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Old 7th April 2007, 01:34 PM   #1
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Default active shielded speaker cables

well this might also fit in this section....

Does anybody knows anything - or has some schematics related to speaker cables that have avtive shielding ....something related to canceling capacitances or something...
i am interested in this thematic - i have a double coaxial speaker cables that might be used to try this method....
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Old 7th April 2007, 04:04 PM   #2
flg is offline flg  United States
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I have worked with equipment, from a different field, That had to drive analog signals 20-30' down a cable. We used a double shielded cable. The inner shield was driven by a low power amp driving the same signal as the signal line. The outer shield was a gnd'ed shield. The theory here is that the signal line is in effect "cascoded" by the inner shield. With almost the same potential from the signal line to the inner shield, there is no charge, no capacitance. The inner shield amp had to deal with the capacitance to the grounded shield. Although not a perfect amp, or as accurate as the signal amp, it provides a 98% improvement for the envirenment of the signal carrying line.
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Old 7th April 2007, 04:31 PM   #3
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thanks FLG, well, i have only one shield .....
i wonder what Audioquest is doing with their cables and also Synergestic Research with their Active Shielding.....that is the reason...
i have only one shielding - so i can't make Your suggestion work....but i think that something similar is what they are using but i am not fully sure.....

any other suggestions - or something how to modify this first one ...
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Old 7th April 2007, 09:58 PM   #4
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Quote:
Originally posted by sunrise
thanks FLG, well, i have only one shield .....
i wonder what Audioquest is doing with their cables and also Synergestic Research with their Active Shielding [...] any other suggestions - or something how to modify this first one ...
What they do with their Active Shielding is something known as "marketing".

If you want a decent shielded speaker cable, try four mini-GR-8 with all shields in parallel and all cores in parallel. The equivalent capacitance will be about 120 pF/ft, or about .001 uF for an 8 foot run. Series inductance will be about 18 nH/foot, or about 150 nH for 8 feet, low enough even for difficult loads. Series resistance will be about 20 milliohms for 8 feet.

It turns out shielded speaker cables can help under some circumstances such as noisy RF environments, perhaps because less junk is coupled back to the feedback loop.
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Old 8th April 2007, 07:14 AM   #5
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still i want to try this on my cables that are in my system .....
so i am still waiting to see if somebody has been working with the idea and has some more informs to help me....
thanks DSP_geek
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Old 8th April 2007, 03:31 PM   #6
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I guess I am missing something.
The impedance on the amp-to-speaker wire is relatively low. Do you think you are picking up noise or RFI? I am not being argumentative, I am simply skeptical.
-Tom
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Old 8th April 2007, 03:50 PM   #7
phn is offline phn  Sweden
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Audioquest tried it.

Art Dudley of Stereophile wasn't impressed: "My belief is that their 'dielectric bias' system, which I wound up removing and leaving in my desk drawer, has no influence on their performance one way or the other."

http://www.stereophile.com/cables/804aq/index.html
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Old 8th April 2007, 05:46 PM   #8
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PrestonTom - i do want to get rid of anything that might affect the sound in my cables - that also includes RFI.....
but i also wants to get rid of the capacitance that speaker (or interconnect) cable has.....
That is why i want to make something that will insert the signal also on the shielding in order that i loose that capacitance - that is done (from the informations that i have) by using some opamp and some kind of circuit and very low currents....
i don't know how this circuit is looking so i need somebody that has some experience with this problem to help me with the circuit

i don't want to invent some circuit that is completely new but to use the technology that people use in the situations where they want to get rid of those pharasythic capacitances in speaker (or interconnect) wires if those wires are coaxial types.....

edit: phn....what Audioquest did is intersting too but i don't think that they want to get rid of that capacitance of the cable - they were thinking probably to build something like people use for anthena's on TV sets...but i am also not sure how this circuit is looking to.....sorry...that is why i have asked if anybody know this too.....


first what i want to do is to get rid of the capacitance of the cable.....first thing ....
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Old 9th April 2007, 10:34 AM   #9
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o.k. - so far i have found that i need unity gain opamp that be stable at unity gains, that will have reasonable slew rate and that will be able to work on high input voltages (up to +/-40 or 50V)
the schematic is attached...
can anybody help me with the opamp....
it needs to withstand the voltage at the output of the power amplifier (lets say that amplifier is arround 50-70W), it needs to be unity gain stable and also have rail-to-rail input/output topology or at least common mode input voltage range and output swing in the voltage range of the signal from the output of the power amp.....
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File Type: jpg drawing1.jpg (21.4 KB, 318 views)
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Old 9th April 2007, 11:00 AM   #10
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discrete amp will surely be easier to make than trying to find a +-50V opamp.
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