Optoma HA200 - Manual (Page 3)

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NuForce HA-200 Headphone Amplifier
INTRODUCTION
The NuForce HA-200 is a high performance, Single Ended, Class-A Headphone Amplifier engineered to satisfy the
requirements of the most devout headphone enthusiast.
As personal music listening and headphone use has become an ever-greater part of the audio market, the desire
for uncompromised headphone amplification among devout enthusiasts has increased accordingly. The HA-200
was developed to specifically meet this need by uniting the most musically accurate technology available along
with renowned NuForce value.
As an ultimate high-performance headphone amplifier, the HA-200 starts out with Class-A design and then
combines that with a constant current output topology. Furthermore, when it is operated in classic Stereo Mode
it also offers true Single-Ended (SE) output performance. As a valuable plus, two units can easily be combined to
provide true Balanced Headphone Mode operation, which quadruples the available output power (2X voltage =
4X power) while increasing transient speed and dynamic control over the music.
Features
Class-A Topology
The Class-A topology is widely recognized as being the purest form of amplification, and this is because other
topologies such as Class B and Class-AB require that two output devices be operated in “push–pull” fashion in
order for each to handle one half of the musical waveform. At the point where a given device “hands off” to its
opposing counterpart, it must “turn off” or stop conducting current until the waveform polarity ultimately returns
to that which the device was assigned to handle. Then and only then will that device begin to conduct current
again, while in turn, the opposing device must now stop conducting. This “sharing of polarity” behavior leads to
what is commonly termed “crossover” or “notch” distortion.
Due to the battery-like type of charge storage within them and their inherent speed limitations, the transition
between opposing output devices can never be perfectly aligned in time to produce a seamless flow of electrical
current. Typically, a small discontinuity or “notch” at the zero-crossing (crossover) point can always be observed
by an oscilloscope connected to the output terminals of the amplifier. This notch represents distortion and is of a
static nature, meaning its amplitude remains the same at all signal levels. Therefore, this distortion represents an
ever-increasing percentage of the total output as power levels are reduced, and contributes to a “grainy” sound
that is particularly audible and quite irritating at low listening levels.
Conversely, in Class-A operation the output device is never completely shut off, so there is no “turn on” or “turn
off”” time requirement, per se. Hence, there are no issues with charge storage or any ensuing crossover distortion.
Class-A designs generally offer better high frequency performance and over-all feedback loop stability. This
second point is especially important because all amplifiers produce some distortion, but compared to other
topologies Class-A’s superior feedback loop stability means that fewer high-order distortion harmonics are
generated. The result is a more natural and harmonically accurate reproduction that is significantly less fatiguing.
Single-Ended (SE) Design
One unique advantage of Class-A design is the ability to employ only a single output device, with the technique
commonly referred to as Single-Ended design. Quite simply, such a configuration guarantees that there is no
opportunity for the generation of crossover distortion, and therefore is considered by many to be the purist form
of amplification possible. The HA-200 operates in full SE Mode when used in its stock stereo configuration.