The highish noise levels for analog sources mean that the percentage of distortion when plotted against output power (fig.14) is actually dominated by noise. But this little receiver more than meets its specified output power, even with both channels driven continuously. For our standard 1% THD+noise clipping point, I measured 30.1Wpc into 8 ohms (14.8dBW), 39Wpc into 4 ohms (12.9dBW), and, with one channel driven continuously, 60.5W into 2 ohms (11.8dBW). With a low-duty-cycle 1kHz toneburst (10 cycles on, 4000 cycles off)—which is more representative of how the amplifier will behave with a music signal and with just one channel driven—even more power was available at the 1% THD clipping point (fig.15): 52.3W into 8 ohms (black trace), 83W into 4 ohms (red), and 104.6W into 2 ohms (blue). Even into the punitive 1 ohm load, the RP-U100 still managed to put out 96.4W (green trace)!

Fig.14 Yamaha RP-U100, distortion (%) vs continuous output power into (from bottom to top) 8 ohms, 4 ohms, and 2 ohms.

Fig.15 Yamaha RP-U100, distortion (%) vs 1kHz-burst output power into 8 ohms (black trace), 4 ohms (red), 2 ohms (blue), and 1 ohm (green).

Less power was available in the bass on this test (54.3W at 50Hz into 4 ohms), but, given its nearfield listening use, it's hard to imagine the Yamaha being bothered by any real loudspeaker load. Certainly it worked very well with the Evett & Shaw speakers I used, which dip to just 1.2 ohms between 400Hz and 500Hz.

Considering how little it costs and how many features it offers, the RP-U100 measures surprisingly well, particular regarding its output amplifier stage. Achieving good sound at this price level is all about the product's designers engineering appropriate compromises, and this Yamaha appears to have done.—John Atkinson