- Written by John E. Johnson, Jr.
- Published on 18 June 2012
On the Bench
Distortion measurements were performed within an 80 kHz bandwidth, except where specified. The XLR input was used, except where noted. A Carver Mark IV quasi-ribbon speaker was used for the load, except for the THD+N vs Power Output, where an 8 ohm power resistor was used. The test signal was 10 volts RMS.
At 1 kHz, distortion was very low, at 0.002%. The third order harmonic is the predominant distortion peak.
With 19 kHz and 20 kHz sine waves, the B-A peak at 1 kHz was 107 dB below the fundamentals. There are only 4-6 peaks on either side of the 19 and 20 kHz peaks, which is very good.
IMD was a very low 0.003%. Secondary peaks in the 14 kHz region were very small, and there were no further peaks at 21 kHz and above. This is excellent performance.
THD+N vs Frequency showed one of the flattest response graphs I have yet seen in any power amplifier. Usually, there is a rise at the high end of the frequency spectrum, but there is none here.
Shown below is an Impedance and Phase plot for the Carver speaker that I used in the measurements.
At 8 ohms, the sharp knee was at 190 watts, and clipping (1% THD+N) at 230 watts.
At 4 ohms, the sharp knee was at 220 watts, and clipping at 240 watts. The output at 8 ohms vs 4 ohms was nearly identical, which is part of the NAD design. This keeps the amplifier stable into any load.
The measured frequency response (RCA input) was flat out to 20 kHz, down 0.5 dB at 50 kHz, and down 2 dB at 100 kHz.