Power cord length

0 Members and 1 Guest are viewing this topic. Read 3904 times.

Occam

Capacitance, Capacitance, Capacitance
« Reply #20 on: 29 Aug 2004, 06:35 am »
Quote from: John Casler
Equal lengths of cable and IC's are only important when a signal is present that could be affected by the timing difference between significant length differences.

So since power cords carry no signal, the lengths are not relevant to any "affect" due to their length....

John,

The timing differences between signal arrival for rather large length differences in interconnects and speaker cables are on the order of microseconds, at most. Rather, the differences are more likely attributable to LC charateristics of that signal connection, in concert with the source and load impedances, resulting in differing phase/frequency charateristics. This is specifically why using differing length interconnects between a passive attenuator and monoblocs is a really, really baaaad idea.

Capacitance in powercords, distributed in nature, for both line-to-neutral (a good thing) and line&neutral-to-ground (a bad thing in excess) have magnitudes that are directly proportional to their lengths.
In the case of twisted multipaired LtoN cords (Bob Crumps designs f'rinstance) a minimal length is reccomended so that distributed capacitace  can do that voodoo that they do so well, actually much like the currently popular tweak of a 'properly' rated Auricap across Line and Neutral. The result of SUBSTANTIALLY differing lengths of PCs feeding monoblocs would be a strong difference in the noisefloor, how black the blacks between the channels, as well as differing subjective perceptions.

In the case of PCs with, IMO,  excessive line&neutral-to-ground capacitance resulting from lack of spacing of the shield from the line and neutral conductors, the result is a surreal presentation, dependant upon the current draw. The Unicable 14ga shielded cable is an example of this. This cord is nominally equivalent to the 'bang for the buck' Volex 17604; but because the Unicable lacks the insulating cabling to space the shield away from the other conductors, its use on power amplifiers can only be described as 'sucks'. A 1' Unicable would suck substantially less than a 9'Unicable PC. If you think that isn't relevant, I'll simply point out that the original BelCanto EVO was provided with that PC, and that the criticisms leveled at it correlate exactly with other's subjective charaterizations of that (and other PCs with excessive...)  Unicable PC.
I once inadvertantly mixed a Unicable and a Volex on my poweramp monoblocs. It took me about 20 seconds to realize something was horriibly wrong.... and about a hour to figure it out and resolve my error.:?

Off topic:
I believe one of the reasons the Volex 17604/5 is such great bang for the buck, is that the cabling spaces the shield away from the other conductors, thereby minimizing line/neutral to ground capacitance.  This was not a design goal, merely fortuitous happenstance. The insulating cablling is there to provide physical resiliance against folks stepping on the cables, etc..., potentially leading to shorts. The better power cordage manufacturers also provide that insulating cabling on their non shielded versions as well.

FWIW

StevenACNJ

  • Full Member
  • Posts: 398
Power cord length
« Reply #21 on: 29 Aug 2004, 12:19 pm »
I have 10 VH Audio PC's in my HT system. They are all cryo treated and terminated with Furutech gold connectors. I also use Walker SST treatment.  

Couldnt be happier.

andyr

Re: Capacitance, Capacitance, Capacitance
« Reply #22 on: 31 Aug 2004, 04:20 am »
Quote from: Occam
John,

The timing differences between signal arrival for rather large length differences in interconnects and speaker cables are on the order of microseconds, at most. ...
Paul, hi ... you would appear to me to be just the fellow to answer a couple of PC questions I have - can you oblige (to a fellow AKSAphile!!):

1.  You were specifically talking about PCs with shields.  Why do people use shields on PCs?  Specifically, yes I can understand that having a shield over the 6' length of your PC stops RFI from getting into that final 6' length of power wire but, shirley, it ain't gonna remove whatever RFI has already got into the unshielded wires behind the wall socket?

2.  As I understand it, braiding PC wires helps to remove 'noise' from the wires - ie. this IS an "RFI-reducing" measure.  Is this correct or baloney?

3.  The TNT-Audio "Power Snake" uses three lengths of coax ... for "active", "neutral" and "earth" (European/Oz naming convention) and you braid the three wires - with the shields earthed at the wall socket end only.

If my point 2 *is* correct, how can the beneficial, "RFI-reducing" braiding still work with an earthed shield over each wire?   :?

Thanks, Paul,

Regards,

Andy

Occam

Re: Capacitance, Capacitance, Capacitance
« Reply #23 on: 31 Aug 2004, 06:03 am »
Andyr,

1. Your point is interesting ' if you've miles of unshielded cable leading to that last  6', why....", and its adjucnt, 'if you've miles of poor quality wire leading...'  I could make the argument that is really the FIRST 6 feet of the electrical ciruit, but in truth, I've no clue. I can only rely upon my own 'scientific' subjective evaluations, admittedly, by definition flawed. And no, its not going to remove whatever rfi has already entered. That should be addressed by whatever 'mains conditioning' you choose to implement. This can be as simple as an X2 capacitor accross the line for each mains circuit, to whatever level of complexity you desire.

2. Yes, braiding (or twisting) increase emi rejection and decrease radiation, and also increase capacitive coupling, which can be a good thing, or very bad; it depends on 'to what' and the magnitude of that capacitive coupling. While I view high line-to-neutral capacitane as a very good thing which actually does act to remove noise, others would argue the benefit of that architecture come fron low line-to-neutral inductance. I've never seen a mathematical derivation of different kinds of braiding's characteristics, but twisting, both pair and star-quad is fully characterized in the repetroir of singnal transmission technology. A non mathematical puff piece is here -
http://www.canare.com/catalog.html
go to 'cable', then 'starquad speaker cable', then 'Tech Note'
Personally, I think braiding is an evil joke played by Ray Kimber, who's PBJs and 4TCs started this travesty and I truly despise their characteristics.....I know, yes... it may well not be the architecture, but  a characteristic of the wire itself, the stereotype of the worst of 'teflon sound'. And the teflon/silver versions aren't all that bad. But others, who I respect, seem to like this braiding stuff. After my traumatic experiences with Kimber, I've religiously avoided braids. Its a phobia.

3. What you are describing is floating the shield at one end, an attempt to form a Farady Shield around the cord. I've not heard the cord, don't understand the rational for the braiding given the shielding, sorta understand the rational behing the shield approach. When I've floated the shield on the load end on the Asylum Cord, I can't say that I'm sure that I could detect the difference between that and connecting the shield at both ends.  I've nothing to form any real opinion.

andyr

Power cord length
« Reply #24 on: 31 Aug 2004, 07:06 am »
Thanks, Paul.  Much obliged.  Re 3. ... I couldn't understand the rational for braiding given the Faraday shield either ... that's why in my own implementation, I just stripped off the outer PVC jackets and braids so I just have three silky (with their dielectric), braided thick cores.

Regards,

Andy