ACCUSTIC ARTS® AMP II – MK 3: The 3rd generation

NEW for version MK 3: ACCUSTIC ARTS® damping factor linearization

The long-term hit and classic in the ACCUSTIC ARTS® range is without doubt our solid AMP II power amplifier. In 1997, the year when ACCUSTIC ARTS was founded, the AMP II was one of our first products. Now, in the 3rd generation, we have hardly changed the look of the product at all. This is because in our opinion you shouldn’t change a classic, but rather continue to further develop it to make the product even more attractive. As for some time now the AMP II has been recognised as one of the best power amplifiers available in the high-end scene, this has simultaneously become a challenge and an obligation. Therefore the question is asked: “What can one further improve with such a mature, good sounding product which has enjoyed success all around the world?”

AMP II: The world-wide award-winning champion

In recent years the model has been recognised with numerous awards in many international hi-fi magazines and many testers today refer to the device as a “reference”.  The claim is therefore fully justified that the AMP II is one of the world’s best output amplifiers in its class.

Here is an example from the press:
In its issue 12/2009, the German magazine “STEREO” rated the AMP II – MK 2 (the MK 2 is the former version of the latest MK 3) as a reference output stage and awarded the product the maximum points. At the same time it described the value for money as “outstanding”. “STEREO” wrote:

“…an output stage for high quality music, suitable for universal use and compatible to all loudspeakers. […] And clearly an inside tip for music lovers as this is the first time it has been possible to upgrade to the class of the top references for output stages for such a reasonable price.”

Finest electronic components – finest sound

The top priority in the development of the AMP II – MK 3 was a perfect signal feed with short distances using the finest components. Some of the components are individually selected as this is the only way to realise the perfect measurement values which form the basis for the breathtakingly beautiful sound of this dynamic amplifier.

The AMP II – MK 3 is a so-called “dual-mono power amplifier”, i.e. apart from the common mains cable both channels are completely separated from each other – from the transformer to the output stage board. This ensures the excellent values, for example, for channel separation and signal to noise ratio, etc. The high performance and simultaneously extremely low distortion in the AMP II – MK 2 is achieved using 2 x 1100 VA transformers, a filtering capacity of 160 000 µF, 24 selected MOSFET output transistors and much more. The result of this substantial oversizing is that even when working under high loads the components are never stretched to their limit of performance and therefore ensure the described excellent values. The AMP II – MK 3 works with Class A operation in most applications. And, despite its enormous power, the AMP II – MK 3 reproduces the finest details with extreme precision, in our opinion just as one would expect from a real reference product.

Impressive circuitry concept – excellent measurement values

The driver stage of the AMP II – MK 3 works on the principle of the current mirror. This circuit principle enables power to be drawn from an existing current. The AMP II – MK 3 is therefore a “power-controlled” output amplifier whereby the large number of MOSFET transistors ensure a very high current capacity without having to stretch the transistors to their performance limit. The AMP II – MK 3 is therefore also suitable for impedance critical or low-ohm loudspeaker systems. Ingenious circuitry removes the need for a servo controller for the “offset” and the quiescent current is generated via the IC or current mirror driver.  As a result, direct and alternating current errors (DC and music signal errors) are immediately corrected. This means the total offset is exclusively determined by the quality and symmetry of the used ICs.

The comment from the “STEREO” laboratory in the issue mentioned above was as follows:

“High and stable performance level, extremely low distortion, high damping factor, good noise values and band width with extremely high channel separation”.

Highest operational safety

Both output stage channels of the AMP II – MK 3 are equipped with a solid 12 kg heavy high performance heat sink which thanks to its special rib design serves to ensure a constant operating temperature of the MOSFET transistors. Even at full power there is no danger of overheating. An integrated control unit also permanently monitors operating conditions such as DC offset, temperature, clipping and high frequency. If a pre-defined value of one of these points is exceeded, the loudspeakers are immediately switched off to ensure the highest operational safety for the output amplifier and connected loudspeakers.

German engineering ingenuity

The AMP II – MK 3 is naturally “Handmade in Germany”. All manufacturing processes for this product, from the development through to final assembly, are made in Germany.

To conclude, we would like to quote “STEREO” once more:

Test result: “The amplifier is a model of stability and precision while at the same time versatile and agile, making the product a textbook example of how to build an amplifier. Homogeneous, universally usable, virtually perfect. And for this high-end product, an unbelievably reasonable price”.

AMP II - MK3 highlights

  • Dual-mono reference power amplifier with completely isolated power supply for each amplifier channel
  • 24 selected MOS-FET output transistors of finest quality
  • 2 magnetically shielded and encapsulated toroidal core transformers of premium quality for highest output reserves
  • Maximum total transformer power: 2,200 VA (watts)
  • Optimum smoothing thanks to 160,000 µF power supply capacity; Premium quality capacitors (“Made in Germany”)
  • Very high damping factor for perfect speaker control
  • ACCUSTIC ARTS® Damping factor linearization (switchable)
  • Professional protection circuit against clipping, HF oscillations and too high DC offset
  • Integrated switch-on current limitation for highest operational safety
  • Constant low operating temperature due to generously dimensioned heat sinks
  • Balanced input (XLR) and unbalanced input (RCA) – the inputs are switchable
  • All used components and parts are selected and of highest quality
  • Very high quality, gold-plated bi-wiring/bi-amping speaker terminal
  • Extremely stable, massive and resonance optimized housing, fully made of aluminium; inlay made of massive brass, polished and chromed
  • ACCUSTIC ARTS® AMP II – MK3 is “Handmade in Germany”

Specifications

Voltage gain:
31.0 dB

Total transformer power:
2 x 1.100 VA = 2,200 VA (watts)

Power supply capacity:
approx. 160,000 µF

Input impedance:
balanced (XLR): 2 x 20 kΩ
unbalanced (RCA): 100 kΩ

Rated power output (at THD+N = 0,1 %):
max. 2 x 675 watts on 2 Ω
max. 2 x 450 watts on 4 Ω
max. 2 x 275 watts on 8 Ω

Rise time/fall time:
3.1 µs with 4 Ω load (square-wave 20 kHz, 12 Vpp)

Crosstalk:
109 dB with 1 kHz

Signal-to-noise-ratio:
-103 dBA (ref. 6.325 V)

Intermodulation distortion:
0.007 % with 10 watts on 4 Ω

Distortion factor (THD+N):
0.001 % on 4 Ω load at 1 kHz and 10 watts

Dimensions (H x W x D):
350 x 482 x 430 mm / 13.8 x 19 x 16.9 inches

Weight:
approx. 55 kg / 121 lbs.