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 |
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 |
The only thing in the chain without shielded ports is the router. So I plugged in both ethernet cords next to each other and then wedged in a scew between the metal shields on the RJ45 plugs to tie their shields together. Does anybody think that will work? I doubt that is necessary. As long as the shields are grounded at one end, I would think that should be sufficient. And I would expect that which end is grounded doesn't matter, since what you are trying to do is to prevent rfi from escaping from the cable. In other situations, as you may realize, if the signal flow is unidirectional and only one end of the cable shield is grounded it is generally desirable for that to be the source end, so that rfi that may be picked up won't be conducted to the destination component. But that is not applicable in this situation, because rfi pickup is not the concern (and probably also because the link is bidirectional). Regards, -- Al |
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 |
Thanks Jim!
Best regards,
-- Al |
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 |
Hi Bryon,
Yes, you're right. After looking at the photos I believe that the two small blue objects just above the green wire are capacitors that are provided for purposes of filtering high frequency noise that may be present on the incoming AC. One capacitor is probably connected between AC hot and chassis, and the other capacitor between AC neutral and chassis, with the green wire providing the connection to chassis for both capacitors.
Ergo, not a problem!
Best,
-- Al |
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 |
Hi Bryon,
Presumably the shielded cable is reducing the amount of rfi/emi that escapes from the cable and couples onto circuit points elsewhere in the system, most likely points that are "after" the reclocker circuitry. There are probably a number of ways in which that could occur, despite the shielding you have incorporated into the G68. One possibility would be that it couples onto the power wiring, and makes its way from there onto the grounds within the G68. Noisy grounds in the digital section could (and probably would) result in increased jitter. Noisy grounds in the analog circuitry would have unpredictable but conceivably significant consequences at audible frequencies, even if the noise itself is at rf frequencies (as a result of intermodulation, AM detection, or other effects that can cause rfi to affect audible frequencies).
That's my speculation, anyway.
Best,
-- Al |
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 |
Outstanding, Bryon! Glad all this work has paid off. Enjoy!
Best regards,
-- Al |
Hi Bryon, I'm not sure that connecting the chassis of the network switch to some ground would accomplish anything. And conceivably it could even be counter-productive, because it might create a ground path that would bypass the galvanic isolation that is provided in Steve's reclocker. One reason that it would tend not to accomplish anything is that the inductance of the ground wire would make it an ineffective conductor of high frequency (RF) energy, which is what you are attempting to dissipate in this case. Or do the ethernet PORTS themselves have to shielded/grounded in order to pass the benefits of grounding on to the cables? I don't think so, beyond the shielding and grounding provisions that appear to already be provided for the ports in the network switch and the Sonos. Presumably the shields of the ethernet cables are connected to the metallic shells of their plugs, which in turn contact the metallic shields of the mating connectors on the network switch, which in turn contact the metallic housing of the switch. A low impedance path will also exist from there to the chassis of the Sonos ZP90, through the shield of the ethernet cable connecting the switch to the Sonos. The Sonos appears to also use a shielded ethernet connector, based on a photo I found at the Sonos site. Presumably and hopefully whatever RF energy is picked up by the shields of the ethernet cables from the conductors they contain will be dissipated effectively in the metallic structures of the two components, and perhaps also further upstream. Those are my tentative thoughts, anyway. Perhaps Jim or Kijanki or one of the others who have been participating will comment further. Best, -- Al |
Well done, Bryon, and also very well described. I suspect that grounding the ethernet switch resulted in significant benefits because it grounded the shield for the 50 shielded ethernet cable running between the computer and the switch. I suspect that you're right. The shield is grounded at the other end, via the computer, but the resistance of the very long run presumably lessens the effectiveness of that ground from the perspective of the switch. 02-29-12: Almarg
One reason that [grounding the switch] would tend not to accomplish anything is that the inductance of the ground wire would make it an ineffective conductor of high frequency (RF) energy, which is what you are attempting to dissipate in this case.... Presumably and hopefully whatever RF energy is picked up by the shields of the ethernet cables from the conductors they contain will be dissipated effectively in the metallic structures of the two components, and perhaps also further upstream. I was perhaps focusing too narrowly in these statements on RF noise related to the high frequency and very fast risetimes and falltimes of the signals being conducted by the long cable, and the need to prevent that noise from radiating from the cable to other points in the system. 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 (for which a braided ground strap would be necessary to provide an effective path, although doing that could very conceivably worsen the results by providing a path for RF noise to bypass the reclocker and get into the G68). In any event, congratulations on the excellent improvement! Best, -- Al |
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 |
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 |
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 |
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 |
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 |
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 |
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 |
Sounds good! With respect to placement of the plate, if you haven't already done so it might be worth trying it positioned directly under the switch.
Best,
-- 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? 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 |
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 particularly enjoyed this one. LOL! I hadn't seen that before. Thanks! Best regards, -- Al |
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 |
