Power Amplifiers
Classe CA-M600 Monoblock Power Amplifier
- Written by John E. Johnson, Jr.
- Published on 21 February 2011
On the Bench
Distortion measurements were made within an 80 kHz bandwidth. Some tests were performed with the amplifier driving one of the Carver speakers, while others used an 8 ohm power resistor.
At 1 kHz and 10 volts into the Carver speaker, THD+N was a miniscule 0.001%.
IMD, using the SMPTE standard of 60 Hz and 7 kHz sine waves at a 4:1 ratio, was 0.002%. This is superb performance.
Using 19 kHz and 20 kHz sine wave test signals, the B-A peak at 1 kHz was 122 dB below the fundamentals.
THD+N vs. Frequency into the Carver speaker was flat out to about 5 kHz and then rose steadily up to 50 kHz.
Here is an Impedance - Phase plot of the Carver speaker. The region around 5 kHz, where the impedance is low and the phase is - 650, is very difficult for amplifiers to drive, and that is part of the reason the distortion goes up in that frequency range in the graph shown above.
The measured frequency response was down 0.3 dB at 20 kHz, and down 3 dB at 100 kHz, for both 8 ohms and 4 ohms, which is right on the specification.
THD+N vs. Power Output resulted in the sharp knee at 650 watts into 8 ohms, and clipping (1% THD+N) at 700 watts. With a 4 ohm load, the sharp knee was at 900 watts, with clipping at 1,200 watts.
