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A Guest Article from Mr. Shirokazu Yazaki: “My Adventure With My Old Marantz Model 7” Part 5!

06-25-2017 | By Jeff Day |

It has been my great pleasure to bring you posts from Yazaki-san for his article “My Adventure With My Old Marantz Model 7”.

Yazaki-san's vintage Marantz 7k preamplifier.

Thank you, Yazaki-san, for taking time to write this article and share your substantial audio wisdom with us, it is very much appreciated by me, as well as all of us here at Jeff’s Place!


In Part 1 Yazaki-san told us about his near forty year passion of pursuing ‘real sound’ with his vintage Marantz Model 7 preamplifier, and the resulting enjoyment & satisfaction that pursuit has brought to his life.

Yazaki-san shared with us his thoughts about several brilliant design aspects of the Marantz Model 7, and how its design allows it to still hold its own against, or even surpass, anything made today in musical ‘real sound’ terms.

Yazaki-san also told us about his approach for fine-tuning the Model 7’s performance for ‘real sound’ through a careful selection of internal parts like capacitors and resistors, and finally, hinted at the modifications he was going to tell us about in Part 2 of his article that would take the Model 7’s performance to an even higher level.


In Part 2 Yazaki-san told us about his way of modification with his Marantz Model 7, and how important the quality of the power supply is to the overall performance, because the current from the power supply turns into the signal current.

Yazaki-san described for us how the switch to the Ultra-Fast & Soft Recovery STTH6112TV2 for +B rectification improved the speed of the current from the power supply, and lowered the noise.

Yazaki-san also described for us how he likes to install a hermetically sealed oil-filled capacitor into the subsequent stage of the rectifier tube or diode, connected in parallel with the main electrolytic capacitor for rectification, and how that its addition provides a more responsive and organic sound.


In Part 3 Yazaki-san told us about his discovery of how the addition of a decoupling capacitor for the +B voltage line (280 VDC for V3 and V6) of the cathode follower in the Marantz Model 7, brought about such an important improvement to the sound quality.

Yazaki-san also described how he brought out the full potential of π filters in his system by using Ohmite Brown Devil resistors in place of the original Allen Bradley resistors used in the Model 7, and shared with us his perceptions of how the inductance of various wattage ratings affected the overall tonality and voicing.


In Part 4 Yazaki-san told us how he learned about the use of mica capacitors in tube amplification circuits, more than 35 years ago now, in the MJ special edition book (1971) of Isamu Asano-san, “The Fascinating Tube Amplifier, Its History, Design and Assembly”.

Yazaki-san was impressed with the clarity and high-resolution of the high-frequencies with the NOS mica capacitors he tried, and how their mid-range had beautiful tone that was full of information, and how their overall sonic performance was full of exactness and elegance.

Yazaki-san attributed much of the excellent performance of these NOS mica capacitors them being fully free from inductance compared to any of the tubular style of capacitors.

Yazaki-san told us about when he installed NOS mica capacitors into his DA30 SET amplifier as coupling capacitors, the improvement in performance that resulted, and recommended we also try a mica coupling capacitor adventure of our own in our tube amplifiers to get a sense of what he experienced.

Yazaki-san told us about how his passion for the transparent performance of mica capacitors led him to develop and produce the Spec Corporation MC-DA series of ruby mica capacitors specifically for high-performance audio use in his own Spec products, and how Spec now also makes them available to the DIY community.

Yazaki-san went on to tell us about his use of the Spec ruby mica capacitors in his vintage Marantz Model 7 preamplifier as coupling capacitors, and they dramatically improved the sound quality, and brought out "an information rich sound" from his Model 7.


Now, without further ado, let me introduce you to Yazaki-san’s Part 5 of his article, where he continues to discuss his method of modifications to his vintage Marantz Model 7 preamplifier!


My Adventure with My Old Marantz Model 7k

Part 5: My Way of Modification – Upgrading the Coupling Capacitors

Dedicated to Saul B Marantz and Sidney Smith for their true masterpiece!


Shirokazu Yazaki

Upgrading of the coupling capacitor: The Red, Blue, and Green Cactus Capacitors, True Fame of Made In USA

(Note: In Part 4 Yazaki-san mentioned briefly how he worked closely with Arizona Capacitors, Inc., in Tucson, Arizona, to develop the Red, Blue, Green Cactus capacitors over the last seven years, to achieve specific tonal characteristics that he has been searching for for many years. Now in Part 5 Yazaki-san is telling us about the rest of that Arizona Capacitors story as well as some other very intriguing ideas. - Jeff)

Simply stated, I have felt the sound and the tone of the Red, Blue and Green Cactus hermetic sealed oil-filled capacitors by Arizona Capacitors, Inc., to be so desirable, and I have loved them for their tone that is full of warmth, depth, and sweetness.

The unique very rich and organic mid-low range of these capacitors brings out the healing and the comfort of my favorite music.

I would like to dedicate this chapter to Mr. Daryl Stahler (former general manager) and Ms. Cindy Hilton (Inside Sales & Office Manager) of Arizona Capacitors, Inc., for their help and support in realizing my dreams with the Red, Blue and Green Cactus hermetic seal oil-filled capacitors.

Encounter with Arizona Capacitors, Inc.

I would like to describe my lucky encounter with Arizona Capacitors, Inc., in early June of 2010.

I had just started to study how to bring out the full potential of Honda-san's (now at Infineon Technologies) reference Class-D amplifier design, in early 2007, as I have mentioned before.

At this early stage, I had reached the conclusion that the quality of the capacitors for the low-pass filter had major effects on the final sound quality of the Class-D amplifier.

The low-pass filter is made of a pair of one inductor and one capacitor, and it works effectively in providing the analog signal current for driving the loudspeaker at the final stage of the Class-D amplifier.

It needs a particular specified inductor and a signal use capacitor, 0.47μF, and so it would be just like low-pass filter of speaker network, with the only difference being the crossover frequency is around 400 kHz.

I suppose you could imagine the importance of the capacitor used in the low-pass filter for getting the most desirable sound.

Thanks to the passion of the forerunner of tube amplifier enthusiasts in Japan, I was able to get easily a lot of types and brands of NOS vintage hermetic seal capacitors, like Sprague Vitamin Q, also Sprague HYREL, Dearbone, Aerovox, West Cap, and others, like the NOS Black Beauty and Black Cat, because of their favor in the consumer market.

Searching for nice sounding capacitors has been very interesting work for me, and I found out about the enormous sound potential of NOS hermetic seal oil-filled capacitors that were made for defense use in the USA.

By the end of 2009, I had reached the conclusion that my favorite capacitor for use in this filter was a vintage oil-filled capacitors by West-Cap, 0.47/600, that made for the US military in 1967.

As a coupling capacitor it also remarkably improved the sound of my old WE310A driven DA30 non-feedback SET, with its sound gaining in musicality and with a fascinating and beautiful mid-low range. It’s a NOS vintage capacitor, but it did not have too much heavy bass or old fashioned tone like the famous Sprague Vitamin Q.

Well, Banno-san (my fellow engineer, who is not only a skillful  engineer of analog and digital circuitry even now, but also he plays the piano very much, and has been playing the cello now for more than five years) and I, decided we had to find a currently produced capacitor just like the West-Cap for our Class-D amplifier, when we started Spec Corporation.

Thankfully, I was blessed to come across Arizona Capacitors, Inc., at that time, and succeeded in contacting them, the day after founding our new Spec Corporation company on January 7th of 2010.

Arizona Capacitors, Inc., had just updated their home page at that time, and so I found them by an internet search.

I knew that Arizona Capacitors, Inc., who took over from West-Cap their huge production facilities and their endless engineering drawings, maintained the glory of West-Cap in Tucson, Arizona, with only a change to the company name.  How lucky we were to find them, don’t you think?

Type C 85805, Red Cactus

At first we ordered a custom capacitor made of only Kraft paper and aluminum foil that was our prototype of the Red Cactus. Yes, the Red Cactus is a genuine paper in oil (PIO) hermetic sealed capacitor.

On March 15th of 2010 we received the first samples from Arizona Capacitors. With these samples, we were able select several oils to try for impregnation, to hear which best fit the sound we desired.

The first Red Cactus’ tone was very impressive for us, and the mid-high range was simply fascinatingly beautiful, so pure, and sophisticated.

The tone might fit best for chamber music, especially for violin and female vocals, I believe. That's why I called it Red Cactus, as the attractive tone reminded me of a certain beautiful Hollywood movie star from the old days.

