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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
 
That is good advice, Sarcher. I had a similar journey with analog interconnects. After trying a number of different shielded interconnects from well respected manufacturers, I settled on an unshielded pair. As you describe, the sound was more open and airy with the unshielded cables. I've also experimented with shielded and unshielded power cables, and found that I preferred them unshielded or minimally shielded.

I guess I'm learning that I have a different attitude about shielding analog signals and power cables vs. shielding digital signals and digital circuits. The digital interconnect I settled on is double shielded. Very happy with it. As I mentioned in the OP, I have 3 digital devices with high speed clocks and switching mode power supplies. I've built complete shields for 2 of the digital devices, and a partial shield for the other. I recently removed the shields to make some other changes and I discovered that I definitely prefer the sound with digital devices shielded rather than unshielded. It wasn't so much a matter of audible noise as it was a matter of high frequency grain and glare. I guess that I could sum up my (admittedly limited) experience by saying that...

Shielding analog cables and power cables tends to reduce openness and air :-( whereas shielding digital cables and digital circuits tends to reduce grain and glare :-)

I have no idea if that is generalizable.

bc
sarcher30
596 posts
 
That is an interesting observation about digital interconnects. I have a Linn DS which uses an ethernet connection from a NAS in a different room. I wonder if your theory would apply in my situation? I'm not sure if ethernet cables benefit from more shielding? Guess I could search the net to see what pops up.
bryoncunningham OP
890 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
9,670 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
890 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?
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