Shielded Bottlehead Power Cord, With Pictures

[Grainger49]

Alex,

No, I followed the aftermarket one I already had.  I might try it with another power cord.

If the shield is grounded say at an Eros then the path to ground for any noise is through the shield, to the Eros chassis back through the power cord ground wire under the shield to the ground lug at the plug end.  It seems both circuitous and it ends shunting the noise into the power cord.  Where as if you ground the shield to the plug end ground lug it never gets into the conductors in the power cord.

Hmmmmm.... I'm going to have to think on this one.  

[ALEXZ]

Probably it is right way to ground at source.
Hovever, here is an alternative theory: star ground, where all grounded in one point on the chassis and from that point single wire goes to earth ground.  Well...  could be a pure fantasy, but I guess it's fun to try.

[Noskipallwd]

The cord I built for the Eros, I connected the shield to the source ground as I do with all the PCs I have built. The Eros is quiet, so at least I know it is not adding any noise. As to whether it helps remove noise, don't know.

Cheers,
Shawn

[Yoder]

did you try to compare shield groundig at source with grounding at receiving side ?

I have read in several different sources that you always want to ground at the source and never at the receiving end. There were some sound (no pun intended) rationalizations, but to be honest I just memorized the concept and not the science behind it.

[Grainger49]

Are we all saying that the wall is the source for the 120V AC, right?

[Yoder]

Yup.

[STURMJ]

IIRC, grounding the shield at both ends causes the shield to act as a antenna, introducing (potentially) more noise.

[Grainger49]

Yup, on that too!  You have a ground from end to end of the power cord, the green wire (or black in the case of the Bottlehead power cord).  The shield isn't supposed to be redundant to this wire.

[ALEXZ]

When we have shielded interconnect, we protecting signal going through this interconnect from outside world, correct ?
When we are shielding power cord, what are we protecting ?   Power wires from receiving radio signals, or we are protecting surrounding equipment and interconnects from this power cable ?

[Yoder]

When we have shielded interconnect, we protecting signal going through this interconnect from outside world, correct ?
When we are shielding power cord, what are we protecting ?   Power wires from receiving radio signals, or we are protecting surrounding equipment and interconnects from this power cable ?

I use shielding to protect the cord/cable from EMI and RFI. I would guess that it can work both ways.

[Paul Joppa]

I would imagine that if there is already radio-frequency noise on the house wiring, that it would couple capacitively to the shield and drain to ground. Just a guess, I've done no calculations or measurements!

[ALEXZ]

I use shielding to protect the cord/cable from EMI and RFI. I would guess that it can work both ways.

How about hundred meters of power cable running from transformer to the outlet  - is it shielded ?
Power cord supposed to transfer 50/60 HZ  relatively high current  and ends with the primary of power transformer. Capacitor across power line will kill EMI / RFI. I doubt you have the same requirements to shield power cord loaded by  hundred ohm or less on one side and whatever is secondary impedance of the distribution transformer  on the other, and your turntable cable loaded by 47k on one side  and  cartridge on the other and running 3mv ( MM cartridge).

[Grainger49]

With a coaxial interconnect with a center conductor and a single shield, the shield is falsely assumed to keep out RF.  The signal goes through that shield which is tied to the common at both ends.

Some interconnects have double shields.  The inner shield carries the signal and the outer is grounded at the source end only.  This can also be done with a twisted shielded pair (TSP), as in all  Bottlehead equipment that uses TSP.  The outer shield gives an added measure of protection from noise.

I am thinking that a shielded power cord is supposedly protecting the inner conductors from magnetic and RFI/EMI.

[Grainger49]

I use shielding to protect the cord/cable from EMI and RFI. I would guess that it can work both ways.

How about hundred meters of power cable running from transformer to the outlet  - is it shielded ?
Power cord supposed to transfer 50/60 HZ  relatively high current  and ends with the primary of power transformer. Capacitor across power line will kill EMI / RFI. I doubt you have the same requirements to shield power cord loaded by  hundred ohm or less on one side and whatever is secondary impedance of the distribution transformer  on the other, and your turntable cable loaded by 47k on one side  and  cartridge on the other and running 3mv ( MM cartridge).

I have installed a lot of power cable from 5kV down.  I don't remember any of it being shielded.  But this was an industrial application.  Sensitive electronics were protected in many other ways, not the subject of my thread.

[ALEXZ]

Interestenly,  in dataceners often power cables that comes with the core equipment (switches, blades chassis etc.) are shielded. The reason is to protect data cables from noise transmitted by switched power supplies via power cables. Those cables, I believe,  have shield connected on both sides.  BTW, 240v cable with twist'n'lock industrial connector one one side and IEC  C19 /C21 from vendors like  Cisco, IBM, EMC costs at list few hundred dollars.