degree of confidence that (1) and (2) sound better than (3), but I cannot say with much confidence whether (1) sounded different from (2). So maybe the ground rod is adding nothing other than additional risk.
02-13-12: Bryoncunningham
A Faraday cage does not have to be earth grounded to work.

Though usually, say in the case of a 2 wire cord and plug piece of electronic equipment such as a CDP, the Faraday cage (metal enclosure) is connected to the signal ground.

Electronics RFI shielding/Faraday cages of a Stealth Bomber are not connected to the earth.
almarg's avatar
almarg
9,670 posts
 
Thanks Jim!

Best regards,
-- Al
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