@bryoncunningham You have a very nice clean rack of equipment. Many of us are trying to reach nirvana with our audio systems. I applaud your endeavor of re-engineering some of your components to resist EMI/RFI. Many would not bother with this. What has motivated you to re-engineer your components? Were you actually experiencing noises and higher than average noise floors? Does your system incorporate any balanced devices, or is it all unbalanced RCA?
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
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
115 responses Add your response
Hi guys, if you need any advice regarding EMI or RFI shields, maybe to check with this guys: http://masach.partcommunity.com/ As much as I can see, they have 3D models and quite wide range of shields. Hope it can help. |
On a whole, though, lots of recommendations to apply shielding solutions to digital equipment. Is this because they are sensitive to EMI or because they are big EMI emitters?Mainly because they are big EMI emitters. A notable exception to that perhaps being circuit points that are involved in the timing of D/A conversion. Pickup of radiated noise at those points could conceivably have audible significance as a result of its effects on jitter. Regards, -- Al |
01-30-13: CambIME, the biggest gains in SQ were made by shielding the G68 from ITSELF. In other words, shielding the analog board from the digital boards and shielding the power supply from both the analog and digital boards. Bryon |
Another update from my crusade against EMI/RFI... A couple years ago, I relocated all my equipment to a closet, which you can see here. To reduce heat buildup, I installed a large fan in the ceiling of the closet. Today, I finally got around to DIY'ing an EMI/RFI fan filter, which you can see here. It's made from steel and copper mesh, and it covers the entire ceiling of the closet. Obviously, I don't have much of a life. But that's not the point. The point is: it works. Definitely an improvement in SQ. I was surprised. Again. Bryon |
Yes, Onemug, I did notice a small improvement after they had about 100 hours on them. I am very impressed with the performance of the AC-9's. Remarkable for the price. The fact that I preferred the very affordable AC-9's to the very expensive Pythons illustrates a point Al has made many times... in the world of cables, the correlation between price and performance isn't that strong. Bryon |
Bryon, Did the Pangea AC-9s change much after "x" amount of time? Reason I ask is that I bought a few of them a year ago. I can't say anything bad about them but I found some cords I liked better. I just kept them because I'm too lazy to sell them. Now I need a cord and may give these a second chance. I didn't put many hours on them after I got them. I admire your honesty in saying you liked them better than the more expensive ones. |
Update for anyone still interested in my adventures in EMI/RFI reduction... Three more changes: --I replaced the unshielded power cords for the power conditioner, the preamp, and the amp with shielded power cords. An improvement, even though I went from three $1100 cords (Shunyata Pythons) to three $100 cords (Pangea AC-9's). --I added copper "sleeves" to the ends of all power cords in the system, as described here. --I wrapped the external hard drive where my music is stored with TI Shield. All three were improvements, but the biggest and most surprising improvement was wrapping the external drive with TI Shield. Don't know what to make of that. FWIW. Bryon |
Hi Dave - Thanks for those links. They are very informative. As far as A'gon rejecting your post because it was "too short," that is just strange. And arbitrary. My last post on this thread was two words long. What's more, it seems like I've been hearing more and more A'gon stories of people whose posts are being rejected for one reason or another. Maybe there is new management in Moderatorland. While I certainly understand the need to moderate forums for content that is truly objectionable, one of the things I always liked about A'gon is that it erred on the side of permissiveness rather than censorship. Not long ago, I joined another audiophile site, where 3 out of my first 15 posts were edited by a moderator. It was creepy. I stopped posting there altogether. Whether it's in the virtual world or the real world, the excessive control of speech has a chilling effect on the exchange and progression of ideas. Let's hope this trend doesn't continue. Bryon |
Funny story ... a few weeks back I attempted to leave you this link FERRITES on Ferrites ... thought it might be helpful at that time and I knew you would be very interested The post was very short something like ... Check [this] out ... After a day or so .. my post never appeared in your thread ... and I couldnt figure out what was so derogatory or in conflict ??? Shortly after that I received a email from A/gon a day or so later saying ... Thank you for your submission but we are afraid we can post it as it is .. To Short .. and would take up valuable space in the archives ... please lengthen your post and resubmit So this is my attempt at lengthening the post and getting you the info I know you will appreciate Heres another link at chasing RF sources in your house RF interference HTH Dave |
Hi Bryon, It can't hurt to put a ferrite on DC, and it conceivably could provide some benefit. The ferrite will have no effect on the DC itself, but would provide some amount of attenuation of RF noise that might be riding on it, the RF perhaps being generated within the wall wart itself if it is the non-linear (switching) type. Best regards, -- Al |
Thanks, Al. That looks like a great reference guide, though much of it is over my head. I think at some point I'll take a course in electronic engineering, to get a firmer grasp on some of the more difficult concepts. I read a few of Ott's articles and tech tips on his website. I particularly enjoyed this one. bc |
Is the dissipation potential of a chassis determined by its surface area, its mass, its material, its conductivity, its magnetism...? Several of the above?Excellent question, but I have no particular knowledge of what the answer might be. I suspect, however, that the answer will be a combination of those factors, and that the optimal combination will vary as a function of the frequency components of the noise. And unfortunately digitally-induced noise will typically have spectral components covering a huge range of frequencies. If you are feeling particularly ambitious at some point, I suspect that some good answers can be found in "Electromagnetic Compatibility Engineering", by the distinguished expert Henry W. Ott. Best, -- Al |
I agree that the current configuration seems to maximize the benefit of the reclocker's galvanic isolation. I have a follow up question for you, Al, about the dissipation of noise in an equipment's chassis... Is the dissipation potential of a chassis determined by its surface area, its mass, its material, its conductivity, its magnetism...? Several of the above? bc |
The plate is directly under the switch. I placed it there to keep the braided ground strap as short as possible, to minimize any antenna effect. Out of curiosity, is there another reason why it should be directly under the switch?Just my vague intuitive feeling that placing it there might enhance the effectiveness of the switch's internal ground plane, perhaps reducing the amount of digital noise generated within the switch that might end up coupling or radiating to points downstream. With regard to the well thought out summary you presented in your last post, my only comment is that it would seem to make sense that the best results were obtained via a configuration that does not provide any paths that bypass the reclocker and its galvanic isolation. As you noted, such a path previously existed, via the ground wire from the switch to the conditioner, and from there via power cords to the downstream components. Well done! Best, -- Al |
Yes, Al, the plate is directly under the switch. I placed it there to keep the braided ground strap as short as possible, to minimize any antenna effect. Out of curiosity, is there another reason why it should be directly under the switch? Also, I neglected to mention that I also changed another variable: I replaced the 1' unshielded ethernet cable between the switch and the Sonos with a SHIELDED version. So prior to this change, the configuration was... computer -> 50' shielded Cat6 cable -> ethernet switch (grounded to power conditioner/earth) -> 1' unshielded Cat6 cable -> Sonos -> reclocker... And my continuity results were... Ethernet switch to Sonos input NO continuity Ethernet switch to Sonos output NO continuity Ethernet switch to reclocker input NO continuity Ethernet switch to reclocker output continuous Ethernet switch to Meridian G68 continuous Ethernet switch to Pass amp continuous So the break in continuity was due to (a) the galvanic isolation in the reclocker and (b) the UNSHIELDED ethernet cable between the switch and the Sonos. Now the configuration is... computer -> 50' shielded Cat6 cable -> ethernet switch (not grounded to power conditioner/earth, but grounded to the "grounding plate") -> 1' SHIELDED Cat6 cable -> Sonos -> reclocker... And the continuity results are the "OPPOSITE"... Ethernet switch to Sonos input continuous Ethernet switch to Sonos output continuous Ethernet switch to reclocker input continuous Ethernet switch to reclocker output NO continuity Ethernet switch to Meridian G68 NO continuity Ethernet switch to Pass amp NO continuity So now the upstream half of the system (computer, ethernet switch, Sonos, reclocker input) is discontinuous from the downstream half (reclocker output, preamp, amp). In this new arrangement, the high frequencies are improved, which is consistent with my listening results from 3/3, where the presence of a SHIELDED ethernet cable between the switch and the Sonos produced the best high frequency results. At the time, I didn't go with a shielded ethernet cable between the switch and the Sonos because the bass was lacking pitch definition with that arrangement. But with the "grounding plate" for the switch in place, the bass pitch definition is excellent. My conclusions... 1. The variation in the bass was a function of grounding the ethernet switch to a sufficiently large chassis, which was originally provided by the power conditioner and is now provided by the grounding plate. The variation in the bass was NOT due to the presence or absence of EARTH grounding, as I originally believed. 