C7 Unpolarized Power Cord

[Yoder]

Google C7, and I get a lot of info on playing C7 chords in the blues and jazz inversions, but not much to help me with my power problem.

I would like to make a C7 unpolarized power cord, but am not 100% sure how to best go about it. Intuitively, it seems like it would be a simple build. Is it actually as easy as it seems, and is there really very little to worry about assuming the workmanship is good? Am I correct in assuming that I just solder the wire-1 to contact-1, and wire-2 to contact-2 on both ends? Also, if I wanted to shield the cable would it be safe to use the ground of the 3-prong plug for grounding the shield or is this considered unsafe/unacceptable for a unpolarized C7?

Thanks.

 

[Grainger49]

I'm unfamiliar with the C7 power cord thing.  Power cords, yes, but C7 I don't get.  Can you fill us in?

 

[Yoder]

My bad. It is actually an IEC power cord with a C& adapter.

Below is the adapter:

Here is an image similar to one that I would like to build:

 

[Grainger49]

I have seen these for sale at Mouser and other large house suppliers.  I don't know if I own anything that uses them, but couldn't be sure.

My SACD/CD/DVD player uses a non-grounded but polarized IEC plug and wire.  Odd not to have a ground on a piece of equipment I'm using for audio.

I wonder why Philips did that?

 

[Yoder]

It is the same type of power cord used on MacMini's. Rather odd that Apple would use one of these on not only the Mini, but the Mini Server as well. I just want to replace the piece of junk that my Mini uses.

 

[Koda]

I have ordered various items from Cryo Parts in the past, and they have been quick to respond.
The C7 type plugs are not too common as an aftermarket upgrade part, however Furutech makes a very nice one with gold or rhodium plating.
    K.

http://www.cryo-parts.com/index.php/furutech-c7-connector

 

[jrebman]

Yoder,

Yes, I have a PC for my mini made from a furutech C7, but the body was modified so that you can get the ethernet cable in the mini when the power cord is plugged in -- ethernet works much better when the computer has power ).  My cable was made by Pi Audio group, and was not cheap, but made a very substantial improvement to the mini's sound.  I think hubbel also makes a c7, and that too is a good improvement over the stockcable.  Also, have you tried flipping the power connector on the mini end?  That can change the sonic presentation somewhat too.

That said, there are a couple of folks playing withlinear DC supplies for the mini, and one of my friends heard a prototype of this and said it unbelievably good and takes the whole mac mini thing to a new plateau.  FWIW.

-- Jim

 

[Yoder]

Mucho gracias for the responses.

Regarding the network port...I use wireless so that is not an issue, but I am curious how the body was modified to accommodate the Furutech. I have an Airport Extreme router, and it has the best range I have ever experienced on a consumer router. The speed of the thing just smokes. The AE is on the top floor and I stream Netflix to a wireless computer on the 2nd floor that is on a diagonal of max distance from the AE and have never had issues, even when 4 different computers have been streaming simultaneously (an intentional test.)

The second party cords are a bit pricey, so I thought I would build my own. I was looking at the stock cord today and it just exudes the stench of "crap." It looks and feels more like a ribbon antenna than a power cord. Once I build my BH IEC power cord, I am going to try it on my iMac (it serves as a TV, DAW, audio playback, browsing, and limited development computer) and see if it makes much of a difference. The iMac power cord is a little better quality than the Mini, but not by much.

Here's a question: in building a C7 power cord do you think the gauge of the wire will matter? Just from looking and feeling the stock cord, my guess is that it is around 18-20 AWG. I just may track one down and dissect it to see what Apple is using.

 

[jrebman]

I think the basic idea with the furu connector is to leave the outer body off and cover the exposed parts with apiece of pvc pipe or something and then fix it in place somehow and then put some heavy duty, glue lined heat shrink over it.

For a mini, I'd think the basic bottlehead power cord recipe minus the ground run will work really nicely.  two twisted pais, twisted together and one wirefrom each pair connected together -- making sure one pair is tited clockwise and the other counter-clockwise.  20 gauge each conductor resulting in a 17 gauge aggregate gauge per leg.

Grainger, a c7 is also known as a "figure 8" connector, and your tv and/or dvd player probably has one on it.

-- Jim

 

[Grainger49]

I think you are right, the TV probably has one also.

 

[Laudanum]

My SACD/CD/DVD player uses a non-grounded but polarized IEC plug and wire.  Odd not to have a ground on a piece of equipment I'm using for audio.

I wonder why Philips did that?

I have a CD player as well that has an IEC input socket and uses an IEC connector and 3 wire grounded cord and plug, but the ground is lifted inside of the chassis.  The ground wire is actually there but it isnt connected inside the chassis, intentionally by the manufacturer.  I think it's the Dynaco CDV-1 (or 2, whatever was the less expensive one).  I think it also used a Philips transport.  As a side note, I have 3 tube CDP's, all relatively lower priced players, no high enders (Dynaco, AH Tjoeb 99 and the second Jolida (903 I think).   Come to think of it, I dont think the Jolida uses a 3 wire cable,  I think it uses a 2 wire removable polarized cable with a connector/socket like or similar to the type pictured.  And the Tjoeb (Marantz) has a captive 2 wire cord with polarized plug.  When I initially acquired the 3 players, in addition to scratching my head regarding why the Dynaco would bother with an IEC entry and a 3 wire cord just to lifting the ground internally,  I remember wondering why NONE of them used 3 wire cords with seperate ground.

