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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
890 posts
 
Thank you, Al, for your help. In light of Jim's advice, I've abandoned the idea of using a dedicated ground rod. Even though I live in Southern California where lightning is rare, there's no good reason to take the risk. It's really no sacrifice anyway, because I could not hear a difference between the enclosures grounded vs. ungrounded.

The improvement from adding the two additional enclosures (whether grounded or ungrounded) was perceptible but not dramatic. The big improvement came from adding shielding INSIDE the G68 (grounded to the chassis). With that in mind...

I've been reading that copper is effective at shielding high frequency RFI, but not particularly effective at shielding low frequency EMI. So I'm thinking about adding a layer of STEEL shields around the G68's power supply, bolted directly to the copper plates that are already in place.

bc
magfan
1,583 posts
 
Try this:

http://en.wikipedia.org/wiki/Mu-metal
bryoncunningham OP
890 posts
 
Question...

Looking inside the Meridian G68, I see that the power is grounded to the chassis at TWO points. A ground wire connects the IEC input to the chassis. A second ground wire connects the power supply to the chassis.

The unit has been modified extensively, both by me and by a professional modder, so I don't know how it was grounded when it came from the factory.

Is it okay for the power to be grounded to the chassis at two points? Or am I creating a ground loop?

Thanks,
Bryon
almarg's avatar
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almarg
9,670 posts
 
Hi Bryon,

My suspicion would be that the connection from the power supply is connecting the ground on the DC output side of the supply to chassis, thereby connecting the G68's circuit ground to chassis. That is often done, although as you surmise it can result in a ground loop between the G68 and the components it is connected to.

I wouldn't play around with it, though, unless there is a particular reason to do so, and an understanding of why it was done that way. Other possible approaches, btw, besides simply removing the connection, being to connect circuit ground to chassis via either a resistor, a capacitor, or an inductor.

Keep in mind, also, that balanced connections have much less susceptibility to ground loop issues than unbalanced connections. I assume that you have a balanced connection to the Pass amp, and perhaps also a balanced AES/EBU connection from the re-clocker.

Best,

-- Al
bryoncunningham OP
890 posts
 
My suspicion would be that the connection from the power supply is connecting the ground on the DC output side of the supply to chassis...

You may be right, Al, although the ground wire on the power supply is right next to the power INPUT. Here are some pics...

Modded PSU photo 1

Modded PSU photo 2

Modded PSU photo 3

Stock PSU

The power input is the blue/red wires in the top left of photo 1. The ground is the green wire in the bottom left of photo 1.

Can you tell from looking at those pictures whether the ground is on the AC side or the DC side? Can we infer from its physical location that it is on the AC side?
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