2. The variation in the highs was a function of the presence or absence of shielding in the ethernet cable between the switch and the Sonos. I suspect that shielding that cable reduces noise, either... (a) noise transmitted from upstream components (computer, switch) through the ethernet cables, or... (b) noise transmitted from nearby components (amp, preamp, Sonos, reclocker) through the air, or... (c) noise transmitted from downstream components (preamp, amp, power conditioner) through the ground wire between the switch and the power conditioner (that ground wire is now gone, but it was present on 3/3, when I experienced the same variation in the high frequencies). Not sure which of these was the culprit. Bryon |
03-04-12: Almarg I've been giving more thought to this, and I decided to experiment further with an alternative grounding scheme. I disconnected the ground wire between the ethernet switch and the power conditioner (thereby removing the switch's connection to earth ground), and I added a braided grounded strap between the ethernet switch and a 6" x 12" aluminum plate. My hope was that, by "enlarging" the surface area of the ethernet switch, it would provide more adequate dissipation of RFI or other noise picked up by the long ethernet cable between the computer and the switch. The results are at least as good, and possibly better, than the result of grounding the ethernet switch to the power conditioner (which, in turn, was grounded to the preamp, the amp, and earth). Bryon |
Hi Al -- I didn't realize from our earlier discussion that removing the PSU ground wire would reduce the level of noise filtering. Back it goes! Hi Mapman -- I've looked at Mu metal a few times. It seems like an interesting product. I elected to use TI Shield instead, along with regular old copper and steel. But I'll keep the Mu metal in mind for future diy projects. Thanks. Bryon |
I've applied mu metal foil that I was able to purchase on teh internet to shield my phono section from external EMI/RFI with good results. My understanding is mu metal is designed specifically for this kind of application. Check my "OHM Sweet OHM" system listing for pics of teh rather crude but effective mu metal enclosure I made around the Electrocompaniet step up transformer that I use with my low out mc cart and some discussion around same a couple years back. This effectively eliminated some external RMI/EMI issues from external devices that I was having with that particular device when I acquired it. |
Hi Bryon, I think we had concluded earlier that the ground wire connecting the PSU to the chassis was for the purpose of connecting filter capacitors between the chassis and each of the two AC input wires (hot and neutral). Therefore removing that ground wire will not create a safety hazard, but it may reduce to some degree the effectiveness with which noise entering the unit from the AC line is filtered. With the ground wire disconnected, what you have is the two capacitors in series (the series combination having a total capacitance equal to half of the capacitance of each of the capacitors) connected between the AC hot and AC neutral wires. That will provide some degree of noise filtering, but presumably less than if the ground wire were connected. Whether or not the difference in noise filtering might have any audible significance is not predictable with any certainty, as I'm sure you realize. Best, -- Al |
The Meridian G68 has a ground wire running from the IEC input to the chassis. As discussed in earlier posts, the G68's PSU has a SECOND ground wire that is also connected to the chassis, but at a different point. You can see a diagram here. You can see a picture of the PSU's ground wire here. Yesterday, while upgrading the AC wires running from the IEC input to the PSU, I removed the ground wire connecting the PSU to the chassis. The ground wire connecting the IEC input to the chassis is still in place. Works normally, but... Have I created a safety hazard? Thanks, Bryon |
I can't explain it either, Kijanki. I was just reporting what someone with a strong technical background and a distinguished track record designing this kind of stuff has said. It wouldn't surprise me if he couldn't explain it, either. One speculative possibility that occurs to me, though, is that if there is jitter at the output of whatever chip, or part of a chip, receives the incoming signal, noise transients corresponding in time to the jittery signal transitions at that point could (to some small extent) couple through the grounds or via other paths to circuit points that are downstream from the jitter reduction circuitry, ultimately affecting the timing of d/a conversion. That is perhaps a bit far-fetched, but it seems conceivable to me that it could be a perceivable effect with SOME equipment. As far as differences between lossless audio formats are concerned, see my thoughts here, and in my subsequent posts in that thread. Note that Steve N. (Audioengr) had some alternative thoughts. Best regards, -- Al |
