Thanks, Al, for that detailed response. I'm in the middle of a long series of tests, trying to determine the best grounding arrangement. I will report back when the results are in.
Bryon
Bryon
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 posts total
Here are the results of my experiments with grounding
THE SETUP COMPUTER -> 50 shielded ethernet cable -> ETHERNET SWITCH -> 1 ethernet cable -> SONOS -> s/pdif cable -> RECLOCKER -> s/pdif cable -> MERIDIAN G68 -> analog interconnect -> PASS AMP THE EARTH GROUNDS computer: grounded to circuit #1 ethernet switch: NOT grounded Sonos: NOT grounded reclocker: NOT grounded Meridian G68: grounded to circuit #2 Pass amp: grounded to circuit #2 Other than the computer, all the above components are plugged into a single Shunyata power conditioner, which is itself plugged into circuit #2 (a dedicated line). THE EXPERIMENT I manipulated 2 variables. First variable: grounding vs. not grounding the ethernet switch. Second variable: using a shielded vs. unshielded ethernet cable for the 1 run between the ethernet switch and the Sonos. I tested 4 arrangements: 1. UNGROUNDED switch + UNSHIELDED cable 2. UNGROUNDED switch + SHIELDED cable 3. GROUNDED switch + UNSHIELDED cable 4. GROUNDED switch + SHIELDED cable I tested for continuity (from the ethernet switch to all other components), and I also did listening tests for each arrangement. Important point: For ALL arrangements, the 50 ethernet cable between the computer and the ethernet switch was SHIELDED. I only tested the shielded vs. unshielded ethernet cable for the 1 cable between the ethernet switch and the Sonos, which as you will see, changed both the continuity results and the listening results. THE CONTINUITY RESULTS 1. UNGROUNDED switch + UNSHIELDED cable Ethernet switch to Sonos input NO continuity Ethernet switch to Sonos output NO continuity Ethernet switch to reclocker input NO conitnuity Ethernet switch to reclocker output NO continuity Ethernet switch to Meridian G68 NO continuity Ethernet switch to Pass amp NO continuity 2. UNGROUNDED switch + SHIELDED cable 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 3. GROUNDED switch + UNSHIELDED cable 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 4. GROUNDED switch + SHIELDED cable Ethernet switch to Sonos input continuous Ethernet switch to Sonos output continuous Ethernet switch to reclocker input continuous Ethernet switch to reclocker output continuous Ethernet switch to Meridian G68 continuous Ethernet switch to Pass amp continuous THE LISTENING RESULTS 1. UNGROUNDED switch + UNSHIELDED cable Lacking pitch definition in bass. 2. UNGROUNDED switch + SHIELDED cable Lacking pitch definition in bass. Little or no perceptible difference from arrangement #1. 3. GROUNDED switch + UNSHIELDED cable Excellent. The best arrangement by a considerable margin. Very good pitch definition in bass. 4. GROUNDED switch + SHIELDED cable Better highs than arrangement #1 or #2, but like #1 and #2, still lacking pitch definition in bass. MY INTERPRETATION OF THE RESULTS 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 using a shielded ethernet cable between the ethernet switch and the Sonos resulted in poorer performance because, as you speculated Al, it defeated the galvanic isolation in the reclocker. It's worth pointing out that I did NOT hear a difference in the noise floor among ANY of the arrangements. I tested this by turning up the G68's volume to max and putting my ear to the tweeter. Because of this, I suspect that the main audible variation I heard pitch definition in bass was attributable to differences in jitter levels among the various grounding arrangements. I believe I have read that jitter can be audible as a lack of bass pitch definition. That could have been from Steve N., or some other source, Im not sure. This has been an informative experiment for me. For one thing, I didnt expect to hear a difference in bass response at all. Also, before the experiment, I would have guessed that arrangement #4 (grounded switch + shielded cable) would yield the best results, because I naively assumed that the more grounding/shielding the better. That was true only up to a point. Bryon |
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: AlmargI 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 |
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 |
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 |
- 115 posts total