Mark Levinson №53 Reference Monaural Power Amplifier Technology Background

Mark Levinson №53 Reference Monaural Power Amplifier

Technology Background

Overview

Mark Levinson was founded in 1972 to produce the first solid-state electronics that
sonically outperformed the finest tube electronics of the era. In 1993, the Mark Levinson
№33 Reference Monaural Power Amplifier was hailed by audiophiles and music lovers
around the world as the ultimate power amplifier. Now, the Mark Levinson №53 debuts
– the first switching technology amplifier to sonically outperform the finest Class A or AB
amplifiers.

Cosmetically similar to its predecessor, the №53 is the first Mark Levinson Reference
Monaural Amplifier to incorporate multi-stage very high speed switching amplifier
technology, dispensing with the conventional Class AB power output stage in favor of
Interleaved Power Technology (IPT), which features a patented1 circuit design that
provides significant advantages over prior switching amplifier topologies.

PWM Limitations

Switching amplifiers aren’t new (the earliest design originated back in 1932 and was
vacuum tube-based), and offer significant advantages over conventional designs in
terms of thermal and power efficiency, and operational stability. However, while they are
popular in industrial electronics and professional sound reinforcement applications,
switching amplifier technology had yet to be refined enough to be on par with the best
conventionally configured audiophile power amplifiers.

Challenges that needed to be addressed include high frequency noise components that
are a result of the PWM process. Analogous to digital audio quantization noise, these
high frequency residual components need to be filtered with a sharp slope brickwall filter,
which can have unwanted consequences such as phase alteration and high frequency
ripple in the audio passband.

In-band distortion can also be higher than desirable, especially compared to reference
class audiophile amplifier designs.

Another area of concern is a limited frequency response range, an important
consideration in the era of modern wideband high resolution audio formats, including
SACD, Dolby TrueHD and DTS-HD Master Audio. These formats support up to 192 kHz
sampling, allowing an audio passband that extends to over four times that of standard
resolution formats such as CD.

1

Covered under one or more U.S. patents, including #5,657,219, #6,297,975 B1, #6,504,348 B2,

#6,556,053 B2, #6,909,321 B2

New Class I Interleaved Output Stage

Our engineers set out to develop a new PWM output stage design that would overcome
these limitations, based on improvements made to earlier designs employed in pro
sound reinforcement and automotive audio applications.

With conventional switching amplifier designs (Class D and other variants), the output
stage is theoretically limited to a single interleaving topology, which limits the audio
passband frequency range, and results in high order distortion products that must be
filtered out with brickwall filter types, which can introduce phase errors and other in­band artifacts. Care must be taken to ensure timing accuracy, as dead time (brief
moments where neither the positive or negative stages are conducting current between
pulses) and overlap (brief moments where both positive and negative output stages are
simultaneously conducting current, which is a catastrophic condition that can cause
amplifier failure) must be thoroughly addressed.

With our Interleaved Power Technology, there are eight half bridges (N=8) working
synchronously to achieve a much higher PWM switching frequency (4 MHz). The
modulation circuitry also features propriety refinements to ensure that there is
absolutely zero dead time between pulses, as well as completely preventing the
possibility of overlap.

The charts below detail the tremendous improvements in bandwidth and low distortion
provided by our Interleaved Power Technology (N=8), compared to conventional Class
D (N=1) techniques.

Sample Standard Class D output (N=1) 100 kHz, sidebands and odd harmonics are all present

Sample IPT (N=8) with extremely marginal residuals around 800 kHz

With Interleaved Power Technology (N=8), the comparably much smaller byproducts of
the PWM switching process are easily filtered out using a simple high frequency notch
filter, which has no deleterious effect on sound quality, compared to brickwall filter types.

And, the broad frequency response provided by our Interleaved Power Technology
system is ideal for the latest wideband high resolution audio formats, with extended
response all the way out to 95 kHz (-3dB, 8 ohms).

№53 Configuration & Construction

Within the №53, there are essentially four major sub-sections, including analog,
modulation, amplifier and power supply sections.

The analog input stage features both single-ended (unbalanced) and balanced (XLR)
inputs. Single-ended inputs are converted to true balanced configuration, and remain
balanced through the entire amplifier and on to the bi-wiring compatible speaker
terminals.

The modulation section incorporates the heart of the Interleaved Power Technology,
and features a six layer PCB with approximately 1,500 parts, and contains four isolated
modulator sections. As well, the modulator board includes communication support for
our Link2 and MLNet system control functions, along with most of the amplifier’s
protection circuitry.