THE NBS UNIVERSAL POWER AMPLIFIER

A brief discussion

The Design Objectives:

1. Universal operation worldwide

The NBS Universal amplifier is fully power-factor corrected. This satisfies
regulatory requirements in the EC without seeking exemptions because it is
"too difficult". PFC means that the amplifier will draw current from the AC
mains in the most efficient manner.

The amplifier will operate over a voltage range of 85-265 Volts AC which
encompasses brownout conditions in 100V countries and high-line in 240V
countries, and everything in between.

2. Universal load tolerance

The NBS Universal amplifier will drive any load of any reasonable reactance
from 2 Ohms to open-circuit. No loudspeaker system, however demanding will
cause the amplifier any difficulty.

3. Universal input

The NBS Universal amplifier accepts both balanced and unbalanced inputs,
switch selectable. A stepped input sensitivity control allows the amplifier gain to
be ideally matched to any program source or preamplifier.

4. Universal musical experience

Aside from the ease of using the NBS Universal amplifier, the audio quality is
in the highest class. Especially noteworthy is the quality of effortlessness. Power
when you need it, clarity and transparency always. Truly the iron fist in the
velvet glove.

The accomplishing of the objectives

All the subsystems within the NBS Universal amplifier utilize very high speed switchmode techniques.

The AC mains power factor correction technology was first introduced by NBS in 2000 in an earlier power amplifier. We consider this technique to be essential to preventing harmonic contamination of the AC mains. The vast majority of amplifiers draw current from the mains in narrow bursts with very high peak value. This behavior contaminates the power quality for the amplifier itself as well as all other equipment operating on the same mains circuit.

The DC converters operate with zero current and zero voltage transitions further preventing the generation of electromagnetic interference. The output of the DC converters is tightly regulated for all conditions of AC mains voltage and power output. Very few manufacturers attempt this because it is difficult as well as expensive. However, imperfection of the DC voltage supplied to the amplifier is a first-order source of degraded performance. There is no solution but to treat the power system with the same care as the audio system. We have done that.

The power amplifiers are analog high-speed devices used in a ground-centered BTL configuration. They are supported by an energy storage system capable of supplying 300 joules. This prevents any interaction between the DC converter control and the power amplifier.

There is very little audio circuitry ahead of the power stages. The balanced input uses common-mode bootstrap technique often used in instrumentation inputs. This makes the balanced input insensitive to source imbalances which sometimes occur. The input impedance of both the balanced and unbalanced inputs is high enough to permit the use of any preamplifier.

The input sensitivity control is a stepped attenuator so it is exactly resettable.

Specifications: