DIY DC power cables

[Speedskater]

While the AWG along with some other parameters do have some affect on the loop inductance. It's the closeness of the opposite conductors that has the most effect. With low voltage DC supplies, thin insulation is good. We don't need 600V rated wires.

[Speedskater]

a]  Isn't a Canare Star-Quad cable already shielded?

 

b] Shield wire do you mean pig-tail at the ends of the shield?

Pig-tails should be as short as practical.

Wires are never shields.

 

c] The Henry Ott book  "Electromagnetic Compatibility Engineering" has entire chapters on cables and on shielding.

http://www.hottconsultants.com/book.html

[Speedskater]

OK, when I see Star-Quad, I only think of Star-Quad shielded mic & balanced interconnect cables.

But then I only look in the shielded cable section.

Anything else to me, is just 4 conductor cable.

[Speedskater]

Heck, almost any 4 conductor cable can be wired as a Star-Quad. The exception might be a 2 twisted pair cable, but it will work just as well.

 

Side note: 14AWG Romex® 3 wire plus ground, makes a nice 11AWG speaker cable, but it's stiff and ugly.

[Speedskater]

There are safety issues when working with AC power line systems. All the pieces and parts used , must be safety rated for the intended purpose and the person doing the work needs to have the necessary skill & knowledge to do the job safely.

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I see that John S. replayed while I was typing.

[Speedskater]

14 hours ago, R1200CL said:

 

.....................................

Edit

Just found this article that may be of interest for some of you. 

http://phmusic.co.uk/pharri5833/connections1.htm

When a paper has information about 'technical earth/ground' systems to Mother Earth, I worry about what other mis-understandings that it contains.  And while the paper has lots of good information, it adds confusion in other areas.

[Speedskater]

Remember that the cross-section area of the Safety Ground/Protective Earth needs to be the same or large than the total cross-section area of all the Hots or Neutrals.

[Speedskater]

I went back and read more of the Peter Harrison articles at PHM Consulting. It may not be so much errors but the need of a good copy editor and some is Overtaken By Events (OBE) in his later writing.

 

His British English writing style is a bit of a challenge.  I read a lot of stuff from the UK but his is a little bit different.

[Speedskater]

3 hours ago, R1200CL said:

Then you may like this one as well. 

Power and Grounding for Audio and Video Systems

A White Paper for the Real World – International Version

Two versions of the same excellent Jim Brown paper.

I'm always posting links to the about 50 Jim Brown papers and Power Points.

 

http://www.audiosystemsgroup.com/publish.htm

[Speedskater]

3 hours ago, R1200CL said:

And maybe this one:

http://www.tnt-audio.com/clinica/ground_force_zero_e.html

 

Mark Wheeler doesn't have a clue on how electricity works.

[Speedskater]

10 hours ago, Ralf11 said:

what is the inductance for a typical length of the StarQuad cable?

Mogami

Speaker cable 0.6 to 0.7 uH per meter

Microphone cable  0.4  uH per meter (0.12  uH per foot)

The mic cable has thinner insulation, so the conductors are closer together. The closer the conductors the less induction but more capacitance. Inductance and capacitance are opposite sides of the same coin. If one goes down, the other goes up. For a DC power cable, low inductance and high capacitance are good things.

[Speedskater]

Belden 1804A cable  would make a nice Star-Quad  XLR balanced interconnect cable for harsh EMI/RFI environments (like near theater lighting systems). Not something most hi-fi systems need.

But it's not a good choice for RCA unbalanced interconnects. Belden makes many good coax cables with heavy braided shields.

With it's small conductors it's a bad choice for a DC supply cable.

[Speedskater]

Sorry John, I'll stick with the writing of, Neil Muncy, Henry Ott, Bill Whitlock, Jim Brown and others. All write that coax is the way to go.

 

Henry Ott writes:

 

Unbalanced Interface Cables

.......................we can conclude that for the case of an unbalanced interface, the only property of the cable that has any significant effect on the common-impedance noise coupling is the shield resistance.

 

http://www.hottconsultants.com/pdf_files/Audio Interconnections.pdf

[Speedskater]

8 hours ago, JohnSwenson said:

I'm staying away from AC power cables. The shielding technique is universal, but whether it makes any difference on a AC mains cable I have no idea, I'm not going to make any guesses, and I'm probably not going to be doing any testing any time soon.

