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BlockAudio Line & Power Block and Mono Block

02.09.2017 // Dirk Sommer and Roland Dietl

Through the cable connections the Monoblocks report the temperature of the power transistors at the preamplifier where they are then shown on the display. In my relatively small listening room the temperatures easily reach 60°C, and if the windows are closed and the room temperature increases they can possibly be a couple of degrees more. Thus, the Class-A bolides ‘heat’ a little more than Einstein's OTLs. Good, that I deal with the OTLs and Class-A-Monos before it gets really warm outside. However, those who can afford a pair of the likewise fantastic and tonal slightly different Einsteins or BlockAudios, most likely will also have a larger and thus airy listening room than mine is… However, before I start sharing my experiences from the listening room, it will not harm you to get a little more information about the techology of the BlockAudio. But you won’t get this from me, neither as an audio-file to listen to straight from he developer as in the review of the Kawero!. Holding an interview, including editing on the Digital-Audio Workstation is even more labour intensive than writing about it. My colleague Roland Dietl, who is more than skilful in the area of circuit technology, has kindly offered to take over this task, leaving me with a little more time to prepare for the High End show:

The capacitors for the power supply of the input stage and drivers
The capacitors for the power supply of the input stage and drivers

„I had the chance for a detailed talk over FaceTime with Jiri Nemec on the technical concept behind the devices and the solution approaches he used. These are not entirely new however, but captivate through uncompromising implementation to the smallest detail, and give a good impression of what is really important. Let’s start with the mono power amplifier, which impressively demonstrates what real Class-A operation at 200 Watt output power into 8 Ohms actually means – respectively a huge power dissipation of 500 Watt in idle operation (!), which leads to enormous heat development that has to be deducted through large heat sinks at both sides of the device. For such capability a suitable power supply is needed first. Jiri Nemec likes to compare the power supply of the power amplifier with the engine size of a car, as it is commonly known that there is nothing to replace this. Following this philosophy, a massive 2,500 Watt toroidal transformer can be found at the power amplifier, which even at maximal output power into 2 Ohms is 2 to 2.5 times over-dimensioned. The filtering of the rectified AC voltage for the power part is done by eight high performance capacitors with a capacity of 47,000 μF each. For the voltage supply of the small signal parts there are further power supplies and filtering capacities resulting in availability of an overall capacity of around 0.5 Farad. With the mostly constant current output due to Class-A operation, the power supply should behave like a regulated voltage supply.

Attention to detail: BlockAudio device feet with steel ball and Widia base plate in the interior
Attention to detail: BlockAudio device feet with steel ball and Widia base plate in the interior

The rectifier diodes are connected to the heat sink through heat pipes. Jiri Nemec has kept the audio circuitry itself relatively simple. It is a fully discrete construction, DC coupled, has a DC-Servo that regulates DC residues and does not need capacitors in the signal path. Jiri Nemec works with a quite strong feedback, without which it would not be possible to reach the enormously high damping factor of 5,000. At the input stage there is a differential amplifier with JFETs and the subsequent voltage amplifier stage is built with a combination of MOSFETs and bipolar transistors. In the output stage on each of the two heat sinks work 8 bipolar, 200 Watt power transistors from Sanken. Here, it is a little unusual that only strictly selected NPN types are used instead of the usual complementary transistors. This is a conscious decision of the designer and is one of the reasons for the outstanding Monoblock sound.


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