Features:

• Linear integrated amplifier
• Combines advantages of tube and transistor amplifiers
• 0 Ohm Input impedance at output
• Damping factor virtually infinitely high
• Output signal 100% part of negative feedback control
• Controls loudspeaker including cables and connectors
• Loudspeaker properties are idealized
• No post-pulse oscillations of membrane
• Stereo/Mono switchable
• ALPS Precision-potentiometer
• Extremely high efficiency
• Protection circuit protects loudspeaker and amplifier
• Suppression of noise at power switch-on without loudspeaker relay
• Stable aluminum chassis
• Front panel available in black or silver
• Available as “Powered Edition” with larger power supply (at additional charge)
• Comes with power cord and user manual

A perfect combination at a moderate price: The ABACUS 60-120C linear integrated amplifier and the ABACUS 6-2RC Preamplifier.

The amplifier

Similar to tube amplifiers, the ABACUS amplifier uses the collector (in tube amplifiers: anode) of the output transistors to drive the loudspeaker, instead of using the emitter (in tube amplifiers: cathode) as done in common audio amplifiers. The advantage of using the collector is that it is always able to provide the maximum current, independent of the instantaneous value of the voltage. Hence, ABACUS amplifiers operate independent of the load.

The difference to tube amplifiers is that ABACUS amplifiers do not use an output transformer. Furthermore, ABACUS amplifiers provide 100% negative feedback and the output impedance is exactly zero. From this follows that with ABACUS amplifiers, the loudspeaker is not simply excited, but guided in a controlled manner.

Both amplifier channels feature a unique safety fuse. In the event of a too high current, the amplifier section is switched off, protecting both the loudspeaker and the amplifier. As soon as the current has again dropped below the necessary limit, the amplifier section is switched on again and continues to work.

The input stage

The input of the ABACUS 60-120C is equipped with gold-plated RCA sockets. A switch allows to choose one out of three available operation modes: Stereo, L+R and mono.

In stereo mode, both channels are fully independent of each other. The L+R mode uses the same input signal on both channels and therefore allows the operation, e.g. of a two-way loudspeaker, where each amplifier channel is dedicated to either the woofer or the tweeter in the loudspeaker in question. If switched to “Mono” both amplifier stages are in bridge mode, i.e. the output voltage is doubled (up to 144 V peak to peak). This is desirable whenever high power is demanded, e.g. in high-impedance drivers, etc.

The ABACUS 60-120C is able to work as a true mono block. The input stage is completely active and therefore immune to all kinds of parasitic drag.

Volume control

It can be questioned whether a power amplifier requires a volume control. However, being able to adjust the input sensitivity is essential. Therefore the ABACUS 60-120C features a volume control potentiometer which gives full control over the input sensitivity. In this way, the ABACUS 60-120C, being a linear integrated amplifier, can be used without a preamplifier, if only one audio source is needed.

ABACUS uses the ALPS precision potentiometer RK 27 as the volume control. Since it is not working within the signal path but only controls the amplification, it does not have any influence on the sound quality. In combination with a preamplifier, the ABACUS 60-120C acts solely as a power amplifier, the potentiometer is used for the level adjustment only and is usually set to 12-o'clock.

The power supply

Any amplifier can only provide the amount energy, taken before from the mains supply. Therefore the interaction between power transformer and the electrolytic capacitors determine the power capabilities of the amplifier.

This important fact can also be illustrated by considering a bagpipe player: The bagpipe player's lung, pushing a constant amount of air into the bagpipe, represents the power transformer, while the bag itself represents the capacitors, acting as a buffer for the air (or electric energy in amplifiers). The energy for fast and strong signals stems from the capacitors. However, the transformer has to be large enough, in order to fill the capacitors again with energy. A high peak power requires a high capacity while a strong transformer is required for a high continuous power rating.

The ABACUS 60-120C is available in two versions. The standard version is equipped with a 160 W transformer and 30000µF charge capacity. The stronger “Powered Edition” possesses a 225 W transformer and a charge capacity of 40000µF.

A simple illustration: The energy in the capacitors in the “Powered Edition” of the ABACUS 60-120C can move 1 kg to a height of almost 2.5 m.

The loudspeaker terminals

Isolated and gold-plated loudspeaker connectors offer a stable connection for banana connectors as well as plane thick wires. The switch-on-noise suppression operates without any kind of relay, leaving nothing but the cable and connectors between output transistors and the loudspeaker.

Note that the loudspeaker cable as well as the connector is integrated in the negative feedback. In this way, the cable does not have to be of any superior (and expensive) quality; only the cross-section is important.

Specifications: