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Old 15th April 2003, 09:20 PM   #31
jcarr is offline jcarr  United States
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Carlmart:

Demian Martin has a patent on a DC biased-shield cable. One of Demian's principle goals was to bias the dielectric so that it never changed polarity.

Patent link:

http://patft.uspto.gov/netacgi/nph-P...S=PN/5,307,416

Bootstrapped (driven) shielding is occasionally discussed in opamp and buffer amp data sheets and application notes, and these can be seen in the data sheets from IC manufacturers such as TI

http://www.scanti.ru/docs/datasheets/sbos003.pdf , Figure 13,

and National Semiconductor

http://www.national.com/ds/LH/LH0033.pdf , page 10.

hth, jonathan carr
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Old 15th April 2003, 10:51 PM   #32
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Default DRIVING THE SHIELD.

Hi,

Quote:
One of Demian's principle goals was to bias the dielectric so that it never changed polarity.
Yes, and I can show work of L'Audiophile for which magazine I contributed for a number of years that explained these principles well before this got patented...our mistake.

The active cable driver does more than that however but unless you need to deal with severe impedance mismatches between sender and receiver I feel it's rather superfluous.

The idea behind it is to treat the interlink as a transmissionline, I've explained my thoughts about that in the " Blind Listening test" thread at great length and have been told a few times that this shouldn't be an issue at audio frequencies.

I disagree, it does and here is one reason why cables do sound different: diferent transmission line will give you different sound, all else being kept equal.

Cheers,
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Old 16th April 2003, 02:22 PM   #33
jcarr is offline jcarr  United States
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Hi Frank:

Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case.

Regarding the rest of your post, I do use bootstrapped shielding on occasion, but my main reason is not impedance matching, but rather to null out load capacitances.

regards, jonathan carr
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Old 16th April 2003, 06:01 PM   #34
PMA is offline PMA  Europe
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Hi jcarr,

all of those methods work. 1) Impedance matching at the beginning and end of the cable,
2) Nulling of the load capacitance,
3) Transfer of the current to the summing point of the opamp (virtual ground).

Pavel
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Old 16th April 2003, 09:57 PM   #35
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Default Patent

"Don't worry about the patent. I don't think that Demian has enough money to successfully prosecute any infringement case. "

I am waiting for them to sue manfactures of phantom powered microphones. I did sell an AES/EBU digital cable with a biased shield that sounded very good. There was actually an optimum bias voltage for the cable. It used a topology outside the scope of the patent. One could drive the shield with an amplifier with a DC offset to acheive both the usual objectives for an "active shield" type cable.

Many metalized film caps also sound better with a bias voltage, even on a SPDIF digital interface. It maybe that the electrostactic force creates a more stable capacitance value from the plates not moving as much with signal. This is about ten year old technology for the audio tweakers by the way.
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Old 16th April 2003, 10:31 PM   #36
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Default Re: DRIVING THE SHIELD.

Quote:
Originally posted by fdegrove
Hi,



Yes, and I can show work of L'Audiophile for which magazine I contributed for a number of years that explained these principles well before this got patented...our mistake.

The active cable driver does more than that however but unless you need to deal with severe impedance mismatches between sender and receiver I feel it's rather superfluous.

The idea behind it is to treat the interlink as a transmissionline, I've explained my thoughts about that in the " Blind Listening test" thread at great length and have been told a few times that this shouldn't be an issue at audio frequencies.

I disagree, it does and here is one reason why cables do sound different: diferent transmission line will give you different sound, all else being kept equal.

Cheers,
Cable impedance is not usually an issue at audio frequencies but is a real factor at FR frequencies. Source termination of the cable driver is one approach and terminating the cable with its characteristic impedance is another. I use an RC load termination for the cable at high frequencies without having to drive 50 to 100 ohms at audio frequencies. This also filters RF out of the input to the amplifier. The load of a cable can have a serious effect on the phase margin of the circuit driving the cable. Many people fell that the best bass response and dynamics are achieved by diving cables with a very low impedance. RC load termination has an advantage over source termination in this respect.

http://www.intersil.com/data/elantec/d40954.pdf

http://www.analog.com/UploadedFiles/...34159AN257.pdf

http://www.analog.com/UploadedFiles/.../362551532.pdf ( page 12)
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Old 16th April 2003, 10:35 PM   #37
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Default Hey Phred..........

Are you going to tell us who that scumbag stole the idea from in the first place???????

Along with no money, we can also assume lots of other things he lacks...........

Jocko
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Old 17th April 2003, 01:09 AM   #38
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Default HYPERACTIVE.

Hi,

Jonathan,

Quote:
Regarding the rest of your post, I do use bootstrapped shielding on occasion, but my main reason is not impedance matching, but rather to null out load capacitances.
Same here...not much new under the sun lately it seems.
I find it very useful on shielded speaker cables in particular.

Fred, Jocko and a pizza,

Quote:
The load of a cable can have a serious effect on the phase margin of the circuit driving the cable. Many people fell that the best bass response and dynamics are achieved by diving cables with a very low impedance. RC load termination has an advantage over source termination in this respect.
I couldn't agree more....Now how do we transmit this to the rest of the fraternity?
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