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Boss AB2 power jack mod

Discussion in 'Burnt Fingers DIY Effects' started by laird, Feb 17, 2011.

  1. laird

    laird Tele-Holic

    741
    Jul 8, 2009
    Palm Harbor, FL
    (permalink: http://laird.vectorstar.com/music/pedals/bossab2)

    The Boss AB2 is a relatively inexpensive and readily available buffered A/B footswitch. It suffers from one critical problem: it cannot be powered by a pedalboard supply. Boss decided to make this pedal run only from a pair of AAA batteries stored inside the unit, which must be disassembled to change. And if the batteries die, no sound gets through because it's a buffered pedal. Because of these problems, the AB2 is a rare sight to see on pedalboards, but that can be fixed with just a few parts and a few minutes of work.

    Modifying this footswitch to run from a standard 9V DC pedalboard supply is fairly simple. The parts needed are:

    * Insulated plastic DC power jack (like this one) - metal jacks will NOT work!
    * Two 680 ohm 1/2-watt resistors
    * Three inches of 20-gauge stranded wire
    * (Optional but not recommended) 9V battery connector

    The tools needed are:

    * #1 Philips screwdriver
    * Jeweler's Philips screwdriver
    * Needle nose pliers or 1/2" hex socket (to remove nuts from 1/4" jacks)
    * Wire snips/strippers
    * 1/8" drill bit
    * 1/2" Uni-bit (like these)
    * Soldering Iron
    * (Optional) center punch
    * (Optional) High-speed rotary tool with carbide cutter to clean up drill hole
    * (Optional) voltmeter or multimeter

    Getting Started

    Remove the hex nuts on the three 1/4" jacks. Remove the two screws on the back and open the case. Remove the 2xAAA holder and unsolder the two wires from the PCB. Remove the two screws that hold the PCB to the case. The PCB should now be removable, but leave it in place for the moment.

    There is a free space in the case that is just the right size for a DC jack. There is just enough space to fit the jack, but we have to be careful to choose our center point wisely. If it's too close to the PCB, we won't be able to reinstall the board. If we're too close to the bottom of the case, the metal securing nut won't be able to fit. Eyeball for a spot evenly centered between the PCB and the bottom of the case, and if you have a center punch, use it to mark the spot. Now, remove the PCB from the case.

    Breaking Stuff

    On the underside of the PCB, near where our power jack is going to go, there's a little black electrolytic capacitor. Mine was laying down across the PCB and would have blocked the jack from going in, so I carefully stood it up, then bent it down alongside the input jack. This provided the necessary clearance for the jack and PCB to coexist.

    With the 1/8" drill bit, drill the hole marked in the last step. Then use the 1/2" Uni-bit to slowly widen the hole all the way to 1/2". My plastic jack was just the slightest bit larger than 1/2", so I used my dremel to carefully clean up around the drill hole and open it just enough for the jack to go through smoothly. Put the securing nut in place. Due to the tight clearance with the bottom of the case, you may need to spin the power jack in order to tighten the nut.

    Burning Fingers

    Now, solder your short length of 20-gauge wire to the tip lug on the jack. Solder a 680-ohm resistor to the sleeve lug. Optionally, you can install a 9V battery adapter by hooking the black to the tip lug and the red to the momentary sleeve lug. If in doubt, see the picture on the link above to the DC power jack. Bend the black wire and 680-ohm resistor so they stick out the side of the case.

    Reinstall the PCB. You can install the two PCB screws and three hex nuts now. Take your second 680-ohm resistor and bend its leads as shown in the photos below, so the leads sit naturally on the PCB's "RED" and "BLACK" soldering pads. Route the black wire down past the notch in the PCB, then back to the "BLACK" pad. Solder the black wire and resistor to the "BLACK" pad. Now, bend the 680-ohm resistor from the DC jack up so its lead lays naturally on the "RED" pad. Make sure there is enough clearance so this resistor does not touch the case when it is reinstalled. Solder the 680-ohm resistors to the "RED" pad.

