Power Amplifiers

Mark Levinson No 53 Monoblock Power Amplifier


On the Bench

As with some of my previous reviews, I used one of my Carver speakers as the load for some of the tests.

With a 1 kHz sine wave and 10 volts into the Carver speaker, THD+N was a very, very low 0.002%. The second harmonic is the largest one, which is a good thing.


IMD was 0.02%, again, into the Carver speaker.


Using a combination of 19 kHz and 20 kHz sine waves, the B-A (20 kHz minus 19 kHz) peak at 1 kHz was 100 dB below the fundamentals.


THD+N vs. Frequency into the Carver speaker yielded a curve where the distortion peaks at 8 kHz.


Here is an impedance/phase plot for the Carver speaker. Notice that the region between 3 kHz and 8 kHz has low impedance coupled with 650 phase, which is the most difficult area of the speaker's impedance to handle. That is why the distortion in the curve shown above peaks in the same region.


The measured frequency response was 20 Hz to 50 kHz, - 0.3 dB.


Power output into an 8 ohm load showed the sharp knee at 500 watts, with clipping (1% THD+N) at 600 watts.


At 4 ohms, the hard knee was at 800 watts, with clipping at 900 watts. However, there was so much voltage drop out of the AC socket (about 108 volts instead of 120), I am sure this low voltage supply was the reason. I have no doubt this amplifier will deliver full spec output. It is getting to the point that today's amplifiers are so powerful, we may need to install voltage regulators as an integral part of our home theater systems.