Two years ago, I sponsored a clever Kickstarter project called Ripcord (see Figure 1). The developers promised, “You already power your phones and tablets with USB. Now you can power your guitar pedals, amps, synths, and whatever else you need on-the-fly.” Ripcord, from the Irish company MyVolts, is a power cord with a USB plug at one end, a barrel plug at the other, and a tiny voltage booster in between. The circuitry is so small it fits inside the USB end. Output choices range from 5VDC (the USB standard) to 18VDC, along with 9VDC, the standard for guitar effect pedals.
Ripcord still wasn’t shipping as of this writing, but the MyVolts people gave me information that inspired two DIY solutions. They said some of my 4.5V gear, like the Korg mini kaoss pad 2, would run just fine from 5V; I’d just have to snip off the downstream end of a USB cable and attach the right connector. That connector turned out to be an EIAJ-02 barrel plug (4mm outside diameter, 1.7mm inside diameter), wired center-positive. Figure 2 shows a USB battery pack running my mini kaoss pad 2. You can also buy these cables premade.
Notice the blue box in Figure 2—the wacky MIDIPlus miniEngine. This $60 General MIDI module is also a USB battery and host. It can charge your phone or power a USB MIDI controller so you can play the miniEngine’s internal sounds. An additional five-pin MIDI input lets you play a second MIDI controller simultaneously on another channel. Most of the sounds are comically bad, but shine when layered with better synths.
The reason I originally looked into the Ripcord was to battery-power my 9V Korg Kaossilator Pro and Wavedrum, which are terrific jam-session instruments. MyVolts said that would draw too much current (the Ripcord maxes out at 1,000 milliamps). I considered wiring a 12V battery to a 3-pin voltage regulator, but 12V batteries are bulky and traditional step-down voltage regulators are hot and inefficient.
Then I discovered the DROK digital boost converter, which takes an input as low as 3V and pumps it as high as 35V (see Figure 3). There are many variations of these boards online; I paid about $8 for the DROK. Set to crank out 9V, it drew so little current that my USB battery pack would fall asleep if I didn’t quickly plug the DROK’s output into another device.
I cut the cigarette lighter plug off a RadioShack universal car power cord, screwed the wires into the DROK’s output, added an EIAJ-04 plug—5.5mm OD, 3.4mm ID, center positive—and fired up my Kaossilator Pro (see Figure 4). (Korg Volcas use this plug, too.) Switching the plug to 5.5mm OD, 2.1mm ID, center negative, I powered a Digitech delay and lovely Neunaber reverb pedal as well. The battery gauge barely budged after an hour. Best of all, I didn’t hear extra noise, a problem that sunk the Ripcord prototype.