Big Bang from a Little Box

A mini amplifier powers huge speakers using technology from satellites

Building a traditional amplifier isn’t rocket science, but making a digital one that’s a fraction of the size and just as powerful is. Part of a wireless music-streaming system, the tiny Sonos Zone Player ZP120 is able to drive giant speakers like the B&W 803s [pictured] using the same kind of power supply found in satellites.

Analog amplifiers take a weak signal from a CD player or other input and ramp up the voltage until it’s powerful enough for the speakers. But most of the electricity used to build up the power leaks out as heat, requiring a bulky metal radiator to dissipate it. A typical digital amp is more efficient because it jumps straight from the input to the output voltage. But it’s mated to a power supply that always delivers the same level of power, much of which is wasted.

The ZP120 instead uses a resonant switching power supply (RSPS), which delivers precisely the amount of power that the digital amp demands. To produce 110 watts of output, the ZP120 needs just 125 watts of power. An analog amp requires about 400 watts.

Satellites use RSPS to protect sensitive components from heat. But the rapidly changing voltages generate electromagnetic interference that would create a hum from an audio amp. To prevent that, Sonos designed filters to block any stray frequencies that the power supply produces.

Expect to see RSPS appear in more home theater products in the next few years—as technology from outer space helps you conserve the limited inner space of your stereo rack.