Hi Bryon, My last post was not allowed. Probably because I referred to another audio site that has about 200 posts about the use of neodymium magnets. You have to experiment with them to find where the magnetic fields are emanating from in your system -- typically transformers in components and AC adapters. Then you let the magnets guide you to the "sweet spot". I use 1/8" x 1/2" neodymium magnets in bundles. They make a difference because they draw off the magnetic fields from the transformers. You place them on the outside of components and AC adapters. This has worked very well for me with SR MPCs that have a strong magnetic field. |
Al, I cannot hear any difference between different sources or cables with my jitter suppressing Benchmark DAC1. According to Benchmark and review measurements it provides very strong jitter reduction but few Audiogoners were able to detect sonic difference between cables or sources. It is hard to believe that anybody can hear -60dB suppressed by over 100dB (around 1kHz) but it is also very likely that my hearing (gear, room) is not that good. I don't question what other people can or cannot hear but am just trying to understand. On other thread people claim sonic difference between ALAC and AIFF (could you help with your computer expertise?) that again I cannot hear. Sometimes this whole high end audio is a little like black magic especially with grounding and shielding (I admire your persistence and patience Bryon). |
I also tried ferrites on the S/PDIF cable connecting the Sonos and the reclocker. That sounded bad. It made things sound hard and glassy. I suppose it elevated jitter.Yes, putting ferrites on digital signals for which jitter may be an issue is undesirable. The ferrites will filter out, or at least attenuate, the very high frequency spectral components of the signal, thereby slowing transition times between the 0 and 1 states and the 1 and 0 states (i.e., risetimes and falltimes). The slowed risetimes and falltimes will decrease the precision with which the receiving circuit can sense the specific voltage levels during those transitions that cause it to recognize that a 0 has changed to a 1, or vice versa. Jitter will thereby be increased. Ideally the reclocker would greatly minimize or eliminate the resulting jitter, but I recall Steve N. making the point that even where there is excellent jitter rejection capability there is usually still some benefit from minimization of jitter at the input. Best, -- Al |
03-25-12: Almarg That's an interesting hypothesis, Al. The mystery of ERS deepens. :-) 03-25-12: Lewinskih01 Hi Lewinski - I didn't select ferrites based on frequency, because I don't know the frequencies of the RFI I'm trying to reduce. So I took the shotgun approach and bought several different sizes like these from Parts Express. For some cables, I used multiple ferrites of different sizes in an attempt to cover a wider range of the frequency spectrum. I was a bit more scientific about where I placed the ferrites. I put them on... 1. Anything in the house that might pollute the power line... anything with a microprocessor, a switching mode power supply, a motor, a fan. So all appliances, tv's, computers, routers, dvr's, etc.. 2. Some of the power cables in the system. I started with all the power cables for equipment whose current draw is either relatively constant and/or unrelated to performance. So I put ferrites on the power cables for the computer, the disk drives, the Sonos, the reclocker, the ethernet switch, but NOT on the amp or the preamp. 3. The ethernet cables. 4. Some of the equipment grounds, including the chassis ground of the preamp and the signal ground of the amp. For this I made two RFI pigtails, which as Al and I discussed is probably nonsense, but they didn't do any harm and they were fun to make. 5. The ground wire of the Romex for the dedicated line to the system. Again, probably Black Magic, but with no ill effects. I also tried ferrites on the S/PDIF cable connecting the Sonos and the reclocker. That sounded bad. It made things sound hard and glassy. I suppose it elevated jitter. I did not try ferrites on the analog interconnects or the speaker cables. That seemed like a bad idea. Altogether, the ferrites resulted in a small but significant improvement in the system's noise floor, harmonic accuracy, and overall musicality. But be warned: Once you start, it is hard to stop. 03-26-12: Sabai Hi Sabai - This is new to me. Where do you put them? What size/shape/material? Do you know why they make a difference? Bryon |
Bryon, I am an inveterate tweaker. Neodymium magnets are among my favorite tweaks. I place them on or under components near transformers to draw off EMFs. The effect can be to increase the focus of instruments and voices and to provide a clearer sound than without the magnets in place. Yesterday I got a big surprise. I went around my system with a bundle of 4 neodymium magnets to see if I could feel any strong magnetic fields coming off of components or cables. I arrived at a Synergistic Research MPC. Lo and behold I felt a very strong magnetic field when the magnets came close to the MPC. I guess this should have been no surprise but I had just never got around to doing this kind of system test before. There was a spot on the back of the MPC where the magnets wanted to be. So I went through my system and let the magnets find their place on the back of 5 MPCs in my system -- mostly Galileo. I flipped my system breaker and when the first sounds came through my speakers I knew the magnets were making a real difference in the sound. Instruments and voices became more focussed as well as smoother. The soundstage became a tad more recessed but also somewhat deeper. The sound is now softer, more pleasing and more musical to my ears -- without any loss of resolution. I am using all of my reference CDs to test this today and the results are uniformly good. |