Even now, we use this Red Cactus as the main capacitor in our top of the line amplifier, the RSA-F33EX, and the Red Cactus is Banno-san’s personal choice for its pure tone.

Type C50309, Blue Cactus

The type C50309, which I called the Blue Cactus, was developed to compensate for some of the weakness in the low range of the Red Cactus.

The dielectric materials of the Blue Cactus are made of the combination of Kraft paper and Mylar film. Accordingly the construction of the Blue Cactus was just the same as the vintage NOS West-Cap, which I so loved.

The greatest virtue of the Blue Cactus is its recreation of the rich and powerful sound of the vintage hermetic seal capacitors made in USA, and so the sound has a gorgeous and strong mid-low range.

Of course, the sound of this Blue Cactus surpassed the vintage West-Cap with the transmitted signal information, especially in the mid-high range. In other words, we could say the dynamic S/N ratio and frequency range, were much improved to our hearing, I felt.

We released the Blue Cactus in seven values from 0.01~0.47μF /600 VDC in our domestic market for the enthusiastic tube audio fans in Japan early in the summer of 2011.

We have also mainly used Blue Cactus capacitors in ourRSA-M3EX amplifier, and I suppose the rich timbre and the massive sound of M3EX owes much to the Blue Cactus capacitor.

I named the Blue Cactus capacitor after the vast clear blue skies of Tucson, Arizona, that I experienced at the Pima Air & Space museum, when I visited on October 3rd in 2015.

Type C50313, Green Cactus

The type C50313, Green Cactus capacitor, was released in the summer of 2014, as our latest Arizona Capacitor.

I wanted to achieve a brand-new sound for a hermetic seal capacitor, and Daryl-san’s (the former general manager of Arizona Capacitors, Inc.) idea was to increase the thickness ratio of Kraft paper to Mylar film.

Our goal was that the tonal character, from mid to high end, would be close to the sound of the Red Cactus capacitor, a genuine paper in oil (PIO) capacitor, but with the added benefit of a mid-low range that would be like the Blue Cactus capacitor.

It turned out the sound of the Green Cactus capacitor was nothing like a vintage capacitor’s sound, and the Green Cactus capacitor has a clarity through its entire exceptionally wide range.

I feel somewhat like the Green Cactus capacitor has the sound of the best polypropylene film capacitor, but is still very organic and natural sounding, which is something polypropylene film could never achieve at that level.

And so I believe, this Green Cactus capacitor could easily fit in well for a high-resolution music source in the present day.

We have not yet brought out the latent potential of Green Cactus in our amplifier, but you could already hear and experience the sound of the Green Cactus capacitor with our Real-Sound Processor, RSP-901EX.

When I named the Green Cactus, I was thinking of the majestic scenery of Yosemite National Park in California, filled with granite cliffs, waterfalls, clear streams, and its beautiful giant green sequoia groves.

Cactus marking and Outside Foil

I would like you to know the true meaning of Cactus marking, printed on the Red, Blue and Green Cactus capacitors.

This Cactus marking is the old logo of Arizona Capacitors, Inc., and the marking side shows the outer foil of the capacitor.

The outer circumference of a tubular capacitor’s body must inevitably be one side of its electrode, and this is called the outer foil.

The outside foil is connected to one lead wire of the capacitor, and of course the inner side foil is connect to the other lead wire.

Sometimes inductive noise can be induced on the outside foil by some kind of external electrical condition, but when the lead of outside foil is connected to ground, the inductive noise flows into the ground.

I suppose you have seen the white or yellow lines printed on vintage capacitors like the Black Beauty or Black Cat, and these lines point out the end of outside foil.

At present, almost all capacitors don’t have such and indicator for the outside foil that should be connected to ground. While there is not any polar character in such a signal circuit use capacitor, the directional character from inner foil to the outer foil surely exists in the tubular type capacitor.

Usually, we install these capacitors into L/R circuits for stereophonic use, and it is very important to align the direction of the capacitor for L/R.

People with very sensitive hearing can hear the phase fluctuation if the capacitor is not aligned correctly in both channels, which leads to a wobble or blurring of the sound image.

If you had an oscilloscope or a noise meter, you can easily check the direction, so I would like to recommend that you at first to check the capacitor before you solder it in, and make sure to align the direction for L/R channel.

