NAD M2 - CONNECTING A SUBWOOFER User manual

The NAD M2 Direct Digital Amplier represents a new level of amplier performance. Combining the ultra low distortion
and noise levels of the nest linear Class A and Class AB ampliers with the efciency and streamlined signal path of
the digital amplier, the M2 is the rst implementation of a new amplier technology called Direct Digital Feedback.
Co-developed with UK based Diodes Zetex Semiconductor, and using a unique implementation of their patented DDFA
architecture, the M2 redenes what is possible with digital amplier technology.
The M2 Direct Digital Amplier represents the culmination of a decade long NAD research project, capped by three
years of intense development. The result fully justies the investment. We believe that the M2 sets new benchmarks for
both measured performance and subjective musical quality.
Masters Series M2
Direct Digital Amplier
The World’s Most Advanced Direct Digital Amplier
> Blinding Speed and Precision
Extremely wide 35-bit data path for Direct Digital
Feedback compensates without truncating any
information in the original signal. Running from a master
clock frequency of 108MHz there is enough speed to
keep a very wide amplier bandwidth and very low noise
and distortion in the audio band.
> Stunning Intimacy with the Music
Directly accepting a digital PCM input completely
eliminates the noise and distortion added by cascaded
analogue amplifying stages, as found in traditional Class
AB or even Class D ampliers. Streamlining the signal
path by eliminating several amplier stages provides a
feeling of being that much closer to the performers.
Features
> see Features continued

> Advanced Power Supplies
The M2 uses three power supplies, all of them highly
efcient switch mode types. Each channel gets its own
high current power supply in a dual mono conguration.
The Input stage and control sections get their own
dedicated supply with multiple regulated secondary
voltages for individual sections.
> Analogue Input Section
We have provided a state-of-the-art Analogue-to-Digital
converter stage for analogue sources and for those who
still choose to use a traditional analogue preamplier.
This fully balanced stage accepts both a Single Ended
input and a Balanced XLR input. Both the analogue
input buffer amp and the ADC are of the highest quality
available today.
> Digital Soft Clipping
Digital Soft Clipping prevents the harsh sound and
potential speaker damage that can result with a severely
overdriven amplier.
> Dynamic Power
Digital PowerDrive optimizes performance when driving
real loudspeakers by maintaining optimum power
delivery and lowest possible distortion. Unlike most
digital ampliers that do not have power reserves, the
M2 has excellent dynamic power capabilities.
> Digital Processor Loop
This unique feature allows the advanced user to insert
external digital lters into the signal path. The Optical
TosLink format allows fuss-free connection to Macs
where there is a wide library of crossover lters and
room correction programs. Digital outputs in both coaxial
and optical formats allow for multiple M2s for bi- or
tri-amplication of advanced loudspeaker systems.
> Effective Control
An RS-232 serial interface is exible for home
and studio use, allowing the M2 to be controlled
from the PC or via advanced control systems like
Crestron and AMX.
Features continued
Direct Digital Explained
A true digital amplier can be thought of as a Digital-to-Analogue Converter that directly drives the loudspeaker.
This describes the M2 perfectly, except to say that the M2 actually has the same level of precision as the very best low
level DACs! This technology is far more sophisticated than the Class D analogue ampliers that are often erroneously
referred to as ‘digital’ ampliers.
This level of performance is unprecedented and is made possible by application of Direct Digital Feedback.
The idea of a closed loop digital amplier is not new, but the NAD M2 is the rst practical implementation of the concept.
Feedback Reinvented
The concept of feedback is simple yet brilliant. Compare the signal at the output of the amplier with the signal at the
input; any difference is caused by the distortion of the amplier. Now, invert that difference signal and add it to the
incoming signal and the difference signal will offset and cancel out the distortion. This is how it’s done in conventional
linear ampliers.

Pulse Width Correction actively adjusts the pulse width (PCM to PWM conversion) to compensate for amplier
non-linearity.
Power Supply Feedback is a scheme where the power supply voltage is monitored and the amplier gain is adjusted,
compensating for pulse amplitude errors.
Pre-correction is a static compensation for known amplier non-linearities.
Direct Digital Feedback operates simply by determining the pulse area error, no matter what the cause, and passing this
information back to the digital domain where compensation can be made. This method calls for all distortion mechanisms
regardless of their source.
The New Frontier
As proven by our recent Masters Series ampliers (M3, M25), NAD has brought the performance of the Linear Class AB
amplier very close to theoretical perfection. The next frontier for improved performance is the digital amplier.
Now the M2 provides a benchmark for performance, both measured and subjective, in the new world of digital
amplication. Highly efcient, immensely powerful and musically revealing and involving, the M2 Direct Digital Amplier
takes its place among the world’s best ampliers regardless of price or design philosophy.
But for a digital amplier implementing this simple concept is anything but simple! As we have pointed out, the M2 takes
a digital input signal and outputs an analogue signal to drive the loudspeaker.
The conventional feedback architecture with a loop from the output to the amplier’s input is too slow and not a successful
approach with a digital amplier, so the direct digital feedback technology was developed to deliver the solution.
A feedback error signal is generated by comparing an extremely pure PWM reference and then converts to the digital
domain for digital correction. This loop correction, occurring once every 9 trillions of a second, assures the highest levels
of speed and accuracy. This very direct feedback approach is at the heart of the M2 architecture.
Some limited forms of feedback have been used successfully before in PWM-based amps. The common problems
with digital amplication and the various solutions are shown in the table below:

2 X 250W Continuous Power at 8 and 4 Ohms
>500W Dynamic Power, 22A Peak Current
<0.004% THD 20Hz – 20kHz from 500mW to 250W
>120dB Dynamic Range
40uV Residual Noise
>2000 Damping Factor at 50Hz
+0/-0.5dB Frequency Response 20Hz – 20kHz, -3dB >85kHz
Channel Separation >90dB @ 1kHz, >80dB @ 10kHz
FEATURES
Digital PowerDrive
Digital Soft Clipping (switchable)
5 Position Digital Impedance Compensation Filter
Remote Control
CONNECTIVITY
Analogue
A/D Conversion for Analogue Inputs
Multi-bit Delta/Sigma 24/192kHz
0.0004% THD
124dB S/N Ratio
High Resolution 120dB Digital Attenuator
Digital
Inputs Digital SPDIF: AES/EBU, Coaxial X 2, Optical X 2
Inputs Analogue: Balanced, Single Ended
Processor Loop: SPDIF Optical (Mac compatible)
Rear Panel
2 Sets of Speaker Binding Posts to facilitate Bi-wiring
RS-232 serial data port
IR Input
12V Trigger Input and Output
GENERAL
Standby Consumption
Amplier Efciency
Power Requirements
Unit Dimension (W x H x D) Gross*
Net weight
Shipping weight
M2
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1W
90%
100 - 240V AC 50/60 Hz
435 x 148 x 502mm
20.2kg
25.6 kg
Features and Specications
NAD Electronics International reserves the right to change specications or features without notice. NAD is a registered trademark of NAD Electronics
International. All rights reserved. No part of this publication may be reproduced, stored, or transmitted in any form whatsoever without the written
permission of NAD Electronics International. © 12/09 NAD Electronics International.
www.NADelectronics.com
*Gross dimensions include feet, extended buttons and rear panel terminals. Note: Installers should allow a minimum clearance of 55mm for wire/cable management.
435.00 mm
148.00 mm
501.68 mm