[BlackCat]

I just saw and ordered this stuff at Parts Express...to cover my power cord in my DIY powerbox.  They claim it offers RFI shielding...and it looks WAY cool.

http://www.partsexpress.com/pe/showdetl.cfm?st=0&st2=0&st3=0&DID=7&Product_ID=119692&DS_ID=3

[JoshK]

This raises an interesting point, a question I have wanted to ask for some time now.  I see that some manufacturers build shielded IC's and power cords and some deliberately do not shield their cords/cables.  What are the pluses and minuses?

[Hantra]

Josh:

Shielding changes the electrical properties of the cable.  Capacitance increases with more shielding, and it will change the sound.  Manufacturers that do it obviously have weighed the benefits and decided that they outweigh the negative impacts of shielding.  

There are certain manufacturers that are not convinced that shielding, even on power cords, is necessary.  

HTH,


B

[BlackCat]

A good question Josh.  I got the stuff to provide RFI shielding, but only because in the original recipe for the powerbox, he used a 4 strand stove cord, the fourth strand being a simple copper braid, its construction within the cord being for the purpose of some sort of shielding.  I've seen this on a lot of other DIY power cord designs, like VenHaus, but he uses it on the outside.  The cord I got is a nice, flexible, rubber encased 3 strand 10 guage, nothing inside to provide any shielding.  I was going to put TechFlex on it anyway, that Flame Resistant black with subtle white stripes you see on a lot of powercords, but I came across the Chrome, and it seemed like a nice match with RFI shielding.  I'll have some time to do a little listening test before the Techflex arrives, so I'll see if I notice any difference.

[Ferdi]

HI, shielding is done on cables to keep stray fields in (power cable) or out (signal cable). Thinking about the configuration of shielded cables, I think the impedance of such cables is higher.

Only experimentation with different cables will tell you what combo works best.

Of course, it's the end of the day and I may be making this up.....

[audioengr]

This raises an interesting point, a question I have wanted to ask for some time now. I see that some manufacturers build shielded IC's and power cords and some deliberately do not shield their cords/cables. What are the pluses and minuses?

Hantra is correct, The capacitance increases significantly on shielded cables (5-20X), so usually a lot of detail is lost when you go shielded.  My own unsheilded cables are 3.8 pF/foot and the same thing shielded is over 10 pF/foot.  This is also tricky, because the best sounding shielded cables will generally be twin-axial (twisted pair in a shield).  In order to do this well, you have to make the shielding telescoping, or only connected at one end.  Otherwise, the impedance of the forward and return paths will be different, which is a bad thing, trust me.  Having the shield hang in the breeze has its problems as well - it creates an antenna for RF.

As for speaker cables and power cords, shielding makes no sense at all.  It only adds some capacitance, which might create a little low-pass filtering.  Easier to just add a capacitor.  It serves no useful purpose in these cases, technically.  The impedance of power systems and amp output is very low, so susceptibility is just not a concern.

[BlackCat]

You guys are forgetting...it looks cool!  Maybe audio is not all in the ears

[BlackCat]

Ok guys...humour me here, since I know nothing of the estoterics of electronics.  How can a metallized mylar wrapping on the outside of the rubber insulation effect anything on the inside of the powercord?  I'm not connecting the tech-flex to ground or anything like that, just using it on the outside, where even I could see that it might provide some shielding against RFI?