Connundrum: Eurorack Power Cabling for Two SPecific Modules

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Zodanga
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Connundrum: Eurorack Power Cabling for Two SPecific Modules

Post by Zodanga » Fri Oct 17, 2014 10:17 am

Hello, all -- I'm here petitioning some wisdom.

I had a bunch of somewhat older Eurorack modules in Doepfer road cases. I bought a bunch of new skiffs, so I pulled all my modules out of the old cases and am trying to fit them into the new ones.

Two of my modules have me scratching my head -- the Doepfer A-156 Dual Quantizer and the Livewire Dual Bissell Generator. On these, does the red stripe go DOWN as usual? Neither of these modules mark the -12v side of the cable on the PCB (growl).

The Doepfer road cases use unshrouded connectors for power (another bad decision), so the cables plug in either way; my new [4ms] cases use shrouded female power connectors, and they will not let me plug these particular cables in red-stripe-down because of the way they are 'keyed.' By the way, I own other Livewire & Doepfer modules and none of those modules/cables have this problem.

My gut feeling is that the modules do indeed have -12v at the bottom but the cables were made incorrectly, and I never noticed it before because of the Doepfer unshrouded power connectors. But I don't want to fry these... it's been so long, I may have KNOWN these cables get plugged in upside down and forgotten. Also, assuming the cables ARE made backwards, does anyone sell replacements? I checked a few of my old haunts and no one seems to be selling replacement Eurorack power cables.

Please tell me which way these go only if you are sure! <g> I can guess on my own! Thanks so much in advance for any advice!

Zodanga
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Post by Zodanga » Thu Oct 23, 2014 12:33 pm

PS -- My other two Livewire modules have the red stripe at the bottom and are keyed properly, which brings me back to thinking the cable in this instance was just sloppily made.

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daverj
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Post by daverj » Thu Oct 23, 2014 1:38 pm

Never trust the key on a ribbon cable blindly. Doepfer does not pay attention to the key when making the ribbons, and neither do a number of other manufacturers. Figure out which end of the connector on the module is the -12v and follow the ribbon from that point to the other end. Then decide for yourself based on that how to plug it in. If your power distro is keyed, then you might have to replace the cable or cut off the key if the cable is not keyed correctly.

Doepfer modules that have the power header on the module facing up and down are always oriented with -12 at the bottom. The one photo I found on the web of the Bissell from the back also shows the -12 at the bottom.

Zodanga
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Post by Zodanga » Thu Oct 23, 2014 2:12 pm

Thanks!

Yeah, I don't trust the key or the stripe, but the PCB is not marked on my Rev of the module... I guess I will have to take a chance that the negative rail is down on that Bissell. I _presumed_ the Doepfer module is -12v at the bottom but you never know.

I don't know what possessed DD to design an un-keyed power cabling system.

I'll just order a couple of new cables rather than do surgery... they're only about $3 each, I see.

Thanks again!

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ersatzplanet
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Post by ersatzplanet » Thu Oct 23, 2014 4:56 pm

I hate to throw in another "almost always" into the mix but here goes. MOST modules DO NOT use the CV and Gate busses. These pins on the 16-pin header are on the opposite end of the header from the -12V. The Pins go like this:

-12V
Ground
Ground
Ground
+12V
+5V
CV bus
Gate bus

If your module has a 16-pin connector on it, and no legend on it, look for the cluster of Ground connections. ALMOST every maker will either connect them to the ground plane or connect them all together. This can tell you which end the -12v is on. If the module maker is using a 10-pin connector on the module end then this is a different story and less easy to figure out.

Another "almost always" situation is the use of pin-1 of the header as one of the 2 pins used as -12v. TYPICALLY this pin's pad will be different than the others. MOST BUT NOT ALL, PCB layout programs will have pin one as a square pad and the others as round ones. The guy who laid out the PCB MAY NOT have kept this the same though.

You can trace the end pins back to the nearest IC and figure the power out from that but sometimes that is not easy to do.

Basically you look for ALL of these options and make a decision based on that. As daverj says - DON'T rely on the keys on the connectors. Follow the traces.
-James

James Husted - Synthwerks, LLC - www.synthwerks.com - info@synthwerks.com - james@synthwerks.com
Synthwerks is a proud member of the Mostly Modular Trade Association (http://www.mostlymodular.com).
Always looking to trade for Doepfer P6 cases

Zodanga
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Post by Zodanga » Mon Oct 27, 2014 12:41 pm

Those are great tips, thank you!!

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bandenoire
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Post by bandenoire » Wed Dec 31, 2014 6:04 pm

I'm running into the same problem with a Livewire AFG. Do they make adapters to swap the orientation of the cable?

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