Mark Levinson No. 53 No53, Reference Power Amplifier, Born Of Listening, The Technical Challenges

No53

REFERENCE POWER AMPLIFIER

BORN OF LISTENING

New Mark Levinson products are not introduced with the seasons, or according to arbitrary marketing schedules. They’re introduced as new technologies, which have shown promise on paper, are perfected and proven through rigorous in-house development and evaluation procedures. In the case of the No53, a highly experienced evaluation team was assembled to conduct blind and sighted listening tests of a novel switching amplifier prototype, measuring it against past and present Mark Levinson linear power amplifiers as

well as a range of competitive products.

As the development process wore on, power amplifiers deemed sonically inferior were removed from further testing. Several judges were surprised to learn that the new switching amplifier was never among them. In fact, the early No53 prototype emerged as a winner, with several panelists awarding it top honors for speed, dynamics and clarity. It was, to say the least, an unexpected result. For a mere prototype switching amplifier to hold its own against linear amplifiers that were deemed to be the very best the marketplace had to offer – time-honored Mark Levinson models included – meant we knew we were dealing with a paradigm-shifting design.

Convinced that the minor quibbles that had come up during the initial listening tests could be overcome, the No53 project was commissioned, and development of the first new Mark Levinson Reference power amplifier in more than a decade began in earnest.

THE TECHNICAL CHALLENGES

All power amplifier designs have inherent pros and cons based on their design topology, and switching designs are no exception. On the plus side, switching amplifiers are more powerful, smaller and run cooler than their

linear counterparts – by several orders of magnitude. As points of comparison, the Mark Levinson No33 is rated at 300 watts into 8 ohms, measures 31 x 14 x 31 inches and weighs in at 435 pounds, while the No53 – at 500 watts, 21 x 9 x 21 inches and 135 pounds – is nearly twice as powerful, substantially more compact and 300 pounds lighter.

The No53 is capable of generating truly phenomenal power levels to support both the instantaneous and continuous demands of virtually any speaker load. More impressive, the No53 accomplishes this feat while main- taining a constant, thermally balanced operating temper- ature. Although always warm to the touch, the operat- ing temperature of the No53 will not vary – or exhibit even the slightest change in performance capability – regardless of how long or hard the amplifier is driven.

The downside of switching power amplifiers? Because they switch output devices on and off in very rapid succession to mimic the input signal – one set of output devices drives the positive half of the waveform, and a separate set drives the negative half – switching noise and dead bands become significant design challenges.

SWITCHING OFF SWITCHING NOISE

In most switching power amplifier designs, a brick-wall filter is placed above the audio band to remove switch- ing noise. But because of the filter’s physical proximity to the audio band, this has a significant adverse effect on phase relationships, the smoothness of frequency response and imaging. In short, it degrades overall sound quality. To overcome this challenge,

Mark Levinson engineers devised Interleaved Power Technology (IPT), a patented method of raising the amplifier’s switching frequency. In the case of the No53, the switching frequency is raised to an extremely high