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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
888 posts
 
I also use ethernet. My understanding is that most (all?) ethernet protocols employ a variety of error detection/correction techniques that ensure perfect or near perfect data transmission.

If that is true, then I would imagine that additional shielding on ethernet cables would have little or no effect. But what do I know? Maybe it would have some effect. Stranger things have happened in the world of audio.

Maybe someone who knows this stuff better will weigh in.
almarg's avatar
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almarg
8,673 posts
 
Bryon & Sarcher30, IMO shielding an ethernet cable will provide no benefit with respect to the integrity of the data it is carrying, or with respect to the amount of jitter that will result when that data is ultimately converted to analog (since the data is buffered at the receiving end). However, I would not completely rule out the possibility that shielding the cable could be helpful in terms of minimizing the amount of digital noise that could couple FROM the cable to arbitrary circuit points within the system.

From this paper by Steve Nugent:
Networked audio (Ethernet), both wired and WiFi is a unique case. Because the data is transmitted in packets with flow-control, re-try for errors and buffering at the end-point device, it is not as much of a real-time transfer as USB, S/PDIF or Firewire. The computer transmitting the data packets must still keep-up" the pace to prevent dropouts from occurring, but the real-time nature of the transfer is looser. Unlike with other protocols, there can be dead-times when no data is being transferred. Networking also avoids the use of the audio stack of the computer audio system since it treats all data essentially the same. This avoids kmixer on XP systems and the audio stacks on Mac and PC Vista. Because of the packet-transfer protocol of Ethernet and data buffering at the end-point, the jitter of the clock in the computer is a non-issue. The only clock that is important is the one in the end-point device. Examples of end-point devices are: Squeezebox, Duet and Sonos. This would seem to be the ideal situation, which it certainly is. The only problem that can occur is overloading the network with traffic or WiFi interference, which may cause occasional dropouts. The problem for audiophiles is that the majority of these end-point devices were designed with high-volume manufacturing and low-cost as requirements, with performance taking a lower priority. As a result, the jitter from these devices is higher than it could be. It should be the lowest of all the audio source devices available.

Best regards,
-- Al
bryoncunningham OP
888 posts
 
Thanks, Al. That's what I suspected, but it's good to hear from someone who actually knows something (in this case, both you and Steve).

On the issue of ethernet cables themselves releasing EMI/RFI... I have no idea whether my ethernet cables are shielded. Is there a way to determine that without cutting into them?
sarcher30
596 posts
 
Almarg, that makes sense. Thanks for the info.

Bc, I found some sheilded cat6 cable online. It was cheap enough I decided to give it a shot anyway. I have to run my ethernet fairly close to some power cords because my house is not prewired with it. I'm using some cat5 I made myself now. I know it is not sheilded. I think if your ethernet cable is sheilded it will say so on the jacket.

Sean
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almarg
8,673 posts
 
Also, in many cases either the letters UTP (unshielded twisted pair) or STP (shielded twisted pair) will appear on the cable.

Or if a manufacturer's part number appears on the cable, Googling that number will presumably lead you to a description of the particular cable, and whether or not it is shielded.

I believe that it is considerably more common for CAT 5e cable to be unshielded than shielded. Not sure about CAT 6.

Another point to keep in mind, I believe, is that the shield in most or all shielded ethernet cables will only be grounded if the jack it is plugged into makes that provision, and I believe that only shielded jacks will do so.

Best regards,
-- Al
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