[M.D. Holloway]

In a clever design twist that saves cost, weight and guitar modifications associated with wiring, the Powertune system uses the guitar strings themselves to send data and power up the neck to the tuners and CPU.

All that sounds straightforward, but the system in reality is a bit more complicated. Powertune’s tuning routines have to deal with the fact that tension changes to any string can affect the tension of the other strings. The system likewise has to deal with all the ways the physics of a vibrating string can affect frequency measurements. Adams cites one example in which different attacks on the strings can produce different sets of overtone frequencies. “You really have to know what you’re doing to make this work,” Adams says.

Adams declined to give any details about the workings of the tuning algorithms other than to say they do filter out any non-useful frequencies and also account for the decay of string vibration over time. “The speed and efficiency of the algorithms are what’s really critical for us,” he says.

Speed matters because Powertune’s iterative tuning process may require several measurement and adjustment cycles – all within the time afforded by a single strum – to reach the final tuning. “So the system has to be fast,” Adams says, noting that Powertune takes just 1/10-sec to gather and process the frequency information.

Adams adds that the efficiency of the algorithms allowed him to use a low-cost, low-power 8-bit microprocessor rather than a more expensive, more power-hungry component.

Aside from tuning, the Powertune system also has a mode that helps players intonate the guitar – essentially a string-length optimization that helps the guitar play in tune up and down the neck. Some guitarists intonate the guitar themselves, making adjustments to the bridge saddle locations until the fretted and harmonic notes at the 12th fret, the midpoint of the vibrating string, match for each string. Usually, though, a guitar tech does this kind of work. And Juszkiewicz points out many guitarists don’t bother to do it at all. With Powertune’s intonation mode, the system uses lights on its LED to guide the user through the process of making the necessary adjustments by turning screws on the bridge.

Making It Fit

As much attention as Powertune’s control architecture gets, the system’s mechanical design matters every bit as much. Juszkiewicz describes the Powertune installation as “non-invasive” in that it requires no permanent modifications to the guitar. And that’s one of the key things that attracted Gibson’s interest in the first place. “Our customers don’t want to dig holes in their axe,” Juszkiewicz says. “Even with the extra electronics on board, the Robot Guitar is one-hundred-percent Les Paul.”

To keep the Les Paul looking like a Les Paul, Powertune’s CPU and power supply all squeeze into existing pockets in the guitar body, those cut for the pickup and control electronics. Adams says this packaging coup was possible in part because he built the Powertune system around small, low-power components. The power supply, for example, consists of two AA NMH batteries.With a capacity of 2100 mAh, the batteries are good for about 300 tunings, Adams says.

The only visible parts of the system are subtle and removable if need be. Adams’ biggest mechanical design coup involves the tuners themselves. Although the self-tuning system's Powerhead tuners contain a 0.5-Nm brushless DC motor, a release mechanism for manual tuning and an 18:1 worm-drive to make the string tension adjustments, they still fit into the same space as a traditional high-end manual tuning head. And Adams notes that at just 46.5 grams, the Powerhead tuners are even about 2.5 grams lighter than their manual counterparts.

On the other end of the guitar, the Powertune system requires a push-pull master control knob. Yet even its presence has been minimized by having it do double duty as one of the guitar potentiometer control knobs. In the up position, this knob controls the Powertune; in the down position it handles the guitar pot. “There’s no extra knob to add to the guitar,” says Adams.

Gibson’s Robot Guitar debuted in a limited edition in December. And one of its first players is Juszkiewicz, who raves not just about the ease of tuning but the sound of a guitar that is essentially always in tune. “The chords just sound a little bit sweeter,” he says. “Once you try it, you’ll never go back.”