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Old 14th May 2013, 05:41 AM   #21
paulfx is offline paulfx  United States
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I've now got the 4 gauge ground strap cable. Now to fix it so there is one and only the one ground/earth connection between each chassis. By the way, can anyone tell me the best way to interrupt the ground on an HDMI cable?
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Old 14th May 2013, 05:55 AM   #22
paulfx is offline paulfx  United States
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Or I should say, the grounds on HDMI...on Wikipedia there is a pin-out chart and it appears pins 2, 5, 8, 11 and 17 in addition to the shield around the whole cable would have to be severed on one end. Maybe I could get a short extension HDMI cable to experiment with?
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Old 14th May 2013, 09:41 AM   #23
AndrewT is offline AndrewT  Scotland
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No.
the intervening ground(Returns) in the HDMI cable are mandatory for the proper low impedance of the signal pairs. The cable MUST operate at VHF and at these VHF frequencies the IMPEDANCE of the signal pair is vitally important. Closeness of the Signal HOT to Signal Return determines the inductance of the Signal Pair. That inductance must be low to preserve the digital rise/fall times.
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Old 16th May 2013, 11:01 PM   #24
paulfx is offline paulfx  United States
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Here is another thread on HDMI ground loops:
How to break possible HDMI ground loops
AndrewT, I see your point about returns in each signal pair - they are designed for a specific twist rate, and a certain thickness so as not to have phase errors at the bit stream frequencies. Screwing around with their shields might not be productive. I wonder if those 4 HDMI shields and 1 earth return have low enough impedance at audio frequencies to even pass audible ground loop currents.
I think I'll interrupt only the outer earth/ground shield at one end of each HDMI cable, and leave the signal bundle alone. Pins 1-19 I will look at as one signal lead. After connecting the whole system, I will measure AC voltage at the speaker outputs with and then without the HDMI cables to see it there is any difference.
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Old 17th May 2013, 06:45 AM   #25
marce is offline marce  United Kingdom
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http://www.hottconsultants.com/pdf_files/aes-2007.pdf
Designing for Interference-free Audio System Components
A Practical Interference Free Audio System (Part 2)
Bonding Cable Shields at Both Ends to Reduce Noise
We have to assemble systems in the non diy world where you have to have a direct PE connection, no circuitry between PE and the equipment.
Cables have to be connected at BOTH ends for shielding, otherwise it doesn't shield, especially at RF frequencies.
Quite often the problem is the lower frequencies (the hum) following a path you didn't know was there, as they tend to follow a different path to the HF stuff.
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Old 18th May 2013, 11:35 PM   #26
paulfx is offline paulfx  United States
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Thanks, marce, I'm reading Ott
http://www.hottconsultants.com/pdf_files/aes-2007.pdf
and in slide 22 he answers my question: How do I get my single-end coax cable to act as if the shield is connected at both ends at the RF spectrum so it doesn't act like an antenna, and at the same time have an unconnected shield at low audio frequencies? Answer: Hybrid grounding.
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Old 18th May 2013, 11:40 PM   #27
paulfx is offline paulfx  United States
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Slide 23 in Ott AES 2007 has the elegant diagram.
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Old 20th May 2013, 07:20 AM   #28
paulfx is offline paulfx  United States
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Default Partial Ground Lift

Looking around some more, a cap alone would decrease shield current all the way down in frequency at 6 db per octave. In "Ground Lift"

Groundloop problem solving: Ground lift circuits

Tomi Engdahl recommends a cap for single end lines like Ott:
. Signal --------------------- Signal
. Ground -------||----------- Ground
................... 10 nF

In the same article Engdahl adds a resistor in parallel for balanced connections:

Partial ground lift with RFI filtering for balanced XLR connectors
...............+--||--+
...............| _____|
...1 ------+-|____|+--- 1
.................100 ohm
...2 ------------------ 2
...3 ------------------ 3

Couldn't I do this at the far end of each single-end connection between chassis?
..Signal -------------------- Signal
......................10 nF
..................+---||---+
..................|.______.|
..Ground ----+-|____|-+--- Ground
....................100 ohm
-Assuming, of course, my 4 AWG PEC also runs between them?
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Old 22nd May 2013, 10:38 PM   #29
paulfx is offline paulfx  United States
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Assuming each input or load is 25K ohms, and I would like high pass with -3db at 200KHz, C=1/(2pi*f*R)=31.8 pF, or 32pF, then for the far end of each coax:

..Signal -------------------- Signal

......................32 pF
..................+---||---+
..................|. _____. |
..Ground ----+-|____|-+--- Ground
....................200 ohm

This would allow current to flow through the shields at RFI frequencies, but very little to flow at 60Hz or 120Hz. Most all of the current would go through the big fat parallel earth connection.

What do you guys think - Is there any way this setup could affect the audible spectrum? Would it be worth it to get high-quality caps at these small values, maybe like they used to use to adjust capacitance of phono cartridges?
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Old 24th May 2013, 05:39 PM   #30
paulfx is offline paulfx  United States
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Default Neutrik NC3MXX-EMC

Arguing with myself again, but here is the Neutrik NC3MXX-EMC balanced connector, which uses a coaxial cap of 4pF or less (along with an inductor):

Mine will be cruder, a cap and a resistor on the receiving end of each unbalanced connection.
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