BHK Labs Measurements: NAD C 275BEE Stereo/Mono Amplifier

All amplifier measurements are performed independently by BHK Labs. All measurement data and graphical information displayed below are the property of the SoundStage! Network and Schneider Publishing Inc. Reproduction in any format is not permitted.

Notes: Measurements of the NAD C 275BEE power amplifier were taken at 120V AC line voltage, both channels driven. Both channels were measured, using the fixed-level inputs. Unless otherwise indicated, the data reported below are for the right channel.

Power output (stereo mode)

Power output at 1% THD+N: 192.0W @ 8 ohms, 201.0W @ 4 ohms

Power output at 10% THD+N: 203.8W @ 8 ohms, 243.8W @ 4 ohms

Power output (mono mode)

Power output at 1% THD+N: 354.1W @ 8 ohms

Power output at 10% THD+N: 468.7W @ 8 ohms

Additional data

Input/output polarity: noninverting

AC-line current draw at idle: 65.0W, 0.78A, 0.71PF

Gain (stereo, Lch/Rch): output voltage divided by input voltage, 8-ohm load Fixed input: 28.6X/28.5X, 29.1dB/29.1dB Variable input, full clockwise: 50.7X/50.0X, 34.1dB/34.0dB

Gain (mono), output voltage divided by input voltage, 8-ohm load Fixed input: 57.2X, 35.2dB Variable input, full clockwise: 101.1X, 40.1dB

Input sensitivity for 1W output into 8 ohms (stereo, Lch/Rch) Fixed input: 98.9mV/99.2mV Variable input, full clockwise: 55.8mV/56.6mV

Input sensitivity for 1W output into 8 ohms (mono) Fixed input: 59.4mV Variable input, full clockwise: 28.0mV

Output impedance @ 50Hz Stereo mode: 0.042 ohm Mono mode: 0.084 ohm

Input impedance @ 1kHz (stereo) Fixed input: 10.3k ohms Variable input, full clockwise: 205k ohms

Input impedance @ 1kHz (mono) Fixed input: 10.3k ohms Variable input, full clockwise: 163k ohms

Output noise with fixed input (stereo mode), 8-ohm load, termination 1k ohm, Lch/Rch Wideband: 0.45mV/0.33mV, -76.0dBW/-78.9dBW A weighted: 0.0257mV/0.0264mV, -100.8dBW/-100.6dBW

Output noise with variable input set full clockwise (stereo mode), 8-ohm load, termination 1k ohm, Lch/Rch Wideband: 0.38mV/0.37mV, -77.4dBW/-77.7dBW A weighted: 0.0391mV/0.0433mV, -97.2dBW/-96.3dBW

Output noise with fixed input (mono mode), 8-ohm load, termination 1k ohm Wideband: 0.70mV, -72.1dBW A weighted: 0.0540mV, -94.4dBW

Output noise with variable input set full clockwise (mono mode), 8-ohm load, termination 1k ohm Wideband: 0.64mV, -72.9dBW A weighted: 0.0821mV, -90.7dBW



Measurements summary

The C 275BEE appears to be a linear design with load-sensing circuitry that causes it to output about the same amount of power into 4 or 8 ohms; usually, a solid-state power amp produces quite a bit more power into 4 ohms.

Chart 1 shows the frequency response of the C 275BEE with varying loads. In mono mode (not shown), the high-frequency rolloff was about twice that shown in Chart 1. In both cases, the output impedance was low enough that there was negligible variation with the NHT dummy speaker load.

The distortion measured in the C 275BEE’s left channel was quite a bit better than in the right. Chart 2 illustrates how the NAD’s total harmonic distortion plus noise (THD+N) vs. power varied for 1kHz and SMPTE intermodulation test signals, and with amplifier output for 8- and 4-ohm loads. Chart 2A shows the results for 8-ohm loading in mono mode. NAD does not recommend 4-ohm loading for the C 275BEE in mono mode.

Chart 3 plots the C 275BEE’s THD+N as a function of frequency at different power levels. The rise in distortion with frequency in the right channel is quite pronounced. Chart 3A shows the same measurement taken for the left channel.

The NAD’s plot of damping factor vs. frequency, shown in Chart 4, is typical of most solid-state power amplifiers: high at low frequencies, then declining throughout the audioband. In mono mode, the damping factor (not shown) was about half that indicated in Chart 4 -- a normal situation, as the two output channels are in series with the load.

Chart 5 shows a spectrum of the C 275BEE’s harmonic distortion and noise residue in a 10W, 1kHz test signal. AC-line harmonics are low but relatively complex. Signal harmonics are dominated by the third harmonic, with the second and higher harmonics of decreasing magnitude.

Chart 1 - Frequency response of output voltage as a function of output loading

Stereo mode

Red line = open circuit

Magenta line = 8-ohm load

Blue line = 4-ohm load

Chart 2 - Distortion as a function of power output and output loading

Chart 2A

Stereo mode

(Line up at 50W to determine lines)

Top line = 4-ohm SMPTE IM distortion

Second line = 8-ohm SMPTE IM distortion

Third line = 4-ohm THD+N

Bottom line = 8-ohm THD+N

Chart 2B

Mono mode

(Line up at 100W to determine lines)

Top line = 8-ohm SMPTE IM distortion

Second line = 8-ohm THD+N

Chart 3 - Distortion as a function of power output and frequency

Chart 3A

Stereo mode

(8-ohm loading, Rch)

Red line = 1W

Magenta line = 10W

Blue line = 30W

Cyan line = 70W

Green line = 150W

Chart 3B

Stereo mode

(8-ohm loading, Lch)

Red line = 1W

Magenta line = 10W

Blue line = 70W

Cyan line = 150W

Chart 4 - Damping factor as a function of frequency

Stereo mode

Damping factor = output impedance divided into 8

Chart 5 - Distortion and noise spectrum

Stereo mode

1kHz signal at 10W into an 8-ohm load