 

[Grainger49]

If it has tubes, as I would expect a Dynaco product to, the chassis should be grounded for safety sake.  I don't think UL would approve otherwise.  I may be wrong.

 

[Laudanum]

You're probably right but ground from the iec entry was not grounded to chassis.  I dont remember if I remedied it or not, I bought it new what had to be 10 years ago or so. 

 

[Paul Joppa]

It's complicated.

UL requires that products be double insulated before they approve an ungrounded device. That means (as I understand it) that there is no single failure that would result in he chassis being connected to the wall socket. Understand I'm no safety engineer, just reporting what I remember having read.

If you have grounds, then you can get "ground-loop" hum. This happens when the grounds of different equipment is not exactly the same, or when the grounds and interconnects make a loop and there is an AC magnetic field present. Also, if you have grounds, then your equipment is probably unsafe unless your house wiring also is grounded. Correctly grounded, that is - zero tolerance for imperfect electricians. The liability alone could drive manufacturers to double-insulate everything.

Of course there are other ways for hum to introduce itself in ungrounded equipment, so it's no panacea. But you can see that there are reasons some gear might be ungrounded.

 

[Grainger49]

BTW, it is easy to test if the outlet is properly grounded, use a tester with lights that indicate proper or fault conditions.  The key is if your house's grounding rod is installed properly.  I salt and water mine once a year to insure that the rod has electrolytes.  Mine is not under the house eave.  If it were I would water more often.

 

[Laudanum]

You'd be surprised (or maybe not) to find out how many homes arent properly grounded, often due to broken ground clamps or those that have come loose.  Even broken ground wires/strands themselves.  Ive seem homes use the drop cable as ground back to CATV plant because of bad power co. grounds.  On our own plant, the interface between the ground cable and the ground rod with a standard clamp was problematic enough that we began using a special kit that allowed us to weld the ground wire to the rod.  And that in itself helped alot because we had thousands of buried copper rods out there grounding strand, power supplies, power inserters etc. 

 

[Grainger49]

You are right, I'm not surprised.  Salting my ground rod was a suggestion from one of the most experienced and intelligent EEs I have ever known.  He designed the power distribution for the four green field K-C mills I worked on.  At K-C we often had a "noise free grounding system" for sensitive equipment and a power grounding system.  Both connected to buried triads and bonded together at one point at ground, under ground actually.

Now that I work on a wiring crew for Habitat For Humanity I see ground rods being driven every week.  I wish the crew I work on had wired my house, there are four licensed electricians, maybe more, I don't have an accurate count.  This is a professional crew.

 

[HF9]

Surprised I didn't notice this thread until now. I'm currently in the process of building my own C7 power cord for an ST35 I'm building here: http://www.diyaudioblog.com/2011/06/customized-dynaco-st35-kit.html . I'm using a C8 connector made by Shurter as the power inlet that I fastened to some FR4 material.

For the cable, I chose to use three 16 gauge silver plated copper in teflon conductors and a grounded shield on the source side, even through only two conductors will be attached at the amp side. There are multiple layers of teflon tape insulating the braided wires and shield. On the amp side, I'm using a low-cost connector from a seller on that auction site: http://cgi.ebay.com/FIG8-C7-style-connector-solder-tags-/170169090572?pt=UK_Computing_CablesConnectors_RL&hash=item279ede420c#ht_1249wt_812

The connector above is made in Japan, and sold from the UK. I'm not sure if there's a U.S. source for it. If there was a slightly nicer $10 plug floating around somewhere, made by Hubbell or Marinco, I'd use that, but I'm not paying $45 for a Furutech C7, no way Jose!

Typically, a stock C7 power cord will have 18 gauge conductors. There is a PS Audio Jewel C7 that is 12 gauge and an Audioquest NRG C7 that's 16 gauge IIRC. These are both around $60-70 street price.

The cheapie C7 connector will accept 16 or 18 gauge wire and provides a nice tight connection.

 

[HF9]

Finally all done with my 16 gauge C7 power cord:

See all the build notes here: http://www.diyaudioblog.com/2011/07/custom-c7-power-cable.html

 

[Yoder]

Finally getting back on my feet, and shall throw the big question out. Here is what confuses me when it comes to the C7 unpolarized power cord. Assume that I am using my C7 cord for my MacMini. We plug the cord into the wall that has the grounding pin, and neutral and live blades. Assuming that I have built the cable properly, then how is it that I can flip the C7 end of the cable and plug it into the Mini without causing havoc? Granted, only the neutral and live are going in but it seems that if I flip it that so that I have a live and neutral configuration that this would have an adverse affect. Anyone know what is it that prevents things from frying in this scenario? Thanks.