Bryon, Been following and learning from this thread. Thanks for keeping it going! I'm getting the itch to try some of these. The ferrites seem like the easiest place to start. I understand ferrites need to be carefully chosen by frequency. Which ferrites did you choose and why, and which were the most effective places for them? Cheers! |
Bryon, an additional point occurs to me regarding the ERS cloth. Since its core is somewhat conductive, if it is placed close to circuitry (significantly closer than the metallic structural surfaces of the component), its presence could affect the amount of stray capacitance between arbitrary circuit points. It could therefore conceivably have effects via mechanisms that are unrelated to RFI. How close is "close" is unpredictable, and would be dependent on the particular circuits and circuit points that are involved. The effects that would result, if any, would also be unpredictable. In general, I would guess that the circuit points that would be most sensitive to those effects would be certain kinds of analog circuit points, such as what are known as summing junctions, and other points that are within feedback loops. Best, -- Al |
Thanks, Al, for your explanation of the signal ground binding post on the amp. Your hypothesis about the ERS is interesting. I plan on removing it from the G68 temporarily to see if things get better or worse, now that I've made so many other changes to the G68 and the rest of the system. I will report back the result. I might post my findings in the Magic thread, since (I now recall) that's where most of the discussion of ERS occurred. RFI pigtails can IMO be placed somewhere close to the border separating the remotely plausible from the totally preposterous. That made me laugh. And I'm not surprised to hear you say it. I suspected as much. It's strange the things you will do when in the grip of addiction. :-) I looked at the thread you linked. An interesting discussion of another Magical device, if you can call a piece of wire a 'device.' All your skeptical comments make perfect sense. Still, after reading that thread, I want to try it. One day at a time. One day at a time. Bryon |
Hi Bryon, Re your three updates: 1)One possible explanation would be that where the cloth produced a negative result it might have been deflecting radiated rfi into sensitive circuit points which the rfi would not otherwise reach. Another possibility is that at some locations the cloth reduced jitter that may have been euphonic. In Steve N.'s paper that I linked to in my post dated 2-8-12, he describes how jitter can sometimes be euphonic in character. 2)Good! 3)The signal ground post on the amp would be needed if a powered sub having speaker-level inputs were connected to the amp's outputs. Since the amp's outputs are balanced, its negative output terminals have a signal on them, rather than being ground, and so the negative speaker-level input terminals of a powered sub should not be connected to those terminals. A chassis screw can be used as a ground connection point on some amps, but not on your Pass because signal ground and chassis are not common. They are connected together through a power thermistor (thermal resistor). RFI pigtails can IMO be placed somewhere close to the border separating the remotely plausible from the totally preposterous. Which is to say that I wouldn't completely rule out the possibility that under some circumstances they might have at least a miniscule effect. I would bet against it, though. You may find the comments by me and others in this thread to be of interest. The pigtail shown in your photo differs from the kind that is addressed in that thread, in part because yours appears to wrap the wire around a ferrite. The ferrite would raise the impedance of the wire at very high frequencies, which would alter the frequencies at which any antenna effects might occur. Whether that would be for the better, for the worse, or would make no difference, relative to having no ferrite on the pigtail, is anyone's guess. My guess is that it would make no difference. IMO. Best, -- Al |
