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Strumento No.4 mk2 Stereo Power Amplifier

Technical Data
Output power per channel Wrms 8/4/2 ohm 250/500/900
Gain 29 dB
Input sensitivity 1.41 Vrms
Frequency response (1W rms -3dB) 0,3 Hz ÷ 1 MHz
Slew-Rate (on 8 ohm) > 200 V/μS
THD < 0,05 %
S/N Ratio 110 dB
Input impedance Unbalanced 7,5 Kohm
Balanced 7,5 Kohm
Damping factor (on 8 ohm) > 1000
Main voltage AC (50-60Hz) 100, 110-115, 220-230, 240 V
Power consumption 3300 W MAX
Dimensions and weigth 450x280x500mm (wxhxd) - 95 Kg
Shipping dimensions and weigth 580x410x700mm (wxhxd) - 125 Kg

STRUMENTO n° 4 mk2 stereo power amplifier

The Strumento N°4 mk2 Stereo Power Amplifier is a close to perfection state of the art two channel power amplifier that exhibits incredible response speeds (bandwidth greater than 1MHz), high output power (up to 900 Watts), and nearly unlimited speaker driving/control capability. 
For the mk2 version we’ve used our experience in designing its sibling the Strumento N° 8 Mono-block Power Amplifier as well as our trained human ears to aide us to further refine the original Strumento N°4 circuit (such small, but critical changes include the value of resistors and capacitors). 
This effort has allowed us to more closely achieve our goal of sonic perfection with the Strumento N°4 mk2, much like a luthier uses years of experience, craftsmanship, and keen ear to find the perfect tonal character and emotional response for their instruments.

The Strumento N°4 mk2’s chassis begins its life as an ultra high grade, bespoke aluminum cast. After the CNC finishing work is completed, every part is then closely inspected and “mirror polished” by hand. Some critical areas are further finished by hand, with shot peening and anodization completing the beautiful metal work. The final touch is an elegant silk-screening process.

Within the beautiful casework of the Strumento N° 4 mk2 one finds yet more attention to detail and incredible Italian craftsmanship. There you will find a fully balanced circuitry, carefully selected ultra high grade components throughout, a massive power supply built with extra low impedance, 
ultra high grade capacitors (280.000µF alone on the main power supply), custom printed boards with an extra high-grade surface copper, and ultra pure copper bars in the output stages. But we have chosen to not stop there with the Strumento N° 4 mk2 Stereo Power Amplifier! The Strumento N° 4 mk2’s power supply is comprised of two super high current power supplies per channel and four stabilized independent stages for each channel: two for the input stages and two for the Audia Flight current feedback stage. The gain stage’s power supply is designed to achieve extremely low noise, the filter is made by ultra-fast rectifiers and extra low impedance capacitors. Two 150VA toroidal audio transformers are used for the main stages and one 15VA toroidal transformer is used for the logic control and protections. The main power supply is made by n.28 10.000µF 40V extra low impedance capacitors. No fuses are found in the main power supply for the output stage (we find fuses are like a “resistors” and can negatively impact the sound), instead a current sensor read by microprocessor is employed.

The amplifier’s gain stage is an exclusive Audia Flight design consisting of an entirely class A current-feedback circuitry. 
To further isolate this critical part of the amplification process from interference and grant thermal stabilization for all of its discrete components, the gain stage is enclosed within an aluminum box and encapsulated in an epoxy resin. Meanwhile, the output stage of the Strumento N°4 mk2 is powered by a massive 3000VA custom made audio transformer, encapsulated by epoxy resin and sealed within two ferromagnetic shields. 
Ultra-fast rectifiers instead of fuses are used on the main power supply for the output stage.

With every circuit detail addressed, we then turn to mechanical details to complete this masterpiece! When the amplifier is on a shelf, 
the power transformers, located on an independent chassis, are physically decoupled from the audio circuit chassis, thus discharging to ground any spurious vibrations from the transformers should they be present.

A masterpiece in aesthetics and electronics in a single chassis, the Strumento N°4 mk2 Stereo Power Amplifier is surpassed only by a pair of its sibling the Strumento N° 8 Mono-block Power Amplifier.