Yamaha @PET RP-U100 personal receiver Measurements part 4

Like the digital inputs, the analog inputs are noninverting. The analog input impedance was 33.6k ohms at 1kHz, the maximum voltage gain into 8 ohms was a high 40.6dB. Fig.10 shows the crosstalk via the analog inputs, which should be compared with that through the digital inputs (fig.2). The sharp drop-off above 20kHz is due to the aggressive anti-alias filtering, and the decrease in channel separation below 1kHz is, again, due to power-supply coupling. But note the peculiar scalloped shape of the crosstalk traces. I have no idea what this is due to. The presence of highish levels of ultrasonic noise in the receiver's output led to a poor unweighted S/N ratio of 39.6dB ref. 1W into 8 ohms, with a wide measurement bandwidth of 10Hz-500kHz. Switching in an A-weighting filter gave a much more respectable 71.6dB ratio.

Fig.10 Yamaha RP-U100, channel separation vs frequency, analog input (10dB/vertical div., R-L dashed).

Plotting the RP-U100's small-signal distortion percentage against frequency gave a result dominated by the highish levels of noise present in the output, and so is not shown. Fig.11 reveals that what distortion is present is mainly second-harmonic in nature, and is dominated by noise. (Thirty-two readings were averaged to drop the noise below the level of the actual distortion residual in this graph.) This distortion profile is confirmed by fig.12, which shows the spectra of the Yamaha's output while it reproduced a 50Hz tone at 24W into 8 ohms, while being driven from its analog inputs. This is quite respectable behavior, as is its performance on the punishing high-level, high-frequency intermodulation test (fig.13).

Fig.11 Yamaha RP-U100, 1kHz waveform at 2W into 4 ohms (top), distortion and noise waveform with fundamental notched out (bottom, not to scale).

Fig.12 Yamaha RP-U100, spectrum of 50Hz sinewave, DC-1kHz, at 24W into 8 ohms (linear frequency scale).

Fig.13 Yamaha RP-U100, HF intermodulation spectrum, DC-24kHz, 19+20kHz at 128W into 4 ohms (linear frequency scale).

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