But let’s now go back to the Mono II, the second-largest amplifier in the Swabian’s reference line, which I have chosen because its opulent output power range of 300 watts at eight and 500 watts at four ohms is being more than enough for my system’s requirements. However, in contrast to the 60 kilograms of the top model Mono III, the Mono II only weighs “amicable” 25 kilograms. The discussion with the designer revealed that the Mono II despite its XLR input is not a balanced amplifier in its own right. If one selects the balanced input, the audio signal is converted into an un-balanced signal using an IC from Burr Brown and then treated in the same way like the signal entering the power amp through the RCA input. One could now begin to hotly dispute whether it would be better to lead the signal through the RCA output of Einstein's fully balanced The Preamp, thereby bypassing AccusticArts’ un-balancing circuitry or benefiting from the less susceptible balanced signal routing on the six meters long cables between pre and power amplifiers. Since there were no un-balanced signal cables around that could match the quality of my XLR connections, I will excuse myself from further musings on the matter, leaving everything the way it was by simply replacing Einstein’s The Poweramp with the two Accustic Arts Mono II.

After having passed the RCA input respectively the un-balancing circuitry, the signal is fed into a Burr Brown class A current amplifier. As Accustic Arts’ electronics designer explains, this is an extremely linear class A current mirror driver stage using six characteristic curve selected high-frequency transistors, which at the same time defines the relatively high bias current and the DC zero point for the twelve MOSFET power transistors selected in the same way. The power amp produces an astonishingly small percentage of distortion. In addition, 99% of the distortion spectrum consists of K2, aka harmonic distortion, which the ear perceives as pleasant. For the protection circuit, he defined a specific frequency curve in order to make a DC avoiding servo circuit at the output obsolete. Capacitors in the signal path he omitted as well. The capacitors next to the signal path are FKPs or polypropylene foil capacitors from Wima with a maximum tolerance of one percent. Except for the source and Boucherot resistors, only metal film resistors with a tolerance of one percent are used. Regarding the Boucherot resistors only metal oxide layer types with low inductivity and also a maximum deviation from the nominal value of one percent are allowed. All source resistors come up as low-inductance metal-band versions with ceramic housings.

A considerable effort is also applied to the power supply. The 1,200 VA toroidal mains transformer is manufactured according to Accustic Arts’ specifications and shows an additional copper band winding for statical screening, a potted structure, a MU metal magnetic shielding, and has separate windings for the positive and negative supply voltages for the MOSFET output stage, as well as for the input and driver stages. Their share of the total capacity of more than 80,000 microfarads is multiplied by a newly developed capacitance multiplier circuit similar to a gyrator. Ultra-fast switching diodes are used for rectifying both voltages. Although the Mono IIs admittedly have a high damping factor, it isn’t the absolute value – this is varying between 400 and 1000, depending on the measurement method – that’s got the highest priority for their developer, but more the fact that the damping factor stays linear beyond the audible range. This makes the work for the connected loudspeakers a lot easier.