My private history of audio

Text: Shirokazu Yazaki
SPEC CORPORATION/Engineering
Dedicated to my friend, Mr. Wojciech Pacula

23 Apr 2013 16:55:09 +0900
Dear Wojtek!
For your information, SPEC will demonstrate a new heavy-duty turntable (a slightly higher price than the REQ-S1EX) at the Munich hi-end.
Yoshi Hontai/MuSon Project Inc.

23 Apr 2013 10:28:28 +0200
Yoshi!
It looks just fantastic!!!!
It seems that SPEC grows quickly like a weed :) Anyway, I decided to publish the story that Shirokazu Yazaki-san wrote about his career as the Editorial for the May issue of “High Fidelity”. It has never happened before in the nine years of history of our magazine for someone else than me to write the editorial. This way I would like to honour Mr. Yazaki and show my appreciation for everything he has so far achieved.
Best regards

Dear Wojtek,
Indeed, Mr. Yazaki of SPEC is a very interesting engineer. He loves the sound of 300B single-ended amp and has been continuously upgrading his 300B SE amp since 38 years ago, aiming for the ultimate sound. However, in order to solve the only disadvantage of 300B SE amp (not enough power to drive recent low-efficiency speakers), he finally reached to a solution to replace 300B output tubes by the newest and highest grade PWM switching devices supported by a pure analog power supply and West Cap type vintage oil capacitors. This means that 300B output tubes were just replaced by the digital amplification devices, but the basic theory is the same as a tube amp.
Although an ultimate target sound should be the same either by tube amps or solid state amps, the sound of these amplifiers is different at this stage. It means that both tube amps and solid state amps are still not perfect and it seems no more solutions for further improvements.
Some Japanese audio journalists commented that SPEC amplifier might be making the figure of the future of audio amplifier foresee.
Best regards,
Yoshi Hontani

PS
Spring is here finally!!!

20 February 2013

My authentic audio hobby started in 1971 when I just graduated from the university and entered the company named TEAC (at that time one of the famous tape recorder maker in the world) as a mechanical engineer. Because that I had been interested in the audio products, especially dynamic motion of open reel tape transport. But I suppose I was basically another music lover of Jazz and vocal Jazz.
Fortunately, as a Tube-Amplifier fan I was so excited because these fine European tubes were introduced into Japan in the early 1970 by Mr. Jean Hiraga. He started business importing mainly vintage British made tubes to Kobe in Japan. I was so stimulated from the articles of one’s own making tube amplifier mounted vintage European tubes on monthly specialized magazines, such as “MJ “or “Radio Engineering”. I had never heard the sound of such tube amplifier and only imagined a beautiful sound and look. But at last I could have the experience the sound and I was deeply impressed with the superb real-sound of single direct-heated power triode amplifier with the high efficiency horn speaker system ALTEC A-5 at the Audio-Fair 1971 in Tokyo. And this was exactly what spurred my own audio career.

I decided to start making a single power triode amplifier and collect a horn speaker system. First I started to build up the very simple “GEC DA30” (PX25A or CV 1178 British made power triode; these days DA30 is so rare that I suppose it’s only found in museum, even in the UK ) single ended amplifier with non-feedback circuitry according to the article in “MJ” June/1972 by Mr.Anzai and it was completed in early 1973. This amplifier is composed chiefly of Western Electric 310A as a driver tube, Telefunken GZ34 or Western Electric 274B as a rectifier and GEC DA30 as a power tube. The reason why I selected DA30 instead of the famous Western Electric 300B was that the higher frequency response of DA30 was wider and superior to WE300B in non-feedback circuit use. So my SE amplifier was composed of a US made driver tube and a British made power triode. It might be a rare case but I had never regretted this selection because of excellent circuit design thanks to Mr. Anzai. Already 40 years passed but every time I have heard the sound of DA30 driven by WE310A, I have felt natural, rich midrange, decent tonal-quality of British made tubes and also powerful mid-low range of special USA made tube. And curiously enough around 40 years after this very primitive tube amplifier I was led to the new generation D-class amplifier.