    Testing

    This circuit was designed to run at about 3V. Prior to hacking up the pedal I measured the voltage with two AAAs and the input jack inserted at 2.6V. If you installed a 9V battery connector, plug in a 9V battery and measure the voltage across the "RED" and "BLACK" soldering pads. You should read about 4.5V with nothing plugged into the pedal. Now plug in a cable to the input jack, so the pedal powers on. Recheck the voltage. With a fresh battery I measured 2.7V. Now, plug in your pedalboard supply and measure the voltage. I measured 2.8V. Anything from 2.5 to 3.3V will be adequate. I've been running mine like this for over two years and it hasn't burnt out yet.

    We're all done! Close the case and reinstall the two screws on the bottom.

    About the 9V battery

    Although I included instructions for including the 9V battery connector, I don't recommend installing one. Due to the 680-ohm resistor sitting between the red and black pads, a 9V battery left in this pedal (even when off) will be discharged within a few days. Maybe someone else can suggest a way to wire the plug so the battery is unloaded when no DC jack is plugged in.

    -Laird
     

    Attached Files:

  2. ToadLC

    ToadLC Tele-Meister

    499
    Apr 14, 2008
    Sacramento
    Beavis to the rescue! Check the page in the link below to wire it up so when the plug is removed from the IN jack it disconnects the battery. You may need to replace the IN jack with a stereo jack if it doesn't have on.

    http://www.beavisaudio.com/techpages/PedalPower/
     
  3. Flatfoot

    Flatfoot Tele-Meister

    302
    Sep 17, 2009
    Southern Missouri
    I just performed this mod, sans the 9v battery clip, on my AB2 last night. Really neat - works like a charm and has already been afixed to my pedal board. :lol:
     
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  5. czech-one-2

    czech-one-2 Friend of Leo's

    Oct 3, 2008
    Prague
    Ressurecting this old thread cause I think its a great idea as my A/B 2 really eats batteries. Gonna try this one, thanks for the tip! :cool:
     
  6. Obsessed

    Obsessed Poster Extraordinaire

    Nov 21, 2012
    Montana
    Thanks for bringing this to my attention. I've been putting off getting the AB-2, just because of the battery issue. Now it is a no brainer for me.
     
  7. limbe

    limbe Tele-Afflicted

    Sep 4, 2009
    Stockholm,Sweden
    I use a very simple method for old (read vintage) pedals to enable them to work on both wall warts/batteries.(I´m nearly too embarrassed to post it) If I just want to use the pedal with a wall wart,I make a special cord that on one end has a plug that suits my power supply and on the other has a connector that suits a 9 volts batteri.I remove the back plate and connect the identical connectors together.(The connector from the power supply has the polarities reversed.) I put the pedal together with three screws so the cord won´t short out.If the power supply fails I have a fresh 9volt battery inside that´s insulated.All this because I can´t bring myself to drill a hole in a vintage pedal.Sometimes there´s not enough space for both a jack and a battery.
     
  8. andyg_prs

    andyg_prs NEW MEMBER!

    1
    Sep 1, 2012
    Stroud
    Reviving this thread as I am about to buy an AB-2 and would like to perform this mod.

    There was a link to a way to wire such that a 9v battery could be left in the pedal but so that it wouldn't discharge when the pedal isn't in use....

    Any ideas?

    Thanks,
    Andy
     
  9. ohm-ish

    ohm-ish NEW MEMBER!

    1
    Dec 10, 2015
    Copenhagen
    Forgive me for reviving this old but good thread :)
    I just bought a Boss AB-2, not knowing it required batteries.. And so I want to install this DC mod.

    Laird, is your mod still functioning? ;)
    And can you please tell me if the resistors need to be 1/2 watts?
    I heard that higher wattage could be better / cooler / more durable.

    Cheers
     
  10. Muzik4Machines

    Muzik4Machines TDPRI Member

    85
    Nov 17, 2015
    quebec
  11. czech-one-2

    czech-one-2 Friend of Leo's

    Oct 3, 2008
    Prague
    Yeah, interested in that battery drain fix. Can someone find/renew that Beavisaudio perma-link?
     
  12. matmosphere

    matmosphere Tele-Meister

    128
    May 27, 2015
    District of Columbia
    Some of the Beavis audio stuff is archived online, but unfortunately the site isn't up anymore. The link you want might be here:

    http://archive.is/www.beavisaudio.com

    That is about all I could find last time I looked.
     
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