Center positive vs. Center negative for scratch builder?

Discussion in 'Burnt Fingers DIY Effects' started by drneilmb, Jun 30, 2020 at 11:36 PM.

  1. drneilmb

    drneilmb Tele-Meister

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    I'm just starting out building my own pedals. In fact, I'm just starting out with pedals at all. I own zero pedals. I built a boost pedal from scratch using a 9V battery and it's so fun that I decided that I want to package it up and build some more. I'm going to start with a power supply using a 12V 2A wall wart and some 7809 regulators.

    But here's my problem: everything in my workshop and ham radio shack is center-positive on the DC 5.5x2.1mm jacks/plugs. I've got loads of power supplies and cables and radios and test equipment and audio gear, much of it homemade, that uses these same plugs with what I always thought of as the "standard" center-positive polarity. Now along comes this pedal power supply and my first boost pedal and I'm wondering which polarity to choose?

    If I build my power supply as center positive, then I can use it with other stuff in the workshop, but if I ever get any commercial pedals, then I have to wire up some crossed cables and remember to never get them mixed up and use the wrong ones on the wrong pedals. If I build my power supply and pedals as center negative, then I can never use any of the other power supplies in the workshop, but I'll be fine if I get some commercial pedals down the line.

    Has anyone else faced this issue before? Is there a simple solution that I'm overlooking? Besides lots of fluorescent yellow tape and a multimeter close at hand?

    Which would you choose?

    Thanks in advance for any suggestions you might have.

    -Neil
     
  2. tubegeek

    tubegeek Tele-Afflicted

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    I think the reason is so the switched DC jacks will easily supersede the battery power in a pedal and simultaneously you can switch the power on & off by using a 1/4" TS plug in a TRS jack.

    In other words, it became a convention because the whole system did something useful. HAM builders didn't give a hoot about interoperability with battery powered gear etc.
     
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  3. Armo

    Armo Tele-Holic

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  4. DougM

    DougM Friend of Leo's

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    Radio Shack used to make a kind of universal adapter that had several different plug sizes and types, and the most common one we have on pedals could be either polarity. You'd just pop it off, turn it 180 degrees and pop it back on and the polarity would then be the opposite from before.
     
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  5. zippofan

    zippofan Tele-Afflicted

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    Still have some of those old Radio Shack adapters around here somewhere...

    That is a dilemma, I know I get really concerned about my positive ground pedals when setting up power for a mixed group. You could always stick to positive ground circuits like a Fuzz Face, Rangemaster. ;)

    I'm kidding, I wish I had an answer other than being really careful marking and using mixed adapters.
     
  6. Peegoo

    Peegoo Friend of Leo's

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    Since you're 'rolling your own' and you already have your own power standards for your shop, build center positive. There is no good reason for you to conform to industry standard.

    A short adapter cable is a cinch to cobble up--should you decide to incorporate commercial pedals into your rig.

    One thing that prevents the Magic Smoke from escaping a pedal circuit is to place a diode in series on the power jack. If you're not currently doing this, consider it because it can prevent you smoking a circuit.

    A few pedal makers do this because it's cheap insurance in the event of reverse polarity on the DC power input. However, many makers do not include this because two extra pennies of production cost cuts into their profits.
     
    Last edited: Jul 1, 2020 at 6:57 AM
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  7. jvin248

    jvin248 Poster Extraordinaire

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    Center positive from an engineering perspective is the best plan, however you'll get other pedals someday or give one of your pedals to a buddy someday and having it reversed from conventional pedals will make the process challenging. Local music shop gave me a pedal to try fixing that was a return from a customer "pedal quit working" and the first thing I saw was a center positive plug setup. I have also seen damage from using random power bricks at higher voltages .. just because the plug fits does not mean the power is correct.

    Boss Pedals would be the benchmark for most. If you match to those then that is the safest design.

    .
     
  8. drneilmb

    drneilmb Tele-Meister

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    Okay, cool, thanks for the thoughts everyone. I don't need switched power or internal batteries, so I'll go with my standard orientation and build my pedals to match.

    If I ever get commercial gear and want to use it with the same power supply, it's easy enough to build an adapter cable that switches the conductors. Heck, I do that half the time by accident. :) I bought a bunch of cable-mount plugs and zip cord to make my own cables, so I'll just save a couple and put them on backwards and mark them with a bunch of yellow tape if I ever need to.

    -Neil
     
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