Update. Three things... 1. After further experiments with additional ERS cloth, placing it in every location I could think of, I have come to the conclusion that, in my system, to my ears, it is harmful more than helpful about 90% of the time. Some folks predicted I would say that. You were right. It has a tendency to make things sound strangely "muffled." I find that just as puzzling as my initial impression that, in my dac, it resulted in a slight improvement in sound quality. I have not yet removed it from the dac to see if my impression might have changed. That is certainly possible, especially in light of the extensive tweaks I've made to reduce RFI/EMI in the system since I initially installed the ERS. 2. I am happy to report that, with the loving support of my wife and timely medical intervention, I have overcome a three week addiction to ferrites. :-) There are now approximately 50 ferrites all over the house. I attached them to things that pollute the power lines, as well as to some of the cables in the system, including the ethernet cables. I did NOT attach them to the system's interconnects, speaker cables, or power cables. I must say, they really work, provided you don't put them in the wrong place. 3. Among my final experiments with ferrites was to create two RFI pigtails. They look like this. I attached one pigtail to the chassis ground of the Meridian G68 and a second pigtail to the signal ground of the amp (which was made easy because Pass includes a signal ground binding post on the rear of the amp, for reasons that are unclear to me). I have no idea whether the RFI pigtails make a difference. I probably should have posted this part in the thread on Magic. Perhaps someone can comment on whether the whole idea of an RFI pigtail is preposterous. Bryon |
Would it be effective, and is it safe, to put a ferrite on the GROUND WIRE of the system's dedicated AC line?Hi Bryon, I don't see any problem with that, although I have no idea as to whether or not it will provide a benefit. As you no doubt realize, what it will do is to raise the degree to which the the flow of currents that are at and above some frequency in the RF region is resisted. That should be no problem either under normal circumstances or under fault conditions that would require the breaker to trip. Best, -- Al |
I've been putting the finishing touches on reducing the effects of EMI/RFI by putting ferrites on things. I've put some ferrites on power cords in the system (only on components whose performance is not affected by current draw). I've also been wandering around the house, putting ferrites on things that dump RFI onto the power lines. Question: Would it be effective, and is it safe, to put a ferrite on the GROUND WIRE of the system's dedicated AC line? Bryon |
Thanks, Al. Everything you said makes sense. It's interesting that you took Dr. Johnson's course. It looks very interesting, although most of it would go way over my head. Let me take this opportunity to say that, during this process, you've been an invaluable source of information, advice, and support. It is VERY appreciated! I will now resume the rest of my life. My wife is expecting our first baby any day now, so I finished this experiment just in the nick of time! :-) Bryon |
Hi Bryon, Good find. Whatever Dr. Johnson says, is so! He is one of the world's leading experts on high speed digital signal transmission. As it happens, I took his course on high speed digital design about 15 years ago, in connection with my job. This is the associated textbook. You'll be amused at its sub-title, "a handbook of black magic." As you certainly realize at this point, grounding and shielding are among THE most arcane and mysterious aspects of electrical engineering, with problems often being resolved by not much more than blind trial and error. I, btw, am by no means an expert in that area. With respect to the second paragraph of your post just above, where you said "correct me if I am wrong," I believe that everything you said is correct. With respect to the apparent paradox cited at the end of your post, I believe that two things need to be considered. First, for shielding to be effective at high frequencies, as Dr. Johnson indicated the shield should be grounded at both ends. But I believe that the key element of what he is referring to by "grounding" is a connection at each end between the shield and the metallic structure of the component, rather than a connection to some external ground point. I believe that circulation of noise currents from the cable shield into the metallic structure of the components will dissipate their energy significantly, although perhaps less so in the case of the network switch due to its small size. Second, concerning the improvement you noted when connecting the 14 gauge ground wire to the network switch, my speculation is essentially as I commented yesterday: Lower frequency grunge presumably was also present, perhaps associated with the computer's switching power supply, power line distortion, emi pickup, etc, the effects of which may not have been entirely eliminated by the reclocker. Your ground connection is presumably a much better conductor at those lower frequencies than at the very high signal-related frequencies ...You were probably reducing the amount of low frequency noise that had been present at that point (the sources of that noise being unrelated to the ethernet signals themselves), that was making its way through the circuit grounds downstream, resulting in jitter that was not being entirely eliminated by the reclocker. All that is obviously fairly speculative, but those are the only explanations I can think of that seem to fit all the facts. Best, -- Al |
