Shielded Bottlehead Power Cord, With Pictures

[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.

 

[Grainger49]

In 1984 I installed a computer room and process data acquisition computer. an IBM Mainframe.  Things have changed since then.  

I do remember using the isolated "noise free" ground in that room  But nothing special about the power cabling.  I do not remember if there were any IEC power cords or if they were attached.

If there are any other questions about power cord grounding and shielding we should start another thread.  This has morphed beyond a construction thread. 

 

[Yoder]

I just finished a shielded C7 cable for my Mac mini. I used a Furutech plug and C7. I had to do some major mods to the C7, which meant stripping it down completely. The cable is basically the same as yours though i just used three pieces of 16 gauge wire. One of the pieces was used solely as a "filler." I did not braid or twist the wire, but just laid it down straight, wrapped it in teflon tape, and then pulled the tinned copper sleeving over it. I soldered a ground to the tinned copper and grounded it to the AC plug just as you did.

The C7 was the tough part. The first one I got was defective and so they sent me a new one. I was going to use some PVC pipe, but instead used a cap from a bottle of guitar polish. After stripping off the C7 parts, taking a Dremel to it, and protecting the bare pieces with heat shrink; I put a little bit of hot glue on it to keep things from moving. I then put the "Dunlop" cap on, filled it with hot glue, and added the heat shrink. It made a considerable difference in the sound and I was able to do it for about 40% of the costs of a manufactured cable using the same components...minus the "Dunlop" cap.

The C7 Cable

The Hardware

Modified C7

Source of the Cap

The cap before cutting a hole in the top

 

[Grainger49]

Nice work.  Is the Dunlop cap at the C7 end around the wires coming out of the C7? 

 

[Yoder]

Yup. The Dunlop carnauba wax is also great for polishing the BH bases.