The HA200 is a high performance headphone amplifier engineered to satisfy the requirements of the most devout headphone enthusiast. Capable of driving any set of headphones with more detail and greater scale, you will find the remarkable transparency reveals previously unheard nuances in familiar material. For the technically discerning, the HA200 utilises a purist Class-A design in a constant current configuration and offers true single ended output performance. For even greater fidelity two units can easily be configured for simultaneous use providing true balanced mode with increased transient speed and dynamic control
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" behaviour 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.
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 HA200 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" artefacts 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.
Unique to the HA200 is its ability to quadruple output power by simply adding a second unit and operating them together in "Balanced 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.
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 centre 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.
“Whether you are listening to an operatic soprano, a jazz voice, soul, blues or rock - each of the really great voices gets directly under the skin. The excellent Audeze LCD 4 acts like the tip of the injection needle at a subcutaneous injection.”
“In comparison to various other headphone amplifiers, with which I tried the LSD 4, the sound of the NuForce seems somewhat more compact, not in the sense of closeness, but rather more concentrated. Overall you really feel reminded of the sound of a very good single-ended tube amp. This combination is certainly not for everyone, but for those who like this type of music playback, they are guaranteed to be highly thrilled.”
“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.”
“In comparison to various other headphone amplifiers, with which I tried the LSD 4, the sound of the NuForce seems somewhat more compact, not in the sense of close, but rather more concentrated. Overall, you really feel reminded of the sound of a very good single-ended tube amp. This combination is certainly not for everyone, but for those who like this type of music playback, they will be highly thrilled - guaranteed."
“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.”
“I loved this little beast.”
“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”
“if you want a player that quite simply does your music justice, then this is a really good choice, and even better if you buy two”
“It is accurate, detailed but very musical and natural”
“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.”
“Just a true high-fidelity.”
“Design-wise, the HA200 is like most of NuForce’s products, alluringly compact.”
“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 dektop 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 was awarded an overall grade of “Sehr Gut” = very good (HA200 = 89,5%):
“The device offers simple construction, but immensely high-quality sound”
“It has an integrated Class-A amplifier circuit”
“The HA200 has convinced us, beginning with signal-to-noise ratio: you can turn the rotary as far as it goes without a signal input, but you will not hear any noises”
“On the positive, it also produces spacious sound...Listening to a song from Alexis Cole “Ain’t we got fun” the sweet, soft sound of the saxophone appears from front, right and from above (how the sound engineer did it, is a mystery).”
“The high level of clarity offers the ability to identify each instrument, even if a song consists of many instruments.”
“It delivers the bass in a pleasant, cautious way; hearing the plucking of the double bass is magnificent.”
The HA200 was awarded 5/5 for musicality and interest, and 4/5 for manufacturing and options.
“NuForce is very strong in its ability to design products specifically to fit a market demand, particularly in the digital domain.”
"…its ability to offer very well made equipment with innovative technologies and always for a price that could be considered reasonable.”
"From the very first seconds of listening, here we are. The HA-200 shows a vitality and joy of life rather surprising.”
“…but which contrasts with most other amplifiers , it is its definition of an extraordinary power.”
"The HA-200 amps are minimal, modern, and slick"
“They have the warmth and vibrancy of tube electronics, combined with the precision and clean power of solid-state.”
“…the 200s as monoblocks is a special experience and I've relished in it. Nothing less.”
“…NuForce’s HA-200 in monoblock form pulled off some of the best performances“
“…it offers a level of sonic integrity that make NuForce’s asking price sounds downright reasonable!”
“…because the music is so infectious with them in the system that the music keeps me going through the night”
Article By Michael Mercer
NuForce HA-200 Monoblock Headphone Amplifier Review As I sit here bobbin' my head and pumpin' my fist to Pete Rocks' remix of Yo La Tengos' "Here to Fall" I can't believe how much fun I'm having listening to music while my wifey sleeps soundly in the front room. It's crazy because the tune is not just loud; it's bumpin' at four A.M. in the morning and nobody has called the cops on me. Why? I'm rockin' a serious headphone rig! It may be bumpin' – but not for anybody else but me.