12V Trigger Cable - 2.5mm/3.5mm Mono Plug to Bus Block

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edited May 2016 in DIY, Mods & Tweaks
12V TRIGGER CABLE - 2.5mm/3.5mm MONO PLUG TO BUS BLOCK
For the past couple of years, I've avoided the 12V Trigger option for powering on an amp after turning on the preamp if it wasn't available as a plug and play option by using a 3.5mm mono cable. At least some of the Parasound gear uses the 2.5mm cables, which I never had on hand and always meant to order, but never got around to. Further, their earlier amplifiers use a bus block for the 12V connection, something that always made me a little nervous, never really knowing what's what, and thinking I'd somehow burn my house down if I messed it up. Some B&K stuff does this, as well.

TRIGGER BUS BLOCKS
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Instead of messing with preamp/amp direct triggering at the time, I opted for use of the triggered outlets on the refurbished Panamax M5300-PM power centers I picked up a couple of years ago. In this case, you simply connect your pre/pro to one of the Always On sockets, and wire that equipment's 12V trigger Out to the 12V trigger In on the Panamax. Then, when you turn on the pre/pro, this triggers all six of the switched outlets on the M5300. It works pretty well for turning on or off several components automatically, but it only has two switched high current outlets. This would probably be fine for most common use, but can be a drawback if you've got more than two pieces of high current equipment, like amplifiers, or are testing a bunch of stuff, and can't easily access the back of the unit and don't want to be switching gear in and out for testing. Using a power center like this is also less desirable when you're trying to simplify the chain for the cleanest power delivery in 2ch systems where it is a common recommendation to plug an amplifer directly into the wall.

Testing some equipment in a spare space, I decided it was time to to face this 12V trigger business, and fashion a proper 2.5mm cable to use with a Parasound Model 2100 preamp and HCA-1500 amplifier. Plus, it was an opportunity to break out a bunch of tools and solder some stuff.


SOURCING TRIGGER CABLES
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I remember shopping around at both Monoprice and Parts Express early on, but found MCM Electronics to have in stock the ones I wanted at a more affordable price. Parts Express didn't have much of a selection and were pretty expensive even before shipping. Monoprice didn't even have them. I later discovered Mouser Electronics for another project, and checking them out the other day, they seem to have an even greater selection for 2.5mm/3.5mm mono cables and connectors. Here are some links to saved searches on theses vendors' sites.

MCM Electronics
3.5mm Mono Cable Search | http://bit.ly/1SWviWE
2.5mm Mono Cable Search | http://bit.ly/1SWvgOy
Mouser Electronics
3.5mm Mono Cable Search | http://bit.ly/1SWuwJx
2.5mm Mono Cable Search | http://bit.ly/1SWuykl


BUILD PLAN
In the case of the Parasound Model 2100 Preamp and HCA-1500 amplifier I'm working with, I needed 2.5mm on one end, and bare wires on the other.

I could just have stripped and twisted the wires, inserted behind the bus block plates, cinched down and been done after plugging the 2.5mm end into the pre, but these wires are pretty small at only 22awg, so I wanted to try to provide a bit of protection and strain relief. I have a big variety pack of crimp on connectors from a big box tool store that just won't seem to use itself up, so I decided to use these along with some solder and heatshrink to try to make these ends a little tougher, and nice and clean.


GENERAL BUILD PROCESS
  1. Snip one of the ends off the 2.5mm mono cable (Consider sacrificing a few inches here in case you need a 2.5mm connector down the road. This way, you still have some wires to work with)
  2. Strip the jacket, revealing red and black wires (The red happens to be center/tip positive on this cable, but you should always check yours to be sure using a multimeter.)
  3. Using a heat gun, warm and strip the crimping plastic insulators from the connectors.
  4. Next, carefully strip and then tin the wires. I say carefully because they're easy to just snip right in half (I prefer the insulation score/bend/separate method I learned from @helipilotdoug when building some of his diy cables. Lightly score the insulation all around, and then bend it to separate)
  5. Measure, cut and place heat shrink on the cables for later use. (I still have to remind myself constantly to do this before I solder. Can't tell you how many times I've soldered and been proudly inspecting my work only to realize that I forgot to put the #****%* heatshrink on.)
  6. Next, crimp the connectors onto the wires.
  7. This is a sloppy fit, as expected, so I add solder to the connection for strength.
  8. Complete the heat shink process.
  9. Finish 12V trigger cable; test, enjoy and admire yourself.
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DETAIL PHOTOS
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