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Old 27th June 2010, 03:14 PM   #1
neazoi is offline neazoi  Greece
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Default An ultra Low Shunt Capacitance way for audio interconnections (LSC configuration)

An idea,
K.Giannopoulos official site
I would like your comments
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Old 27th June 2010, 05:29 PM   #2
gootee is offline gootee  United States
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It seems like it could be good.

But I don't know what the magnitude of the effect of the shunt capacitance is, or how much this might change it.

Do you have any related measurements?
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Old 27th June 2010, 05:51 PM   #3
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Not sure shunt capacitance is a problem at all unless the cable is very long . All my interconnects with the exception of the arm to phono are not screened anyway and moving coil cartridges are not very sensitive to shunt capacitance.
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Old 27th June 2010, 06:18 PM   #4
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Using this arrangement, we transform the coaxial into a parallel set of cables, each of them having its own shield. The un-connected shield will still provide some short of shielding from the high frequency radio waves, but of course not so strong shielding as if it was connected to the ground.
Do you have any measurements or theory to back this up?

Surely what you are doing is identical to using a single coax cable and insulated sockets.
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Old 27th June 2010, 07:58 PM   #5
neazoi is offline neazoi  Greece
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Originally Posted by richie00boy View Post
Do you have any measurements or theory to back this up?

Surely what you are doing is identical to using a single coax cable and insulated sockets.
Well not exactly.

In a single coaxial cable and insulated connectors, the ground is the shield of the cable and it is connected to the central GND at some point. The cable then still behaves like a capacitor with the internal conductor being the one plate and the shield being the second plate of the capacitor.

In the case where two coaxial cables are used to transfer the positive and GND of the signal in their internal conductors and the shields are connected to ground, there will still be shunt capacitance on the coaxial transfering the positive but not in the coaxial transfering the GND (if someone could use the term "transfering"..)

In the refered case, two coaxials are used for each channel. The shields are left unconnected on both, and the positive and negative signals pass only through the internal conductors, pretty much like your parallel pair of your speaker cables.
The unconnected shields form a kind of shielding which reflects the radio waves like a microwave dish reflects (and focuses) the radio waves into the desired direction.

Basic capacitor theory applies here, nothing special. If you leave one plate of a capacitor unconnected, you do not have a capacitor!

Imagine it like having a single wire which resides (and does not touch) inside a water pipe, the water pipe not being connected to the GND. No RF passes into the wire.
Another way to imagine it is to imagine it would be to tie an insulated wire with a piece of aluminum sheet, the aluminum sheet not connected to ground.
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Old 27th June 2010, 08:02 PM   #6
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The idea is sound, and therefor (sorry...) has been tried before. You can buy cables that have two twisted wires that carry the 'hot' and signal gnd, overall screened with a screen that is either connected on one side only or on both sides (in the first case, often an arrow on the cable indicates where the screen is connected to ground). In fact this is even better than two separate cables as is proposed: the twisting of the two wires keeps them close together so that any interference tends to be the same in both, so the effective interference (the difference between the two) is minimized.
Of course, it's only one more step to balanced cables....

jd
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Old 27th June 2010, 08:03 PM   #7
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Originally Posted by gootee View Post
It seems like it could be good.

But I don't know what the magnitude of the effect of the shunt capacitance is, or how much this might change it.

Do you have any related measurements?
I am not able to measure so low capacitances like the shunt capacitance of a low length coaxial, however basic capacitor theory shows that a capacitor with one plate left unconnected is not a capacitor.

To my taste, shunt capacitance introduced by cabling has little effect though and it is of considering only if the whole audio system has been designed in a perfectionist sense or if cable lengths are quite long.
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Old 27th June 2010, 08:09 PM   #8
neazoi is offline neazoi  Greece
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Originally Posted by janneman View Post
The idea is sound, and therefor (sorry...) has been tried before. You can buy cables that have two twisted wires that carry the 'hot' and signal gnd, overall screened with a screen that is either connected on one side only or on both sides (in the first case, often an arrow on the cable indicates where the screen is connected to ground). In fact this is even better than two separate cables as is proposed: the twisting of the two wires keeps them close together so that any interference tends to be the same in both, so the effective interference (the difference between the two) is minimized.
Of course, it's only one more step to balanced cables....

jd
I see what you mean,
The balanced technique is used in UTP computer networks too for noise cancelation, but in not op-amp based audio I think there is no way to cancel this noise even if the cables are twisted (not entirely sure).

On the other side twisted pairs carying +/- sig still introduce some capacitance, each conductor is the plate and the insulation being the dielectric. The capacitance is much lower than coaxial cables though.

I am talking about a cheap way to achieve highly desirable characteristics. There is no lower capacitance than two wires not touching each other.
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Old 28th June 2010, 07:00 AM   #9
RJM1 is online now RJM1  United States
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The problem that I see with this is that if the shield of the coax is not connected to ground at either end it essentially becomes an antenna that is capacitive coupled to the center conductor. With the coax shields greater cross sectional area it will pick up more RF than a wire the same size as the center conductor and transfer the RF energy to the center conductor. This I think would make you more susceptible to RF than an unshielded 22awg wire.
Oh, and two wires not touching each other is basically the description of a capacitor.
(two conductors separated by a dialectric)

Last edited by RJM1; 28th June 2010 at 07:04 AM.
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Old 28th June 2010, 08:28 AM   #10
neazoi is offline neazoi  Greece
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Originally Posted by RJM1 View Post
The problem that I see with this is that if the shield of the coax is not connected to ground at either end it essentially becomes an antenna that is capacitive coupled to the center conductor. With the coax shields greater cross sectional area it will pick up more RF than a wire the same size as the center conductor and transfer the RF energy to the center conductor. This I think would make you more susceptible to RF than an unshielded 22awg wire.
Oh, and two wires not touching each other is basically the description of a capacitor.
> and two wires not touching each other is basically the description of a capacitor.
Yes of course, the capacitance is too low in air dielectric so it is not of much importance here.

I have never thought it that way, It is like having a transmitter microwave dish radiate backwards? It does not make sense to me if comparing it with a dish, but your acquisation is completely right for longer wavelength RF. The shield becomes an antenna which picks up RF and capacitivelly couples it to the internal conductor.

Although for microwave frequencies it may actually repel RF, as any metalic object acts like a mirror for microwaves either connected to ground or not. Also, this coupling capacitor behaves like a high pass filter which cutts-off completely the lower frequencies if the capacitance is too low.

Combined these two effects (cutt-off for low frequency RF, and mirror for microwaves) should give the desired result of moddest shielding, although one should use low capacitance coaxial cable to ensure higher cut-off.

Does it make sense?
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