Also, it is better to install the lead wire of the outside foil into the lower voltage side, or closer to ground. When you use Red, Blue and Green Cactus, Arizona Capacitors, let me remind you that each Cactus marking points out the end of outside foil, and these capacitors have been produced and managed under the quality control of Arizona Capacitors, Inc. to be labeled in such a way.

Physicality of Raw material and Tone Characteristic of Capacitor

I remember well, when Banno-san said to me in early January 2010, after his hearing comparison test of a lot of types of capacitors, including the latest high quality polypropylene capacitors, that “It is just like I heard the sound of the mechanical vibration, or some kind of resonance, of the raw materials of each type of dielectric or electrode itself.”

Banno-san could very clearly hear how the capacitor’s raw materials have much affect on the mechanical and sound character of each capacitor, I think.

Well, the capacitor for signal use works like this: The signal voltage is superimposed on the DC that flows into one side of the capacitor's electrode, and the capacitor blocks the DC so that only the signal current is at the other side of electrode.

In this filtering process, the fluctuation of the electric charge produces mechanical vibration on the dielectric and the electrode. This kind of vibration leads to a modulation of the signal as it flows through the capacitor, I understand.

For this reason, the raw material of the dielectric and electrode will be be very influential for the tone characteristic of the capacitor.

I fully agree what Daryl-san once said to me, that “Capacitors manufactured with exclusively film, such as polyester, polypropylene, Teflon, are described as fast responding, often associated with harsh tonal quality. Additionally, these (typically) dry units also exhibit sonic resonant tendencies that can also yield unwanted effects on the sound quality. Oil filled or impregnated capacitors tend to dampen this effect, giving superior tonal qualities. In addition, by combining various ratios of Kraft paper and film, the tonal qualities can be manipulated to a desired effect.”

In the sound of the Red, Blue, and Green Cactus capacitors, I recognize the common desirable and comfortable tone character in these capacitors, which partly comes from the from the character of the Kraft paper.

I suppose you know very well that high quality Kraft paper is made of genuine pulp, and the main raw material of the pulp is from a conifer tree.

When I think about the conifer, I recall the memory of visiting Muir Woods National Monument near San Francisco, and Yosemite National Park, and having the chance to see the woods of these gigantic conifers.

When I think of such a conifer, I’m also reminded of the simply natural and comfortable low range of my Altec 414A, which I have loved so long a time. The fabric the woofer was made of is the highest quality pulp from conifers with a long fiber length.

I regard Kraft paper as exactly the same sort of natural material, and so it comes as no surprise that the tone of the Kraft paper is organic enough that it warms my heart.

Summing up the fascinating tone of the Red, Blue and Green Cactus, Arizona Capacitors, it must be in part due to the blessing of the great forest resources in North America.

On the contrary, the film, Mylar, polypropylene, Teflon, and the like, has the nature of an elastic body. An elastic body of some thickness, width, and length, inevitably has a characteristic vibration or sonic resonance frequency according its Young's modulus under the condition of some tensile force.

You can easily imagine the same phenomenon with the string of a guitar.

At present, undoubtedly metalized polypropylene capacitors are the mainstream capacitor for signal use in speaker networks.

I fully agree that metalized polypropylene capacitors have a modern and very neat tone, with fine details and resolution, and I know very well that this sort of sound might be accepted and highly appreciated by a lot of music lovers around the world.

But I have felt the tone of metalized polypropylene capacitors don’t have the natural warmth of human touch, and lacks the true naturalness of the hermetic seal oil-filled capacitor that is made of mainly Kraft paper as the dielectric.

I suppose it might come from the fact that the frequency also has a level of characteristic vibration, and with polypropylene it would be higher because of the high Young's modulus (hardness) and the small value of internal loss. I think the metalized electrode might emphasize the tendency.

Woods National Monument

About the foil of an electrode, Banno-san and I, had experienced the tone of aluminum, tin and copper under the condition of the same dielectric material and oil. Tin foil’s tone, we felt was insensitive and cloudy. The tone of copper foil was too rich for timbre for our hearing. We selected aluminum foil because of its natural and organic tone for the Red, Blue and Green Cactus capacitors.

Once again, we found out the importance of balance between hardness and internal loss. Well, I would like to point out again that while our hearing senses can easily recognize these differences in tonality, there is not any measuring method or tools that can describe why this is so.

