Ultra Low Mass Interconnects and Connectors

[Steve Eddy]

For the life of me I've never understood why those who routinely DIY continue to use RCA connectors. I can see keeping the RCA connectors on commercial equipment (voiding warranty, resale value, etc.) but when it comes to the one-off stuff we make for ourselves, why would anyone want to use sow's ears like RCAs (which in my opinion not even Eichmann and WBT can make into silk purses) when we can use anything we want?

Anyway, I thought I'd offer up one alternative that's ultra simple, ultra low mass and can be easily incorporated using simple perf board.

I'm talking about 0.025" square pin headers and sockets (anyone who's set jumpers on a computer motherboard or peripheral card know what these are).

While the constituent parts are readily available and inexpensive, this isn't exactly a cheapskate approach as I wouldn't even recommend thinking about it without using the proper crimping tool for the sockets which can cost close to $200.

On the bright side however, the pins and sockets can be used for other purposes such as prototyping.

To begin, I wouldn't have even considered this approach for intreconnects if the sockets weren't available in special high contact pressure versions which is what you'll want to use for this if you choose to give it a try. For just two contacts, the normal sockets just don't have much of a grip and can slip off rather too easily.

So on with the show.

I started out with a quad braid of 30 gauge solid core wire. For this I used my own silk insulated wire but the same can be done with magnet wire, wirewrap wire or other insulated 30 gauge solid core wire.



Next unbraid about 2 inches of the cable and twist the pairs together, leaving half an inch or so untwisted.

The quad braid is essentially two interwoven twisted pairs with each twisted pair offset 90 degrees from the other. To make wire pairs I use one wire from one twisted pair and one wire from the other. The remaining pair is made up of well, the remaining pair.



Strip (or tin in the case of magnet wire) the untwisted half inch of wire, line them up parallel and cover the twisted portions with heatshrink.

By the way, the photos aren't the greatest and what looks like silver on the bare wires is just light reflecting off the wire.



Next trim the bare wires so there's just 1/8" extending from the heatshrink (the heatshirnk by the way is to provide strain releif and give the insulation portion of the sockets something to dig into).



Next crimp on the sockets, keeping the two sockets lined up so neither has to be twisted to get it to line up with the square pin header.



Next slide some slightly larger heatshrink over the sockets and long enough so that it covers the crimped portion as well as a bit of the heatshrink previously applied.



You could choose to leave the cable "nude" however I chose to put a braided cotton jacket over this. To me it doesn't negatively affect the sound in any way and it gives the cable a much better "feel."



Then some heatshrink over the cotton jacket.



Now, the other half of the connector, the pin header.



And finally, contact.



Enjoy.

se

[sx881663]

Steve,
You are thinking and I like that! While you are experimenting with this try completely covering the exposed ends of the pins, use 2 or 3 layers and make the outer layer of one of the pins red for polarity. Then at this point do an overall clear jacket while the pins are secured to a header strip. This will form a useful plug. If you have built the layers up enough and use enough heat you will be surprised at how well it will work just don't move it till it is completely cooled down.
There are much cheaper crimpers that will do an adequate job as long as you don't plan on doing hundreds of them.
How about a vendor link for the high quality pins?
Next is all the wire experiments that can now be easily done. I would recommend you try a single twisted pair of 24 ga Kynar computer wire as a possibility. You might even try magnet wire.
Roger

[Steve Eddy]

Originally posted by sx881663
You are thinking and I like that! While you are experimenting with this try completely covering the exposed ends of the pins, use 2 or 3 layers and make the outer layer of one of the pins red for polarity. Then at this point do an overall clear jacket while the pins are secured to a header strip. This will form a useful plug. If you have built the layers up enough and use enough heat you will be surprised at how well it will work just don't move it till it is completely cooled down.

Yeah. I didn't have any other colors on hand so I just went with the black figuring that some sort of polarity indication would be obvious.

Don't know that I'd go with all the extra heatshrink though. It's not terribly difficult to just hold the two connectors side-by-side and plug them in. If one's really afraid of shorting, perhaps some heatshrinking over the ends or just use a two socket housing that's made for the ones you're using.

There are much cheaper crimpers that will do an adequate job as long as you don't plan on doing hundreds of them.

If you're aware of one, I'd like to see it.

How about a vendor link for the high quality pins?

Pins or sockets? The sockets I used for the photos were some Molex types that I had on hand. The ones I'd recommend (which I ran out of a few months ago and haven't got 'round to reordering) are the AMP AMPMODU V high pressure sockets.

AMP part number for the 32-27 gauge sockets is 103455-2 which can be had from Mouser as part number 571-1034552. Mouser also sells the AMPMODU single row breakaway headers in a variety of lengths and plating options.

