DIY dotcom wiring harness

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folpon
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DIY dotcom wiring harness

Post by folpon » Tue Feb 11, 2020 10:09 am

Hey, wigglers.

Maybe this is a dumb question, but here it is:

I'm building sort of a DIY 5u case based around some parts I had lying around. I am short two "wiring harness" cables -- the cables I'd use to plug in the final two modules I'd like to include in my case (a simple dotcom VCA and envelope).

Specifically, two of these guys:
Screen Shot 2020-02-11 at 7.03.12 AM.png
I don't really want to buy a full 20-cable wiring harness from dotcom just for two cables. So:

There's nothing wrong with me just wiring up some 6-pin MTA headers myself, right?
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bwhittington
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Re: DIY dotcom wiring harness

Post by bwhittington » Tue Feb 11, 2020 10:37 am

Nothing wrong with that at all. The only issue to consider with more modules on the same psu is the psu's amperage.

I have a bunch of stray Dotcom power cables from wiring harnesses I've taken apart. If you PM me your address (and aren't in a terrible hurry), I would be happy to send a couple to you. All you would need to do is make sure they are securely connected to the rest of the harness under the wire nuts.

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folpon
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Re: DIY dotcom wiring harness

Post by folpon » Tue Feb 11, 2020 10:53 am

Thank you, bwhittington.

This is a pretty small system I'm powering via a 1.6a Analog Craftsman power interface.
Screen Shot 2020-02-11 at 7.49.45 AM.png
Currently everything seems to work fine with all the modules pictured, other than the VCA++ and the second envelope generator.

Do you think I would have any issues after adding these modules? I would still be drawing under 1 amp with these modules, according to MG.

Advice greatly appreciated. :)
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croute
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Re: DIY dotcom wiring harness

Post by croute » Tue Feb 11, 2020 2:43 pm

Be carful!Mos lab work with +/- 12 volts ;)

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folpon
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Re: DIY dotcom wiring harness

Post by folpon » Tue Feb 11, 2020 2:45 pm

Yes! I have a special 12v busboard for the Mos-Lab modules. :)
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SynthBaron
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Re: DIY dotcom wiring harness

Post by SynthBaron » Tue Feb 11, 2020 3:41 pm

You need a special tool to punch down wire into those connectors, though. They make two different kinds, and the cheap one is just about worthless. You're much better off buying them from someone else pre-made than trying to do a few DIY.

https://www.te.com/usa-en/product-59803-1.html
https://www.te.com/usa-en/product-58579-1.html

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Re: DIY dotcom wiring harness

Post by croute » Wed Feb 12, 2020 4:15 am

You need a special tool to punch down wire into those connectors, though. They make two different kinds, and the cheap one is just about worthless. You're much better off buying them from someone else pre-made than trying to do a few DIY.
Or a simply little plate skewdriver is efficient for to punch the wires in the MTA,i did that for all my power connector(around 30)and all works perfectly 8-)

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Re: DIY dotcom wiring harness

Post by Flareless » Wed Feb 12, 2020 4:27 am

croute wrote:
Wed Feb 12, 2020 4:15 am
You need a special tool to punch down wire into those connectors, though. They make two different kinds, and the cheap one is just about worthless. You're much better off buying them from someone else pre-made than trying to do a few DIY.
Or a simply little plate skewdriver is efficient for to punch the wires in the MTA,i did that for all my power connector(around 30)and all works perfectly 8-)
Please be VERY careful if you do this for power connectors. The screwdriver can shear through some of the wire strands leaving you with a cable that will likely short after a period of use.

The proper punch-down tool is definitely recommended for power connectors. And as croute said... the cheap one is just about worthless.
Rich

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Re: DIY dotcom wiring harness

Post by KSS » Wed Feb 12, 2020 5:05 am

croute wrote:
Wed Feb 12, 2020 4:15 am
You need a special tool to punch down wire into those connectors, though. They make two different kinds, and the cheap one is just about worthless. You're much better off buying them from someone else pre-made than trying to do a few DIY.
Or a simply little plate skewdriver is efficient for to punch the wires in the MTA,i did that for all my power connector(around 30)and all works perfectly 8-)
Using a small screwdriver will be more effective and safe with MTA156 than MTA100.

The way to improve over even the cheap T-tool is to use a dremel cutoff disk to make a slot in the end of the screwdriver at about the 1/3 point across the end. When you look at the connector, and think about how an IDC connection is made, you can see that pushing down with a too wide screwdriver into the slot will widen it and lead to failure. The T-Tool attempts to fix this with a thin blade. But now you have a new problem. You're trying to get that tool on the topmost point of the insulation so that when you press downwards it slides into the connector's insulation displacement knife-edge slot without widening it. But it's like balancing on a barrel or floating log. The narrow blade goes this way or that, and can end up cutting the insulation, wire strands or both.

When you make the slotted screwdriver tool, the flat end of the screwdriver tip is much wider than the T-tool blade, and therefore is easy to use to apply pressure on the wire insulation. And the slot you cut in the end with the Dremel means you don't ding or widen the contact slot as you press the wires into place.

If at all possible, buy or borrow the handle and die(s) of the expensive tool; it really does make using this MTA system a joy. But in the absence of that, the slot-modified screwdriver is *far* better than the T-tool or soldering. If you're going to solder, change to another connector type instead.

A final point is that the MTA series connector color determines what size wire is appropriate. Be sure to use the correct gauge for the connectors you have!

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