Pure Class-A the Ultimate Headphone Amplifier


  • A high performance Alps volume control
  • XLR connectors for operating in “”Balanced Headphone Mode”” (see above)
  • A linear power supply comprised of a custom-made toroidal transformer and extensive capacitor reserves.



The Optoma 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 Optoma 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.

Technology & Craft

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.
Furthermore, the single output transistor is operated with a rock-solid constant-current bias, which provides for very stable control over the output signal at all times. Musical waveform accuracy is maintained such that typical “”overshoot”” and “”ringing”” artifacts are virtually eliminated. The sonic effect is one of a fast and authoritative response manifesting as exceptionally accurate and natural transient reproduction at all frequencies and dynamic levels.
Balanced Headphone Mode:
Unique to the HA-200 is its ability to quadruple output power by simply adding a second unit and operating them together in “”Balanced Headphone Mode.”” For this configuration, all that’s needed is to use the XLR inputs and outputs on each HA-200 along with a special cable adaptor for connecting the headphones.
In Balanced Mode, four completely separate amps (2 per unit) are utilized to drive the four phases of the music signal (right normal, right inverted, left normal, left inverted). Please keep in mind though that this is NOT the same technique as mentioned above in the “”push-pull”” Class-B scenario. In Balanced Mode, all transistors are biased in Class-A so as to conduct current at all times – only the phase is inverted 180 degrees in the case of the left & right inverting amplifiers.
The primary benefit of such a design is that the available output voltage is doubled, so the actual output power is quadrupled. It also doubles the effective slew rate (the maximum change in voltage per second that an amplifier can achieve), as both amplifiers are operating in opposite phase to increase the dynamic realism of the music. While “”technically”” not a pure SE design, since Balanced Mode remains in full Class-A operation at all times it can be thought of as a “”dual SE”” architecture that retains the best of SE performance with the added benefits of higher power and better dynamic control.
Sonically, the resulting sound is completely “”grain-free,”” the soundstage is wide and deep while instruments and voices are reproduced with extreme clarity and purity of tone. The incredible power and dynamic control over the music simply must be experienced to be appreciated.
Class-A’s Modest Disadvantage:
The one slight disadvantage that Class-A amplifiers have is that transistor bias current must be set such that the output transistor continually operates in the center of its “”linear region,”” which simply speaking is the midpoint between its fully-on and fully-off limits. Therefore, regardless of the actual audio power being used Class-A amplifiers continuously consume their full-rated output power and dissipate that power in the form of waste heat.
Now in some cases this might be a serious efficiency issue, but mostly in those applications involving loudspeaker amplifiers capable of delivering several hundred watts of power. With headphone amplifiers, this is less of a concern due to their need for significantly less output capability. Nevertheless, while in operation the HA-200 will continuously consume 24W of power. In fact, that value actually exceeds the idle power consumption of a NuForce Reference 18 amplifier! The upshot is that in order to benefit from the superlative performance that the HA-200 has to offer, one must be willing to accept its somewhat lower power efficiency. In our opinion, that’s a relatively small price to pay for such a great reward, and we believe that many will agree.


Connections – InputRCA, XLR
Connections – OutputXLR, 6.3mm
Connections – ControlN/A
Power output393mW @ 16 Ohm 747mW @ 32 Ohm
383mW @ 100 Ohm
129mW @ 300 Ohm
70mW @ 600 Ohm
Recommended headphone impedance32 to 600 Ohm
Balanced mode200 Ohm, 14.6Vrms
Frequency response10Hz – 20KHz
Signal to noise ratio (SNR)106dB
Total harmonic distortion + noise ( THD + N)0.0005%
Power supply115V/230V
Weight (kg)2.2
Dimensions (W x D x H) (mm)217 x 231 x 44


+ Power cord – 1
+ Manual – 1



A bit special - taking the street price of the HA200 into the consideration, it is by far the cheapest way to use a headphone in a symmetric way. "
The HA200 is a very classy, pure and punchy performer, largely due to the Class A topology.”
“There is no distortion from this little beauty.” 
“NuForce really do know how to produce an accurate but still very natural and musical product which gave me no listening fatigue and endless fun”
“I found the HA200 to be one of the best headphone amplifiers I have heard "
The amplifier provides rich, saturated sound of an open and smooth character. It operates rhythm and dynamics with great freedom and culture. Emphasis has been placed on the correct color extraction instruments, showing their natural tonal, but also musicality. The same is true with human voices - voices sound energetically and emotionally, are perfectly presented against the background of instruments that provide solid accompaniment and background "
“The HA200 delivers a pleasing combination of clarity and substance, regardless of source. Its soundstage is broad and dynamic with plenty of headroom, and it reveals itself to be especially adept with higher frequencies.”

“Whether used in a desktop rig or with traditional analogue sources, the HA200 acquits itself admirably. It’s a simple and straightforward headphone amp that has a well-balanced and beautifully revealing sound.” "
"The HA200 amp is minimal, modern, and slick. It has the warmth and vibrancy of tube electronics, combined with the precision and clean power of solid-state.” "
"HA200 is a champion of the sound quality offered at a nice price, then maybe he deserves a Qobuzissime!“ "
“The high level of clarity offers the ability to identify each instrument,  even if a song consists of many instruments.” "
“NuForce is very strong in its ability to design products specifically to fit a market demand, particularly in the digital domain.” "

HA-200 Support