Next is all the wire experiments that can now be easily done. I would recommend you try a single twisted pair of 24 ga Kynar computer wire as a possibility. You might even try magnet wire.

Been there, done that. Spent a couple years finding out what worked best for me. I'll leave it to others to experiement and find out what works best for them.

se

[Steve Eddy]

By the way, I didn't like that funky discontinuity in the outer heatshrink due to the second heatshrink over the sockets not fully covering the first heatshrink so I made one that did. Aesthetics isn't everything, but it ain't exactly nothing either.



se

[zobsky]

timely post , ... i was busy contemplating why WBT connectors must cost $$$ when i saw this.

... what's the advantage of this as opposed to RCA plugs / sockets (apart from the cost of the materials) ?


regards

[Steve Eddy]

Originally posted by zobsky
timely post , ... i was busy contemplating why WBT connectors must cost $$$ when i saw this.

Well, there's a simple answer to that. It's because there are a sufficient number of people willing to pay what WBT is asking. Good ol' market pricing.

Of course part of it is also the fact that WBT doesn't have the economy of scale that would keep unit pricing down.

... what's the advantage of this as opposed to RCA plugs / sockets (apart from the cost of the materials) ?

Part of it is personal. I just don't like RCA plugs and sockets. They're a coaxial connector designed and intended to be used with coaxial cable, which I also don't like. At least not for audio. And I just find them a very inelegant solutoin for terminating non-coaxial, multi-conductor cable.

XLRs are more in keeping with terminating multi-conductor cable but I don't like XLRs either because they're just so hideously large for what they have to do. I mean, the quad braid cable I used for this piece, I can literally fit four of them (cables, not conductors) in the solder cup of a single XLR pin.

I once terminated some of that cable with XLRs and it looked like two plumb bobs on a string. Bleah.

Another reason is that I like eliminating superfluous material and this approach keeps superfluous material to a bare minimum.

And finally, I simply think they sound great.

se

[sx881663]

Originally posted by Steve Eddy


Yeah. I didn't have any other colors on hand so I just went with the black figuring that some sort of polarity indication would be obvious.

Don't know that I'd go with all the extra heatshrink though. It's not terribly difficult to just hold the two connectors side-by-side and plug them in. If one's really afraid of shorting, perhaps some heatshrinking over the ends or just use a two socket housing that's made for the ones you're using.



If you're aware of one, I'd like to see it.



Pins or sockets? The sockets I used for the photos were some Molex types that I had on hand. The ones I'd recommend (which I ran out of a few months ago and haven't got 'round to reordering) are the AMP AMPMODU V high pressure sockets.

AMP part number for the 32-27 gauge sockets is 103455-2 which can be had from Mouser as part number 571-1034552. Mouser also sells the AMPMODU single row breakaway headers in a variety of lengths and plating options.



Been there, done that. Spent a couple years finding out what worked best for me. I'll leave it to others to experiement and find out what works best for them.

se

Thanks for the “socket" info.
Here are 2 much cheaper crimpers that should work well enough, especially with a follow up solder job.
http://www.allelectronics.com/cgi-bi...T-1&type=store
http://www.mouser.com//catalog/specsheets/105194.pdf
Your redo looks much better but the pins still need to be covered to the end to prevent eventual oxidation. This will also increase the holding force as well.
BTW, like your camera work. What do you use?
Roger

[Steve Eddy]

Originally posted by sx881663
Thanks for the “socket" info.

You're welcome.

Here are 2 much cheaper crimpers that should work well enough, especially with a follow up solder job.

I have a set of those. They don't work well at all for these sockets. They just make a mess of them. If you're not going to use the right crimping tool, then I wouldn't bother crimping at all and just use solder.

Your redo looks much better but the pins still need to be covered to the end to prevent eventual oxidation. This will also increase the holding force as well.

Thanks.

The sockets I recommended though have gold over nickel so there's nothing to oxidize. Though increasing the holding force a bit won't hurt.

BTW, like your camera work. What do you use?
Roger

Thanks. I'm using an old Nikon CoolPix 990.

se

[BobEllis]

thanks for this idea, Steve.

Now for the silly question: where do you get the braid? I couldn't find it at McMaster's website, my usual spot for odd things.

Thanks

[Steve Eddy]

Originally posted by BobEllis
Now for the silly question: where do you get the braid? I couldn't find it at McMaster's website, my usual spot for odd things.

Oh, I have elves that come in at night while I'm sleeping and make it up for me.

I do the braiding myself. Here's a guide on how to do it yourself:

Four Strand Braiding Illustrated

Be sure to read my correction post just below it.

se