The latest member of our reference series:
ACCUSTIC ARTS® TUBE-PREAMP II

World premiere! At the end of 2009 the time had come. The ACCUSTIC ARTS® TUBE-PREAMP II celebrated its world premiere. The TUBE-PREAMP II is a further addition to our ACCUSTIC ARTS® Reference Series and perfectly complements the existing products of this series which have enjoyed worldwide success and received a number of awards. The TUBE-PREAMP II is the perfect playing partner for the reference power amplifiers AMP II – MK 2 or AMP III.

Clever: The circuitry

The ACCUSTIC ARTS® TUBE-PREAMP II is a preamplifier with an exceptional and uncompromising design along the lines of the so-called tube-hybrid concept. This concept, also an integral part of our TUBE-DAC II, combines the advantages of transistor technology with the advantages of the tube principle. Tubes are excellent voltage amplifiers, but can only supply a limited amount of current. As a result, in the TUBE-PREAMP II we place the tubes exactly there where these clear advantages can influence the acoustic pattern, i.e. for the voltage amplification. In places where current has to be supplied, e.g. for impedance conversion, we use the proven premium IC OPA627® from Burr Brown / Texas Instruments. This combination allows us to achieve very low-resistance outputs which are also characterised by a high current capability. We use solid state technology and tubes to take advantage of their physical characteristics to realise an exceptional, analogue sound experience with an extremely low harmonic distortion and excellent harmonic distortion spectrum which sets standards.

As opposed to most tube preamplifiers, the TUBE-PREAMP II is in fact fully balanced, i.e. with 4 completely separate amplification stages from the signal input to the signal output. This proven principle of fully balanced signal processing was taken over from our PREAMP I – MK 3 preamplifier which has been successful for a number of years and further developed to meet new requirements.

The 4 amplification stages are divided into one inverting and one non-inverting signal path per channel. Each of these amplification stages contains a high precision tube manufactured according to military specifications. This principle enables perfect channel separation.

The loudness is adjusted via a high-end selective, high precision 4 channel potentiometer. It is natural that the TUBE-PREAMP II functions completely according to the proven Class A principle.

Elaborate: The power supply

An ideal power supply is a precondition for a high-end preamplifier. The requirements for the power supply with a tube-hybrid preamplifier are much higher than for a purely transistor-based device. This is because the tubes require different low voltages and also a high voltage of approx. 300 V for the anodes. This high voltage has to be precisely controlled and absolutely free of interference so that the music signal can be perfectly amplified in the tubes. For this reason the TUBE-PREAMP II is equipped with a number of separately functioning power supply units and 2 separate high-end transformers, with one transformer exclusively reserved for the voltage required for the tubes. Both the toroidal core transformers used in the TUBE-PREAMP II are of an exceptionally high quality and have the best possible core material from Switzerland in order to prevent any negative interference inside the unit. In order to ensure that the power supply units work perfectly, the filter capacity for all voltage circuits was selected generously (e.g. 20,000 µF alone for the voltage supply to the semiconductors).

Perfect: The tubes

There is no dispute that the quality of the tubes is decisive for the quality of a unit based on tube technology. Tubes are sensitive components and thus have to be carefully selected and tested. We manually select the tubes and make pairs according to strict testing and measuring criteria to ensure that only perfect tubes are used in the TUBE-PREAMP II. Before the tubes are fitted to a TUBE PREAMP II, they have already passed a two-stage inspection process: one inspection carried out by our supplier and a second inspection made by our own specialists.

Before and after the first continuous test of 100 hours, all functions and parameters of the whole unit are inspected and recorded in a protocol. The values are compared and if the deviations are within a defined low tolerance range the unit is subjected to a further second continuous test of 100 hours. After this test further measurements are made and here the parameters must fit perfectly with the output values. In total, a TUBE-PREAMP II is measured and tested three times and the tubes are even tested four times. The TUBE-PREAMP II only leaves the premises of ACCUSTIC ARTS® after the requirements have been 100% met. This high level of scrutiny guarantees an extremely low failure rate of the tubes and ensures many years of uninterrupted musical pleasure.

The type of tube used is a so-called dual triode tube type E83CC in the special version 7025 and belongs to the tube group 12AX7. The tubes meet the high requirements of the military and come from the current production of a European manufacturer. The sound can be described as: pleasantly warm with a very balanced sound pattern, a sophisticated bass range, clear high frequencies, good dynamics and low harmonic distortion.

We prefer tubes from the current production and do not use NOS tubes, as these are not available in sufficient quantity and not available in consistent quality.

Quality: The rest of the components

The TUBE-PREAMP II guarantees absolute perfection through the exclusive use of selected components with low tolerances and highest quality grade. A number of the individual components are re-measured by hand and sorted into matching pairs.

The housing is also uncompromising: solid, carefully crafted aluminium plates combined with chrome-plated rotary parts in brass allow for a high quality look and surface feel and excellent stability. Stability is important to ensure that the tubes can work undisturbed and are not compromised by any vibration present in the housing.

Simple: Operation

As with all ACCUSTIC ARTS® products, the TUBE-PREAMP II is also easy to operate. This is a welcome change for many music lovers today when most electronic devices are overloaded with partly unnecessary functions.

The basic functions of the TUBE-PREAMP II are operated by two chrome-plated rotary controls. Both controls are more or less built to last for ever. The rotary controls, for example, are solid and are equipped with gold-plated contacts, which are corrosion-resistant and also enable many thousands of switching cycles.

Phenomenal: The sound experience

The result of top quality individual components, detailed development work, innumerable sound tests, careful production and involved measurement tests is a sound experience of the highest perfection.

In combination with the other reference series products of ACCUSTIC ARTS®, music is transformed into an incomparable sound experience "Handmade in Germany".

TUBE-PREAMP II highlights

Audiophile reference preamplifier with a so called "tube hybrid"≠ concept and 4 military tubes (2 tubes per channel)

Fully balanced circuit design from input to output

Advantages of this "tube hybrid" technology:
- very high bandwidth
- very low distortion factors and a "good-natured" distortion spectrum
- "analog" and very precise sound performance
- 4 separated amplification paths, which are not influencing each other

Easy change of tubes without any adjustments just "plug and play"

Professional Class A output stage using technology derived from studio engineering

All used components are of outstanding quality (e.g. Burr Brown® OPA 627) and additionally selected; all relays have high quality gold-plated contacts

4 high precision military tubes; 4-times selected

Premium quality rotary switch with gold-plated contacts for input selection

4-channel volume potentiometer for best crosstalk

2 magnetically shielded, encapsulated 75 VA toroidal core transformer ("Made in Germany") of premium quality for high output reserves

3 x fully balanced high level inputs (XLR) and 2 x unbalanced high level inputs (RCA)

2 x fully balanced outputs (XLR) e.g. for Bi-Amping configurations and 1 x unbalanced output (RCA) e.g for a separate active subwoofer or an unbalanced working power amplifier

Front panel, top cover and remote control made of massive and solid aluminium; turning knobs made of massive and chromed brass