Mark Levinson No.53
The $25,000, 500W Mark Levinson No.53 digital-switching reference monoblock amplifier made its regular non-playing appearance at CES 2012 but this time with an illuminated cutaway display, allowing its lead design engineer, Mark Seiber, to walk me through its circuitry. The transparent panel, which the display used in place of heatsinks allowed me to easily see the No.53's four major subsections (analog input stage, modulation, amplifier output stage with its eight air-core inductors, and power supply section, which is at the bottom of the chassis.
The No.53 uses eight half bridges working synchronously to achieve a much higher Pulse Wave Modulation (PWM) switching frequency of 4MHz. The eight large air-coil inductors (four can be seen in the photos) allow the circuit to avoid the inevitable dead band time in the interval when the MOSFET switching devices hand over to one another. ML's engineers call this approach "Interleaved Power Technology."
I was shown the simple notch filter board which removes high frequency spurious distortion. The presence of the inductors greatly helps the filtering, avoiding the need for a brickwall low-pass filter. I understand that this amplifier is scheduled for review in our magazine. Stay tuned!