About the horn speaker system, first I got a pair of used vintage ALTEC 414A woofers in a nice condition at the end of 1973. It’s a 12-inch woofer but compared to the noted 15-inch 416A it has more high-speed mid to low range and I thought it might be better suited at home use. But I had a problem choosing the horn speaker between ALTEC, JBL and ONKEN. Finally I decided to have the ONKEN horn speaker system because of the exceptional flat frequency response and the organic, natural tonal character of the wood horn with amazing Japanese craftsman ship. First I ordered mid-high driver ONKEN OS-NEW500MT and SC-500WOOD horn in December 1973, but I received it in early 1975. It took so much time to produce the driver due to the craftsmanship of Mr. Koizumi aspiring for perfection. And in 1997 I got the OS-5000T Espit tweeter and the structure of my high efficiency speaker system was completed.

I also should say something about my “Marantz 7” preamplifier. In 1979 Marantz Japan released the kit form of “Marantz 7” as “Marantz 7K”. I had adored “Marantz 7” because of the legendary sound full of musicality and beautifully balanced design. So I built up the kit, but I used better quality parts than the attached parts, such as capacitors, resistors and so on. I learned so much know-how on how we can get a fine musical tonal character trough building up that kit. Of course I have made continuous sound quality improvements of my “Marantz 7” up to the present. That means, “Marantz 7” has been a good “professor of Audio technology” for me!

My professional career

I don’t have enough time to describe in detail my professional career of over 40 years. But I would like to mention of a few memorable product names that I have developed either on my own or as a manager or general manager of the engineering department. I worked in TEAC for about 4 years as a mechanical engineer designing open reel tape recorder and I think I learned everything about the technology of tape transport. I drew so many plans of mechanical parts for TEAC A-7300, high performance 2-track, 38 cm/sec semiprofessional tape recorder. And with this 4 years of experience I came to PIONEER and for the next 17 years I was in charge as a group leader or a manager in the engineering department of mainly cassette tape recorder. At that time I was already an expert of designing high performance “dual-capstan mechanism”. My interest and task was how to reduce the “wow & flutter”. And my team developed so many models in every year such as CT-A1, CT-A9, CT-91, CT-93 through 1980s but in 1992 we could release the ultimate cassette deck named PIONEER CT-95 (or T-1100S for the Japanese market). Combined with my “Reference Master Mechanism”, newly developed Dolby S system, precise automatic tape tuning system and so many improvements, CT-95 got the highest rating of German audio magazines. They said that CT-95 surpassed even the famous Nakamichi Dragon. It was my secret medal and delight.

And one more impressive model to mention is PIONEER DV-AX10. It was the world’s first real universal player, capable of playing CD, SACD, DVD, DVD-AUDIO discs. Not only the DVD video quality was remarkable but also the CD sound was full of musicality. DV-AX10 got the gold medal of HiVi (Monthly Japanese magazine) among all of the 1999 audio-video products in Japan. As a general manager of DVD engineering department I could feel delight and honor. And I met one fabulous engineer, Mr. Banno who struggled to manage the engineering team of about 40 people as the manager and looked for a breakthrough in a range of hard developing issues. And would you believe that after 10 years Mr. Banno and I are every day in hot pursuit of a nice sounding D-class amplifier in SPEC corp. He and I could experience so many types of sound during these developing stages of AX10 and it also seems those experiences led to the development of D-class Amplifier.

How I was led to D-class amplifier

Around the end of 1990s and the beginning of 2000s PIONEER corp. reached its full bloom. So we could have the rare chance to develop a high-end DVD player such as AX10. Also we had a well-designed, spacious listening room and could select high-priced speakers, pre-amplifier and power amplifier as the reference at that age for our development of AX10. I remember that I got B&W801, it was the standard or the reference of specialist audio shops in our domestic market. Of course B&W801 were driven by high power semiconductor amplifiers of famous domestic and foreign brand. But I and also Mr. Banno had never been moved by the sound of this high-end audio system. The sound looked like watching miniature paintings, we could hear out all the details but could never be touched by this music. We felt the sound, very precise but one-dimensional and lacking any dynamic or rhythm. But when I came back home and listened to the music on my old high efficiency system, I was intoxicated by the music playback. So transparent, so natural and just like organic sound. I felt the difference of the sound came from the distinction of some dynamic characteristic of two systems not only from static one. But I couldn’t understand clearly the reason why at that time.
It was unexpected but my career in the engineering department was over in the spring of 2000 and I was transferred to work in a subsidiary production company at Semarang/Indonesia for management reconstruction as President Director. So I should have to depart far away from the sound of my old system. And I could experience so many hardships about all the aspects of my life in an equatorial foreign country and I think those hardships in unfamiliar circumstances or the nature of rainforest had fostered my some inner strength and musical hearing ability. But Indonesia has become my second home province right now.

