Pat Metheny, Barbican Hall, London

Time to pull the plug on this tousle-haired mechanic

Everybody loves a one-man band, and guitarist Pat Metheny's new wheeze puts him in the vanguard of that noble tradition.

As a child he was obsessed with his grandfather's player-piano; he later studied the "orchestrions" – large assemblages of instruments played mechanically – with which early 20th-century musical showmen dazzled audiences. Why not employ a combination of pneumatics and solenoid technology, he thought, to create a 21st-century mechanical orchestra? And so it was that "orchestrionics" was born: as he explains in the note to his new CD, he can "create a detailed compositional environment", and over this "open-ended platform for musical composition" he can improvise on his solo guitar.

This invites scepticism. How does this mark any advance on synthesisers and sampling? And what is a simple diatonic scale, if not an "open-ended platform"? Metheny himself willingly concedes that interesting effects don't equal good music, but since he's brought his orchestrion to the Barbican, and since he's so wide-eyed about it, we must give it a whirl.

The first three numbers make us feel we're eavesdropping on a private rumination, as he strums big-boned chords in an exploratory way; then, with a Barnum flourish, he rips down a curtain to reveal an extraordinary array of drums, bells, marimbas, hi-hats, tambourines and guitars impaled like moths in display cabinets. Then, one by one, they all swing into action, jiggling, jumping, pulsating, with winking lights adding to the fun: this could win the Turner prize as an art installation. But with Metheny's guitar booming out over the top, it's ear-damagingly loud.

And that's about it. Sometimes we get an Indian raga effect, sometimes a Malian or Cuban one. At one point, he makes his guitar sound like a tenor sax, at another like a marimba, but isn't that what bandsmen do, rather better? After his "suite" he tries to explain how it all works, but unsuccessfully. In his last piece, the amplification fails, so he summons another guitar. This fails too, and he looks at us in tousle-headed bemusement. "Switch it off and switch it on again!" shouts a voice from the crowd. Isn't this the moment to go acoustic? Alas, no. He summons yet another instrument, loses his connection once more, and gives up. "C'est magnifique," as the French marshal said of the charge of the Light Brigade, "mais ce n'est pas la guerre". Real men do it unplugged.