Would you like fries for that shake? How about phantom power for your active pickups or onboard preamp/effects?

We usually think of phantom power as related to condenser mics but I’m not talking about the 48V you get from a mixing desk here, although it is pretty much the same principle: carry your power on the same cable as your signal so you don’t have to lug around a battery. On guitars with active electronics this system is particularly useful since:

• Obviously, there’s no onboard battery: no replacing, no recharging, no making room for an aftermarket installation.
• You’re not restricted to batteries, yet you retain the option of using them: you can just as well power your pickups from any standard 9V adapter. Or go 12V or 18V if that’s your cup of tea.
• One cable fits all: the system is compatible with any guitar that has been set up to use it or any other (mono) guitar for that matter:
  • phantom-powered active guitars: all that needs to be done to the guitar is to use a stereo jack and tie tip to signal, ring to where battery (+) would be and sleeve to ground. Anyone with basic knowledge of electronics should be able to figure this out;
  • “standard” active guitars: (i.e. those with onboard batteries) if for some reason you need to use one, just short the ring to sleeve, before disconnecting power, of course. Otherwise you’d be shorting out your battery or adapter. This is necessary because most manufacturers use (or should use anyway) the “insert jack to connect battery” scheme, i.e. the battery is floating unless you short R and S together, which is what inserting a mono jack plug does. This could be accomplished with a switch.
  • passive guitars: if for some reason the original TRS recommendation is abided (which people rarely do) power would again be shorted to ground, which is hazardous if not fatal to the supply. To be safe, you could simply unplug the battery or barrel plug from the adapter or again use a switch, possibly the same one as before: a single pole on-off-on switch can choose what the ring is connected to—supply (phantom power), nothing or ground.

The diagram below shows what I’d call a typical setup: on one end you have the TRS plug (A) which goes into your guitar. On the other there is a standard TS plug (B) which plugs into the amp or effect, as usual, and an assortment of power connectors: female coaxial power connector (AKA barrel plug) (C), male coaxial power connector (D) and 9V battery (PP3) connector (E). This should assure sufficient flexibility but feel free to add female or male mini jacks, screw terminals or whatever else you like to use as power connectors. Just make sure you don’t run the risk of short circuits, like when a center-negative barrel plug touches a grounded metal enclosure or a metal jack. One alternative option is to forgo the power connectors altogether and connect it directly to the supply. This is the system I use since once you integrate it into a pedalboard it’s as easy as plug&play. Remember that switch I mentioned, though: when you plug in the ring may short to ground for a moment so it’s best to plug in and then power on (it’s always best to do that but when’s the last time you saw a guitarist remember and implement a safety procedure?).

This is by no means a free lunch, though. The system has one major drawback: if you don’t have one of these special cables around you’re pretty much screwed, your guitar will be dead unless it has the option of running in passive mode. Fortunately it’s easy as pie to make a whole bunch of these cables and keep them around. Speaking of which, remember that your signal is still riding on this cable so it must be properly shielded. Two conductor plus shield (regular 2C microphone cable) will do just fine but if you want the semi-symmetric setup you’ll need three conductors plus shield. Since we’re talking active guitars here it’s probably safe to assume that your signal is going to come from a low impedance source, so cable capacitance and resistance is less important. The question of what makes and how good is a good guitar cable is beyond the scope of this article so use whatever floats your boat. If you are using an adapter for your phantom power source though, make sure it’s properly filtered and regulated!

Note: I’ve used the term “active guitar”, which one should read as “guitar with active electronics”, be they active pickups or an onboard buffer, booster, EQ, distortion, chorus or whatever.