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dorkus 19th June 2002 08:00 AM

"cable chargers" - DC biasing cables?
(this message is also posted in the Son of Dork Active Circuitry thread...)

i vaguely remember a while back, there was a product called a "cable charger" which DC-biased interconnects on one end, and AC-coupled them at the other with a high-quality film cap. supposedly this was supposed to optimize the signal transmission to some degree, though it was never explained to me how it did so. the editor of my audio magazine said despite the added coloration of the capacitor, he felt it often made a worthwhile improvement in sound quality.

i was just thinking about this in connection with my "Son of Dork" preamp... just random thoughts of the Borbely SE circuit, high-pass filtering my main speakers (i have a subwoofer), connecting the preamp to my amp, and dielectric performance. it occured to me that all cables are capacitors to some degree, and most any capacitor seems to perform better when DC biased so as to avoid signal zero-crossing. maybe this "cable charging" stabilizes the dielectric and avoids any nasties that might be associated with zero crossing? there was also some claimed supression of RF interference, though i have no idea how that would work.

so i have an idea for Son of Dork... why not combine the best of every world? i could use the Borbely SE circuit, which has an output offset somewhere around +12V or +15V depending on supply. then, i would have a special DC-coupled output on the preamp that has no coupling cap - just the straight SE output, DC bias and all. i would run this signal through the interconnect to the amplifier, then have in-line RCA/XLR adapters at the amplifier end with blocking caps in them. i could even select the value of the cap to deliberately high-pass filter the signal where desired, say at 60Hz for my main speakers.

using such a scheme, i could use a SE preamp circuit that everyone seems to favor, get the benefits of cable DC biasing, optionally high-pass filter my mains, and still have only one capacitor total in the signal path. the only catch is that i'll have to be VERY careful to label the DC-coupled output of the amp as such, and only use this output in conjunction with the blocking caps at the other end - otherwise i could fry my speakers in an instant. i might consider even using a different type of terminal (BNC or something) to prevent such an accident.



tiroth 19th June 2002 01:54 PM

If you are using balanced interconnects you can also get some free bias removal as long as bias+signal is in the common mode range of your reciever.

mrfeedback 19th June 2002 01:55 PM

Cable Bias
Hi Dorkus, I think Harry or Jocko mumbled something about Dc polarising of interconnects, maybe digital ones.
What about a power amp stage that requires DC bias on its input to maintain output DC balance ?
No series caps needed at all.

Regards, Eric.

Peter Daniel 19th June 2002 02:46 PM

To me it sounds like an interesting idea. I started a thread on that subject a while back:

tvi 19th June 2002 02:57 PM

The patent is here:
<a href="'5307416'.WKU.&OS=PN/5307416&RS=PN/5307416">US Patent 5,307,416
Martin; Demian T,
Bias circuit for cable interconnects</a>


nar 19th June 2002 03:14 PM

Yeap.Sounds very cool to me.Any result for this soundquest research ? Nelson?...Any idea about this?...Sure you read the thread...

dorkus 19th June 2002 03:48 PM

ahhh, that's right. Demian Martin, i recall the name now. i should ask my editor what happened to the product, i haven't heard anything about it lately.

p.s. HPotter, i just read your original post, i must have missed it in my search. eerily similar to mine! :)

Jocko Homo 19th June 2002 05:25 PM

Demian Martin......a prime example of why I think the Patent Office should be closed. Or at least fixed.


dorkus 19th June 2002 05:31 PM

jocko, i hate to admit it but i'd have to agree with you. did you hear the story how one small internet advertising company is trying to patent the "pop-under" ad? which, for those who don't know, is just a couple of lines of javascript. they actually think they can charge a royalty to every person using it.

tiroth 19th June 2002 05:34 PM

What about Amazon's successful one-click patent? Not exactly a revolutionary idea.

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