Coming back to Japan I was put in charge of research and development center at the end of my career in PIONEER. So I could choose a good sound system with an amplifier and speakers by myself for the job. It remains in my memory that one day in October 2006 I had a chance to hear the demonstration of new D-class amplifier devices and the prototype amplifier those devices were used. I was very impressed by the sound, it was only a prototype so the sound was not sophisticated but rich mid to low range made it feel like a good tube amplifier with similar musicality in it. I felt obviously the differences from the sound of a traditional semiconductor amplifier. On December 9th, 2006, on another business trip I had a chance to talk to the person who developed the amplifier in Los Angeles, California. As a matter of fact, he was my junior colleague from PIONEER corp. and also privately a good friend in terms of audio. Mr. Honda emigrated to USA with his family and found a job in “International Rectifier”, semiconductor manufacturer specializing in power management called IR. After around 6 years working in IR, he just developed newly D-class devices. I felt he was not only a nice guy but also an excellent engineer with some genius for the audio circuitry so a dinner with him at a seaside restaurant was a full delight. We talked about our private life and of course about audio, especially his newly developed devices. It was a great night for us and factually this meeting with him was the start of my searching for the musical sound from the brilliant IR D-class devices. And not long after that we started our new company, “SPEC CORPORATION”, on February 6th, 2010.

I already had a lot of know-how on how to break in those devices to improve musicality. There are two major points: one is the low-pass filter in the final stage of D-class amplifier and the other major point is the quality of the power supply. But today I would like to mention about the low-pass filer. The role of this filter is very important for the switching amplifier, because it filters out the PWM switching career about 400 kHz in an efficient manner and it passes along pure analog signal current to the speaker. This circuitry is so simple, it is composed of a single inductor and single capacitor, but the quality of the analog current, in other words the sound quality depends mainly on the quality of those two parts. And I should say that the switching ability of IR D-class amplifier devices is nearly mostly perfect. IR states that the efficiency of the power transformed to the speaker reaches 96% at maximum power. Yes, we got the new generation audio power handling devices! And I believe firmly that these facts should be a good news for music lovers in the world.

I would like to go back to my story about low pass filter. At the end of 2009 I had reached a conclusion that best capacitor to use in this filter was the vintage oil-filled capacitor or “Hermetic-seal” marking with WEST CAP, CPV09 0.47/600 made for US military use in 1967. Of course, used as a coupling capacitor it also improved remarkably the sound of my old DA30 non-feedback SE amplifier. In a word, the sound gained musicality, deep bass with no trace of grain in mid to high range. But we couldn’t use these NOS parts for our new D-class amplifier. It was hard to find a solution for this problem, so hard that I can only explain the ensuing fact as God’s intervention. It turned out that the capacitor manufacturer has survived in Tucson, Arizona, USA. It changed its name from “West Cap” to “Arizona Capacitors, Inc.” in early 1990s. Arizona Capacitors took over from West Cap huge quantities of production facilities and engineering drawings. Our company has been working together with Arizona Capacitors as their distributor in Japan, selling quality custom oil-filled capacitors from the summer of 2011. Japanese old tube amplifier fans remember the name of lovely sounding old vintage “Sprague” and “West Cap” capacitors. Our distributing business has been growing because of the high tonal quality of these oil-filled capacitors. We were able to adopt custom oil-filled capacitors for all of our amplifiers, that’s it. I feel a miracle happened to me. Special thanks to Lord that I have been blessed so many times by coming across such high tonal quality parts!

If I were to say something about the excellence of D-class amplifiers I would say that it is important how they control the inevitable back electromotive force (BEMF) from the speaker. In D-class amplifier the current of back electromotive force is directed back to power supply but in a traditional solid state amplifier the current enters forcibly into the feedback circuit. That disturbs precise phase transmission of dynamic music signals. That is the reason why our RSP-101 improves the sound and it helps protect precise amplifier circuits, especially solid state amplifiers with the deep feedback circuit.

Thank you for giving me the chance to share my experience!