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Old 11th February 2003, 05:01 PM   #1
cowanrg is offline cowanrg  United States
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Default Synergistic Research Active Shielding?

hey guys. I was over at a high end store today and noticed once again synergistic research's active shielding. im wondering if anyone has any ideas as to what this is/does? im thinking its two copper braids around a dielectric shield (copper > dielectric > copper) over the cable... one copper shield is positive, and the other negative, and at one end is a load source (LED), and at the other end is an adapter that connects to a DC power source that feeds it power. the guys say it just comes with a wall wart and you just plug it in. there is NO electronics on it it seems.

and the whole active shielding is away from the signal source. so they arent connected in any way. they can add the shielding to any existing cable. from a technical standpoint, it should make a difference if a shielded cable benefits your system...

i just bought some really really super duper nice tara labs cable for $60 that i wouldnt mind adding some active shielding to. also some old audioquest too...
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Old 11th February 2003, 05:18 PM   #2
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I don't exactly know what Synergistic does on their active shielding, but generally this is a very old trick to eliminate problems caused by the capacitance in a shielded cable.

The trick is to feed the buffered signal voltage to the shield. As there will be no differential voltage between shield and signal conductor, all negative effects of the capacitance will be gone.
But this is certainly impossible without any electronics - you need an active buffer circuit.

Nevertheless perhaps a good idea for a diy interconnect.
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Old 11th February 2003, 05:26 PM   #3
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what exactly is an active buffer? is it simple? becuase their cables have no electronics in them, and just a wall-wart... unless its tiny, they couldnt be doing this, unless they are doing it their master ac coupler... (a separate component that you plug the cables into)
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Old 11th February 2003, 07:04 PM   #4
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Just an impedance converter. High Zin, low Zout. Nothing but an op amp perhaps. May be very small, if you use an smd part.
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Old 11th February 2003, 07:08 PM   #5
cowanrg is offline cowanrg  United States
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forgive me, but i have very little to NO knowledge of electronics... i basically just know what certain parts are and generally what they do. is there anywhere i could look, or could anyone help me with a circuit? i would be very interested in building one of these.
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Old 30th January 2007, 03:42 PM   #6
mbl is offline mbl  Angola
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Anyone can post the schematic circuit and photo ?

Any reference for diy active shield cable and diy audioquest DBS cable?
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Old 30th January 2007, 07:55 PM   #7
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Buffering on cables is something that's also used for microphones where you have a really long stretch of wire to soak up signal and on oscilloscope probes where the signals are moving so quickly that just a foot of good wire will upset the measurements.

You can buffer cables using a FET alone. If you look up, FET Preamp on google you should come to a site a guy I've spoken to has written about a tiny FET amp you can build to put inside guitar cables.

If you take something like an opamp, there are two pins for you positive and negative power supply and two for the input and output.

The trick to buffering is that the output of the opamp can supply far more current than the input needs - you could think of a hydraulic jack opening the gate on a hydro power station, the jack only needs a litre or so of oil injecting into it to make billions of litres flow through the gate. The input of practically anything electronic used for measuring a voltage has a capacitance (a space that needs electrons to fill it up). When that voltage going in changes a bit, current needs injecting into or drawing from that tiny capacitance to make it represent the new voltage (take some electrons out of the bucket, the level goes down, put some in and it goes up). That's the drive current of the input. The output current comes from the power supply rails. So where as your original signal source might have been able to supply 2V at 0.1mA, the opamp might be able to output 2V at 10mA. Same signal voltage, but more current capacity. You can think of the voltage as the thing you're trying to represent and the current as how good the thing is at representing it. Cables have capacitance, like the input of the opamp, but substantially more (a swimming pool say). The opamp can help because it can push and pull current into and out of that cable capacitance to make the correct signal voltage appear across it, quickly (rather than adding electrons to the pool one at a time, the output of the opamp is like a garden hose). There are 20 chicks in your place and they want to have a bikini party right away, do you a.) fill the pool drop by drop, b.) use the hose? Now think about emptying and filling the pool ten billion times a second and you're in the world of GHz electronics.

I was mainly interested in valves when I started looking at audio electronics, but you can noodle around with opamps for a few $'s and have fun - it's great to hear your first correctly amplified signal coming out of an inaminate black blob on a DIY perfboard amp. And for very little more $'s, you can use seriously cool opamps.
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Old 7th April 2007, 01:23 PM   #8
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Default has anybody found something

by now..... i have just stumbled on this thread and i am also interested in the same subject but i can't make much out of the last reply from eeka chu......
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