Inside Denon

110TH Anniversary of Denon Vol.3 Interview With Takashi Arai, Amplifier Engineer

Denon is celebrating its 110th anniversary in 2020. Seizing the opportunity to celebrate this milestone, we are publishing a series of articles on Denon's history, its sound philosophy, craftsmanship mindset, notable products, and interviews with key people on our official blog. In this third article, we talked to Takashi Arai, who has been involved in the engineering of Denon amplifiers since the 1990s.

Denon Staff

Denon’s Power Amplifier History Goes Back to the Days of the Electric Gramophone

We've interviewed Mr. Arai many times for the Denon Official Blog about Hi-Fi amplifiers. Since it is the 110th anniversary of Denon, I would like to ask you about the history of Denon, focusing on its power amplifiers. Does Denon have a long history of amplifiers?

Arai: Well, the first part of the 110 years of the history is all about the gramophone. However, since the gramophone uses electricity—initially called electric gramophone—there was already an amplifier developed because of the need for electrical amplification in those products.

When did you first become aware of Denon amplifiers?

Arai: When I was in high school, I fell in love with audio equipment. At that time, Denon had the PMA-950 and PMA-970 integrated amplifiers, and I admired them a lot. Of course there were more expensive independent amplifiers too. To me, a separate amplifier was just a dream, and I didn't allow myself to think I’d even want one, but I thought I could buy a PMA-950 if I worked part-time while I was a university student.

PMA-980 Integrated amplifier (Denon Museum)

You joined Denon after graduation, didn't you?

Arai: Yes, I joined the company in 1986. At first, I was assigned to professional equipment, engineering displays for personal computers and CD players for DJs. In 1994 I was transferred to the amplifier development section. The first amplifier I worked on was a karaoke amplifier.

Ideal Quality Sound on the Best Technology

"S1" is the origin of Denon amplifier

When did you first get involved with Hi-Fi amplifiers?

Arai: I started working on consumer-oriented Hi-Fi amplifiers around 1995. I've been involved with Hi-Fi amplifiers ever since, and I've been engineering for 25 years now.

What was the reputation of Denon's amplifiers when you started engineering Hi-Fi amplifiers in the 1990s?

Arai: Back then Hi-Fi amplifiers sold reasonably well overseas, but they were not sold at all here in Japan. The domestic market share was dominated by several other companies. This situation prompted Denon to start releasing the new top-of-the-line S1 series around 1993.

What is the S1 series?

Arai: S1 stands for "Sensitive One," which means "something that appeals to the senses.” The S1 series was a series of products that attempted to create the best possible product by cumulating technologies. I think it was partly due to the economic bubble at the time that we were able to develop the S1 series with the aim of creating the absolute best possible product at that time. It also included both a CD player and an amplifier. I may also add that the power amplifier was too heavy for one to carry.

An amplifier that cannot be carried by one person. What do you mean by that?

Arai: Yes, it was a monaural amplifier called the POA-S1, and single one weighed 79 kg (~175 lb.). I even bought a special cart with a hydraulic jack to raise it to the height of the desk for development and sound quality studies.

By monaural amplifier, do you mean you needed two of POA-S1s for stereo playback?

Arai: Yes, that is right. Moreover, PRA-S1 was a preamplifier with a balanced configuration with a two-chassis structure in which the control unit and the power supply unit were independent from each other.

The stereo preamplifier PRA-S1 on the top left row (Denon Museum)

So, you need four units as a control section, a power supply section, and two of monaural amplifiers.


That’s amazing.

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.

Catalog of POA-S1 monaural power amplifier

So many “firsts.” Do you consider the S1 series as the most impactful update in Denon’s 110-year amplifier history?

Arai: Yes, I think it is an essential product in the history of Denon amplifiers.

I see that many of the technologies first used in the S1 became breakthroughs and are still in use today as a part of Denon amplifier tradition.

Arai: I think it is fair to say that the UHC-MOS, the core of Denon amplifiers, and all-stage balanced amplifiers are the roots of today's Denon amplifiers.

What are the sound features of the Denon amplifier?

Arai: What I consistently say is "subtlety and strength at the same time.” This is a feature of UHC-MOS.

Is this possible because UHC-MOS is capable of instantaneous high-capacity current flow?

Arai: The "power" part is true, and the single push-pull circuit allows the signal to be amplified at a single point, which contributes to the "subtlety" of the sound.

So, this S1 is the origin of the Denon integrated amplifier.

Arai: That's totally right.

Model Changes of the PMA-2000 Series for a Quarter of a Century

What are some of the most memorable products you made over the years in the field of Denon amplifier engineering?

Arai: One of the models I worked on that is still in the series is the PMA-2000. The current regular model is PMA-2500NE, which already has a part number that exceeds 2000. The PMA-2000 series lasted for seven generations, followed by the current PMA-2500NE. So I guess it’s actually eight generations. Now, as it is our 110th anniversary, I wanted the PMA-A110 Anniversary Edition to be an adventurous model worthy of a commemorative product.

The PMA-2000 series has been through model changes for a quarter of a century, but which model is particularly most impressive to you?

Arai: The first generation. Up until then Denon amplifiers didn’t sell well in Japan. So when we were developing the PMA-2000, we changed the development process of the previous amplifiers and made them entirely new.

Integrated amplifier PMA-2000 (Denon Museum)

Were you determined to change Denon's amplifiers?

Arai: Yes, we were. That is why we engineered them with the goal of outperforming the amplifiers of other companies that sold well at the time.

That sounds like a lot of technical work.

Arai: I tried to improve the amplifier not only in terms of technologies such as output and distortion, but also in terms of its appeal as a product. That is why we put effort into creating a powerful amplifier, which ended up making it bigger and heavier. Denon’s previous amplifiers were small and light weight compared to those in the same price range. Size was an important factor in audio equipment at that time. One of the critics in those days weighed everything on a scale and used it in their evaluation criteria.

What other innovations did you make?

Arai: We used UHC-MOS, which was highly evaluated in the S1. The PMA-2000 was a model with the cost of 100,000 Japanese yen, so we had to find another element that was cost-competitive and could carry a large current.

That's more tough work.

Arai: It was not only difficult, but also caused unexpected problems. I found a good element earlier. I used it to make prototypes and conduct tests, but then the device suddenly became unavailable for sale. I was very surprised. So, we went back to the drawing board to find another element, and eventually we managed to find a solution.

We wanted to compete in the same retail price range as our rivals, so the price was set at 100,000 Japanese yen, but from a profit standpoint, we were supposed to sell it for 140,000 to 150,000 Japanese yen. The cost of materials was so high that we could not make a profit out of it. That's why the section manager said, "If we cannot be successful in this model, we'll stop making amplifiers all together.”

But the PMA-2000 was a big hit after all.

Arai: Yes. It was greeted with great interest by many audiophiles and was ultimately a hit. It became a long-selling series that continues today. I still use it as an example of excellent construction, and I have not changed a single part of the molds I made for the PMA-2000.

That's how perfect it was. What was the reason the PMA-2000 became a hit?

Arai: I think achieving the "combination of subtlety and power" that Denon is known for in the S1 was highly valued with the retail price of 100,000 Japanese yen. The PMA-2500NE is the backbone of Denon’s amplifier lineup, so I think it is fair to say the PMA-2500NE is the embodiment of Denon's sound. This culminates in the new limited PMA-A110 model, which even houses technologies that previously where only applied in the flagship SX series only available in Japan.

The Function of the Amplifier is Simple. But the Requirement Changes Depending on Components to Be Connected

How do you see the evolution of Denon's amplifiers in the future?

Arai: The function of an amplifier is simple: to increase the incoming audio signal and to make an expanded copy. We will not change the ability to reproduce music accurately, that’s for sure. I also believe Denon amplifier’s "subtlety and power" characteristics and the company’s new sound philosophy of "Vivid and Spacious" will carry us into the future.

However, the amplifier does not produce sound itself. Music is only played back when it receives a signal from a player, the source of a sound, and passes it onto speakers that produce sound. That is why I think the required capabilities will change as the connection partner changes.

For example, large speakers that were once commonly used, such as a 38cm (~15-inch) woofer, are not used much these days, so there are fewer cases that require large amounts of instantaneous power on the amplifier side. On the other hand, sound sources like SACD and high-resolution sound sources have increased, as well as the number of higher-density sound sources. As a result, amplifiers are required to be able to accurately amplify more delicate and detailed sounds. I believe that amplifiers will evolve in this direction in the future.

Find out more about Denon 110 year legacy in audio here.

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