There is much that is unknown about the world of physical properties and the mysteries of natural materials, and so listening must be one of our truths for analog technology, I understand.

How to use Red, Blue and Green Cactus for the Modifications

I have already recommended to you to use a pair of type C50313-334K, 0.33μF / 600VDC, Green Cactus  capacitors for C049, and three pairs of MZ-103DA, 0.01μF / 500VDC, mica capacitors for C063, C062 and C091.

Now about the four pairs of coupling capacitor that remain, the C065 (0.1μF) and C066 (0.47μF) for the pre-amp (phono EQ), and the C083 (0.22μF) and C092 (0.22μF) for tone amp.

If you selected these capacitors for each part number from the Red, Blue and Green Cactus capacitor choices, there could be 81 varieties of combinations, and so, it seems like it is too hard to come across the best combination because of all the choices.

Above all there must be considerations for your favorite music, your taste in sound, and the nature of your system.

Consider that the Red, Blue, and Green Cactus capacitors each have their own unique and desirable character, but that they share their main dielectric as Kraft Paper, that their electrode is aluminum, and the impregnated oil are exactly the same, so those provide tonal character similarities with each other.

If I could make the analogy about the tone of the Red, Blue, and Green Cactus capacitors, it would be like the taste of single malt whiskies. An excellent single malt would be so nice, but the tasteful blended whiskey could be also worth drinking.

The Red, Blue, and Green Cactus are each outstanding sounding capacitors, but when blended they can bring out another different world of musicality, the one you have searched for.

I strongly believe that you could be the best blender, because you already know well your personal tastes for the sound, and every detail of your systems. So you could find the most favorable musicality through repeating the process of trial and error in such a blending.

Also, please keep in mind that the sound and tone of the Red, Blue, and Green Cactus capacitors will become more desirable as time passes, becoming much more natural, smoother, and sweeter, even six months or a year later.

I would like to tell you that these capacitors have a sufficient amount of transmitted information, so after installing the capacitors, please wait patiently for their full tonal development, and you will surely be rewarded with fruitful results after a long time aging, I swear.

Wet tantalum Capacitor as the best Cathode Bypass Capacitor

I have heard that the wet tantalum capacitor was developed at NASA's request, and it is well known for its high reliability. Some enthusiasts with long experience with tube amplifiers say that wet tantalum capacitors far surpass any electrolytic capacitors.

Surely, early on the wet tantalum capacitor was so expensive that it wasn't easy to use in a usual audio amplifier, but fortunately I have found that NOS wet tantalum capacitors have now become very affordable.

At first, I tried and installed the wet tantalum capacitor as the bypass capacitor at the cathode of WE310A, the driver tube, in my DA30 SET.

The results with the wet tantalum capacitor brought me a breathtaking surprise, as I could now easily and clearly distinguish the sound differences between WE310A mesh sealed and WE310A small punch.

The sound of WE310A mesh was so natural and full of fine details, and I felt the sound was so attractive that I did not want to substitute anything else.

With this modification with the wet tantalum capacitor, the sound image was clear and stereophonic, and I felt a very transparent sound stage spreading from the front to back, and to the left and right. Also, the timbre was so rich and beautiful, like I had never heard before.

I was so encouraged by this experience that I changed the electrolytic capacitors for the vacuum tubes' cathode of the first stage (C062), and the second stage (C064), in the phono EQ of my old Model 7k to wet tantalum capacitors, and I got same types of improvements.

Of course, I made same modification to Ookubo-san’s Model 7 Replica, which was released in Japan in the middle of the 1990’s, and to Handoko-san’s original Model 7, both with successful results.

So I will strongly recommend to you to change to wet tantalum capacitors in these positions for bringing out the full potential of the famous Marantz 7’s phono EQ. Surely, the wet tantalum capacitor is a unique one, and does not require any help from a mica capacitor connected in parallel.

Thank you for reading about my life-long quest for “Real-Sound”, I have experienced many wonders along the way.

To be continued.


A big thank you to Yazaki-san for his fascinating discussion about capacitors, and sharing with us the modifications he has made to his vintage Marantz Model 7k preamplifier, it is both intriguing and enlightening!

As always, thanks for stopping by, and may the tone be with you!

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