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July 18, 2011

Custom C7 Power Cable

If you're familiar with a standard IEC inlet, it has three separate connectors for hot, neutral and ground and is on nearly all audio equipment worth its salt, with a few exceptions of course. But we just can't be lucky enough that all equipment has an IEC three prong power inlet, can we?

Furutech gold IEC power inlet
Older equipment and certain newer universal disc players, among other things, have a C7 inlet. A C7 inlet does away with the safety ground connector, and is unpolarized, meaning that the hot and neutral is interchangeable as the cord can be aligned either way on the inlet. There are certain C7 connectors that are polarized which have a square end on one side and a circle on the other to ensure the hot and neutral go through the appropriate route.

Polarized C7 power cord
In my case, I'm currently building a Dynaco ST35 kit which combines the circuit ground with the chassis ground. When this is the case, there is a good chance for hum if attaching a preamp and amp on the same breaker if the circuit ground of each is attached to the safety ground of the power cords. Many of the forums I've visited recommend not attaching the chassis ground to the safety ground on the power connector to prevent hum on Dynacos. Please note that safety ground is called safety for a reason, if it's not connected and the circuit shorts to the chassis, it can be very unsafe.

I'm using a Shurter C7 inlet for my ST35, and it would be blasphemous for me to connect an ordinary C7 power cord to my tricked out new Dynaco ;)

Schurter C7 Power Inlet
So, what are the options for aftermarket C7 cables? PS Audio produces the 12 gauge Jewel power cord which is offered in a C7 configuration and runs ~$70-80 on the street, then there is the Audioquest NRG-1 power cord, which has a similar street price and comes in 16 gauge. Both are larger than the typical 18 gauge unshielded C7 power cord that comes with most equipment and are of course much more attractive.

In the interest of DIY, I chose to build my own. There are sparse few choices for a cable-end plug. Furutech offers a very attractive one, but at $45 as of this writing for a C7 plug is a little rich for my blood ;) It's also a little large for my purposes.

Furutech C7 power plug
Luckily, a builder in Japan offers a low cost C7 connector with solder connections that accept anything up to 16 gauge. These are floating around on that auction site if one searches for "C7 solder".

The power cord starts off a little differently than my other power cords. Rather than twist 10 gauge wires together in a spiral, I chose to use 16 gauge wire and braid it in a tri-braid configuration.

A bundle of 16 gauge silver plated copper in Teflon

Tribraided conductors
Then came the Teflon tape insulation, which covers the braided cable twice over.

Initial Teflon wrapping
A shield is then added over the top, which is connected to the source side ground via a soldered bus wire to create a floating shield.

Wrapped with a tinned copper mesh shield
The next step is two additional layers of Teflon are added to the top, over the braided mesh shielding.

Teflon wrapped 16 gauge power cord
Finally, the decorative techflex sleeving is added to the top, in this case both Chrome XC and black PET sleeving was employed to give a low-level shimmer. The low-cost Marinco 5266 is screwed down on one end and the C7 connector is soldered to the other. A piece of heatshrink is used as a strain relief, and in this case, the joint was bent at 90 degrees while the heatshrink was still hot for ample clearance behind the amp.

High quality DIY C7 power cord

Reverse shot detailing Techflex covering


The Fine Print:
The above steps detailing the creation of a power cord are for entertainment purposes only, and not to be performed under any circumstances. Please remember that attempting to use homemade power cords can be dangerous to you and/or your surroundings. The owner of this blog and all associated parties can not / will not be held responsible if you attempt the process posted below and cause physical harm to yourself or your surroundings. Many electronics contain high voltages that can kill, and DIY power cables can be a fire hazard. Please keep this in mind.


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