John S.

It would be a challenge to test shielded AC power cords, because the problem would be so situation specific. First you need a hi-fi component that is radiating interference via it's power cord, then you need a component that is sensitive to receiving interference via it's power cord. Include the lengths and placement/dress of each cord and you have an almost  unduplicatable situation.

[Speedskater]

There is a whole lot of science in making Cat5 (and up) cables. Belden is a leader in that science.

 

Lots of Belden Blogs on the subject. But you have to do some searching.

http://www.belden.com/blog/index.cfm

[Speedskater]

Help me out, where is the 'external wire' mod  that John S wrote about.

A wire in it's self can't be a shield, but it can connect a shield to something.

[Speedskater]

Now I'm very confused. A bulk cable's shield should have continuity from end-to-end. While running an external wire from connector to connector may well reduce low frequency Common Impedance Coupling noise, it won't do anything to EMI/RFI interference.

[Speedskater]

There are some situations where the XLR balanced interconnect shield is not connected at the receive end.

Situations like running the cable from one building to another. Where a lot of AC power current might flow  thru the shield.

In this case a hybrid connection is used. That's a small cap from the shield to connector.

I still don't get this external wire idea, unless it's about common impedance coupling.

[Speedskater]

The 6moons writers are all poets, artists or dreamers, so don't put much stock in anything technical that they write.

 

When things sound different that shouldn't sound different, you don't just jump to the conclusion the A is better than B. Sounding different is only the first step. You need to investigate why they sound different. It could be an uncontrolled variable or a situation specific problem.

[Speedskater]

Written by Curious or 6moons doesn't change the need for further investigation.

[Speedskater]

In XLR balanced analog interconnect systems:

a] No balanced input circuit needs a pin #1 connection. The pin #1 is the shield and is connected to the chassis (if connected) it's to reduce noise and interference.

b] Phantom powered microphones do require pin #1 be connected at both ends.

c] Battery powered outputs should have the shield connected at both ends.

d] If the shield is only connected at one end, it should be the output circuit end.

e] Rather than not connecting the shield at the input end, a hybrid connection should be used, The hybrid being a small high frequency capacitor.

f] It is better to connect the shield at both ends, unless there is a strong reason for not doing so. Like going from building to building.

[Speedskater]

What specs are good.

 

   For a power cable:

a] Large total conductor cross-section area.

b] High total capacitance.

 

  For a long XLR balanced analog interconnect cable.

a] Symmetry in construction.

b] Lower total capacitance is better.

c] Small total cross-section area is OK or better.

 

[Speedskater]

c] Small total cross-section area is OK or better.

 

It's OK because a large wire is not needed for an interconnect. Electrically the wires could be much smaller but then they could be fragile and break,

 

It's better because smaller wires mean a smaller, lighter less expensive cable.

Smaller wires have lower total capacitance which can be good when connected to some output stages.

 

[Speedskater]

/& what might be where "long" starts?

For unbalanced interconnects, it's well past 3 meters (10 feet).

Maybe a little longer if both components are plugged into the same AC wall outlet.

 

For balanced interconnects, it's as you approach 100 meters (300 feet).

 

* * * * * * * * * * * * * * * * * *

/& what rules apply to 'unbalanced' interconnects?

Good long unbalanced interconnects are coax cables with a heavy braided shield.

Where heavy is the equivalent of about 14AWG or 2mm sq.

[Speedskater]

13 hours ago, Em2016 said:

With John understandably and rightfully more preoccupied with building his new house, appreciate if the regular contributing tech guru's can help with this below query 

 

When doing the star quad configuration (e.g. for making balanced XLR interconnects) how important is it to maintain the natural twisting direction of the cable, for the half-inch at the ends that connect the XLR pins?

 

In other words, are the benefits of the star quad geometry un-done if you twist in the opposite direction to the natural twist direction of the conductors in the cable, in this final half-inch of each end of the cable? If so, why? @Superdad @Daudio @Speedskater

In harsh interference environments it can be important. Jim Brown the pro audio EMI/RFI expert has done some testing.  But most of us don't live at radio transmitters, so don't worry about it.