So, you need four units as a control section, a power supply section, and two of monaural amplifiers.
Arai: We were told to make the best products by the factory manager that time. The retail price of monaural amplifiers was 2 million Japanese yen each, or 4 million yen for two, and the PRA-S1 preamplifier was 1.5 million yen.
Does that mean that Denon had generously cultivated the technology by then?
Arai: Not only that, it was significant to introduce new technologies that had never been done before.
What was the new technology like?
Arai: First, the UHC-MOS (Ultra High Current-MOS) was the first circuit to be used in audio. This was a single element that could carry a large current. At the time our research department looked for various semiconductors while examining their characteristics with the development department, and in the end, we used industrial semiconductors.
Not for audio?
Arai: Back then, there were no audio elements that could produce the high current we were looking for. So the person in charge at that time, who also was my colleague, spent six months alone in a dormitory in Kawasaki looking for a high-capacity element that could be used for UHC-MOS and doing research on how to use it for audio.
So, he found it in industrial semiconductors?
Arai：Yes. But because it was not for audio, it was limited in practice. We had to do a lot of research to overcome these limitations and make it suitable for audio use. It was mainly a circuit design effort.
What other new technologies had been introduced in the S1?
Arai：The use of sand cast technology inside was also novel.
How was it used?
Arai：There was a sand casted chassis inside the golden aluminum plate, and the parts were placed there. By doing so, unnecessary vibration can be completely eliminated. However, the sand casting requires a certain amount of thickness, so the chassis inevitably becomes larger than a certain size.
There is a thick casting frame in the chassis.
Arai：Right. On a sand casted frame, the place where the panel and parts are attached is cut by machining to make a flat surface or to make a screw hole. This was also a method that was not possible with conventional audio equipment.