Hi Al - I checked for continuity between the tabs in the computer's ethernet port and the computer's IEC ground pin. You were right, the port is grounded. Correct me if I am wrong, Al, but that seems to help explain something that puzzled me at the time: the dramatic improvement I heard when I first replaced the unshielded ethernet cables with shielded ones. In my posts on 2/16, I was mystified about how a $7 cable could make such a difference. You offered me a speculative explanation at the time, but I was left with a certain amount of puzzlement. What I didn't know at the time (but you did) was that the shielded ethernet cable was also grounded. Knowing that now, it seems to help explain how I could have heard such a dramatic improvement. There is one other point I've been wondering about with respect to ethernet grounding, and that is: Is it better to ground an ethernet cable at both ends? I poked around a little and I found a discussion of this topic, in which an evident expert said this... In high-speed digital applications, a low impedance connection between the shield and the equipment chassis *at both ends* is required in order for the shield to do its job... One thing I'm still unclear about is whether the grounding I've created at both ends of my 50' ethernet cable is "operative over the frequency range of [the] digital signals." I know you said that... the inductance of a plain piece of wire will cause it to have a significant impedance at the high RF frequencies that constitute the spectral components of the ethernet signals. ...which, in combination with the information I quoted above, seems to suggest that grounding the ethernet cable at both ends should have no additional benefit. But I DID hear an additional benefit when grounding it at both ends. Perhaps that is because, as you said... the resistance of the very long run presumably lessens the effectiveness of that ground from the perspective of the switch. ...but I'm not sure I completely understand how that works. In other words, I'm unclear about how the following 3 things can all be true at the same time: 1. The effectiveness of a ground method for an ethernet cable's shield depends upon whether the ground method operates over the frequency range of the ethernet signal. 2. The ground method I provided my ethernet cable (at the switch) is ineffective at the frequencies range of the ethernet signal. 3. I heard an improvement when grounding the ethernet cable at *both* ends. Assuming I'm right about #3, maybe you can say a few more words about how those things can all be true. Thanks! Bryon |
Hi Bryon, The 14 gauge wire is certainly an "effective path" at low frequencies, and probably at frequencies ranging up into the ultrasonic and perhaps low RF region. But the inductance of a plain piece of wire will cause it to have a significant impedance at the high RF frequencies that constitute the spectral components of the ethernet signals. It will therefore not conduct those frequencies effectively. The impedance that is presented by inductance, as measured in ohms, is directly proportional to frequency. The inductance, btw, is directly proportional to length. As I mentioned, for good conduction of RF frequencies to ground a braided ground strap, such as this, is needed. However I suspect that if you were to use a braided ground strap on both the network switch and the G68 you would wind up with worse results, because it would create a path that would conduct RF noise from the switch to the ground point, and from there to the G68, bypassing the reclocker. Also, you mentioned that the shield of the 50' ethernet cable is grounded at the computer end. I couldn't find any information about that online. How can you tell?I should perhaps have qualified my comment by saying that that is the case with the desktop computers that I am familiar with, which primarily means those I have built myself using Asus and Gigabyte motherboards. On those motherboards, at least, shielded jacks are provided for the ethernet ports, the shields in turn being connected to the circuit ground on the board, which in turn is connected to the metal case of the computer and to AC safety ground. It's easy enough to verify that on your particular computer. Disconnect the ethernet cable from the computer, and look for two small metal tabs on either side of the jack. Check for continuity from one of those tabs to the computer case and/or to the AC safety ground pin on the computer's power connector. Best, -- Al |
Thanks again, Al. A few final questions... You mentioned a couple times that a ground must have an "effective path." I don't really know what the factors are that make a ground path effective. To ground the ethernet switch, I drilled through the metallic housing of the block of ethernet ports and connected a 14 gauge wire. The wire runs to an aluminum screw that passes through the switch's housing. You can see a picture here. A second 14 gauge wire runs from the switch to a screw on the power conditioner. Does that seem like an effective path? Also, you mentioned that the shield of the 50' ethernet cable is grounded at the computer end. I couldn't find any information about that online. How can you tell? Bryon |
