AV Receiver Reviews

Bottom Line

Cambridge Audio’s Azur 751R is beautifully built and meticulously finished — and its price reflects it. None of my ergonomics-related grumblings above should take away from the truth that its audio/video performance was powerful, pristine, and without any weaknesses I could uncover. If your ideal of A/V system architecture is a setup that you tweak and calibrate only once and then simply use day-to-day, adjusting little beyond the volume control — and if cost is not an overwhelming consideration — you will be pleased. Delighted. Thrilled. Yes, the Azur 751R sounds that good.

Test Bench / Power Output

When I tested Cambridge’s Azur 551R receiver just about a year ago, I found superb performance throughout. The new, more powerful 751R matched that feat nearly perfectly (the one exception being D/A linearity, which I’ll return to) while adding a substantial power boost. The 751R looks extremely similar to the 551R and is not all that much larger (about 1.5 inches), yet our review sample produced almost 2 dB more power in every test — including the most challenging, all-7-channels one, where the 751R posted an impressive 125 watts with all channels at their clipping point simultaneously.

Noise, distortion, and frequency response were all exceptionally good across the board, as was true with the earlier model. However, as I alluded to above, the 751R’s digital-to-analog linearity — that is, its amplitude accuracy with very small signals reflecting the 2 or 3 “least significant” bits of digital words — was actually inferior to that of the less expensive 551R. The 751R’s linearity was essentially perfect at –70 dBFS, but it showed error of around 6 dB at –90 dBFS, which suggests a rounding error or possibly a time-domain equivalent (time and amplitude are inextricably intertwined in massively oversampling converters like the Cambridge’s). Thus, and almost certainly in consequence, the 751R’s signal-to-noise results and S&V-specific “excess noise” ranged from 0.5 dB to a few dB inferior to the earlier model’s. This is not such a big deal since we’re on the ragged edge of theoretical perfection here anyway, and it does nothing to counter my very positive response to the Cambridge receiver’s audible performance, which was outstanding.

DOLBY DIGITAL PERFORMANCE

All data were obtained from various test DVDs using 16-bit dithered test signals, which set limits on measured distortion and noise performance. Reference input level is –20 dBFS, and reference output is 1 watt into 8 ohms. Volume setting for reference level was –18. All level trims at zero, except for subwoofer-related tests; all speakers were set to “large,” subwoofer on. All are worst-case figures where applicable.

Output at clipping (1 kHz into 8/4 ohms)
     1 channel driven: 239/325W (23.8/25.1 dBW)
     5 channels driven (8 ohms): 146W (21.6 dBW)
     7 channels driven (8 ohms): 125W (21 dBW)
Distortion at 1 watt (THD+N, 1 kHz), 8/4 ohms: 0.03/0.03%
Noise level (A-wtd): –74.7 dB
Excess noise (with sine tone),16-bit (EN16): 0.6 dB
Frequency response: 20 Hz to 20 kHz<br>+0.1, -0 dB

STEREO PERFORMANCE, MULTICHANNEL INPUT

Reference input and output level is 200 mV; volume setting for reference output level was –19.

Distortion (THD+N, 1 kHz, 8 ohms): 0.03%
Noise level (A-wtd): –81.1
Frequency response: <10 Hz to 160 kHz: +0, –3 dB

STEREO PERFORMANCE, DIGITAL INPUT

Reference level is –20 dBFS; all level trims at zero. Volume setting for reference level was –17.5.

Output at clipping (1 kHz, 8/4 ohms, both channels driven): 208/273W (23.2/24.4 dBW)
Distortion at reference level: 0.02%
Linearity error (at –90 dBFS): 6 dB (see Notes)
Noise level (A-wtd): –74.9 dB
     with 96-kHz/24-bit signals: –84.5 dB
Excess noise (with/without sine tone)
     16-bit (EN16): 0.8/5.0 dB
     quasi-20-bit (EN20): 10.5/11.3 dB
Noise modulation: 0.4 dB
Frequency response: <10 Hz to 20 kHz; 0.1, –0 dB
with 96-kHz/24-bit signals:<br>+0.2, -3 dB at 44.3 kHz

BASS-MANAGEMENT PERFORMANCE

Measured results obtained with Dolby Digital test signals.

Subwoofer-output frequency response (crossover set to 80 Hz): 16 dB/octave (approx.) above –3-dB rolloff point of 80 Hz
High-pass-filter frequency response (crossover set to 80 Hz): 12 dB/octave below –3-dB rolloff point of 80 Hz
Maximum unclipped subwoofer output (trim at 0): 3.7V
Subwoofer distortion (from 6-channel, 30-Hz, 0-dBFS signal; subwoofer trim set to 0): 0.2%
Crossover consistency: bass crossover frequency and slope were consistent for all sources and formats.
Speaker size selection: all channels can be set to “small.”
Speaker-distance compensation: available for all main channels.

Notes

When I tested Cambridge’s Azur 551R receiver just about a year ago, I found superb performance throughout. The new, more powerful 751R matched that feat nearly perfectly (the one exception being D/A linearity, which I’ll return to) while adding a substantial power boost. The 751R looks extremely similar to the 551R and is not all that much larger (about 1.5 inches), yet our review sample produced almost 2 dB more power in every test — including the most challenging, all-7-channels one, where the 751R posted an impressive 125 watts with all channels at their clipping point simultaneously.

Noise, distortion, and frequency response were all exceptionally good across the board, as was true with the earlier model. However, as I alluded to above, the 751R’s digital-to-analog linearity — that is, its amplitude accuracy with very small signals reflecting the 2 or 3 “least significant” bits of digital words — was actually inferior to that of the less expensive 551R. The 751R’s linearity was essentially perfect at –70 dBFS, but it showed error of around 6 dB at –90 dBFS, which suggests a rounding error or possibly a time-domain equivalent (time and amplitude are inextricably intertwined in massively oversampling converters like the Cambridge’s). Thus, and almost certainly in consequence, the 751R’s signal-to-noise results and S&V-specific “excess noise” ranged from 0.5 dB to a few dB inferior to the earlier model’s. This is not such a big deal since we’re on the ragged edge of theoretical perfection here anyway, and it does nothing to counter my very positive response to the Cambridge receiver’s audible performance, which was outstanding. —D.K.