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Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25A (DA30) Monaural SETs - Part 5!

10-26-2022 | By Jeff Day |

It's always a pleasure to hear from friend Yazaki-san about his latest adventures in Real Sound, and in Part 5 Yazaki-san tells us about his latest discoveries with the GEC PX25A monaural amplifiers he built for his friend Alan-san to use with his vintage Altec Corona loudspeakers.

I always learn a lot from Yazaki-san's articles, and really enjoy reading them. I would like you to join me in saying "Thank you!" to Yazaki-san for taking time to write these articles, and for sharing his audio adventures and insights with all of us.

Without further ado, here's Yazaki-san's latest article for your reading enjoyment!

Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25A (DA30) Monaural SETs - Part 5!

I spent a very fulfilling two and a half days, from the 2nd of October to the 5th, visiting with my close friend, Alan-san and his wife Paula-san, at their house. It was as if my half-century of audio life and adventures were condensed into one moment during our time together, and we were really able to have some wonderful experiences, fully enjoying music and sound. It was truly a moment of grace for me, and a true delight to my soul!

Yes, this story is a report on the latest modifications to Alan-san's two sets of WE310A driven PX25A (DA30) mono SETs, both the Hashimoto transformer version and the old Tango transformer version. 

So this article would effectively be Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25A (DA30) Monaural SETs - Part 5!, but if you want a better understanding of the context for this report, I’d like you to refer to my previous articles, Part 1 (HERE), Part 2 (HERE), Part 3 (HERE), and Part 4 (HERE). 

Alan-san's Altec Corona Loudspeakers

The JBL2405 Add-on Super Tweeter System

At last, I was able to see the vintage Altec Corona loudspeakers for the first time,  and found Alan-san’s Coronas to be in mint condition, even though far more than half a century had passed since they were manufactured. 

In particular, each of the two Corona's back boards, which have a large surface area, were made of American pine or Douglas fir plywood, which is rare to get nowadays. They are ideally dried now, and when struck with my knuckles they produced a pleasing sound. This is a phenomenon that can never be seen or heard in modern speaker boxes made of MDF and the like. 

Furthermore, the exterior design can only be described as beautiful, as it naturally blends into a wonderfully tasteful and spacious room. 

Well, to tell the truth, one of the purposes of this visit was to confirm with my own ears how the JBL 2405 add on super tweeter system, that I built up 4 years ago now, actually works on Alan-san’s Altec Coronas with his two sets of mono SETs. 

The reason I proposed this super tweeter system to Alan-san has already been detailed in My Adventure with My Old Marantz Model 7, Part 10 (HERE).

I hope it might be helpful especially for those who love the vintage Altec large-scale 2-way horn speakers. 

Here are the main points from Part 10: 

As I've described, I'm a self-confessed follower of Altec vintage loudspeakers, and I have been actually a long-time user, but when compared to the modern designed wide-range speakers, I felt a shortage in the highest frequency range, which is also close to the audible limit of this 2-way loudspeaker system. 

I’m sorry, but I have to conclude that there was a fatal strategic error in the Altec product development plan of that time. I think the long-term success of the 604 series as studio monitors during the 1950s and 1960s may have cast a shadow over it on the contrary. 

In studio monitors, and in the general consumer market, Altec had fallen behind JBL from the end of 1960s and early 1970s, probably because a good quality and full-fledged tweeter had not yet been developed by Altec. This lagging behind occurred at the same time of the widening frequency response of recordings and the improved high-fidelity of electronics.

First of all, the design and the structure of Corona's box is superb. There is only one parallel plane, top and bottom, and it would reduce the harmful effect of inner standing waves, and the slim legs could bring out highly the resolution of the low range, I suppose. 

The woofer of vintage Altec 803A, 416A, and 414A, would be the best one for reproducing very natural and beautiful mid to low range frequencies among an awful lot of types of woofers in all ages and countries, I believe. 

Well, I have regarded two-way loudspeaker systems as the ideal balance between the range and the coherent characteristic of the total sound. We could feel the good coherent or phase characteristic as the feeling of comfort while listening.

Multi-way systems of more than two drivers could not easily bring out such a comfortable feeling, as you might have already experienced.

About the Altec system, the sufficient range and its good phase characteristics would be realized by the outstanding woofer and horn system, a two-way with a simple crossover network. 

The one negative point would be the rapid roll-off from 10 KHz of the compression driver. I believe the range of over 10 kHz would be rather important for getting the airy soundstage and the definite outline of the sound images. Especially now, as such signal information is much more accentuated in present music sources, so it was fortunate that the roll-off curve over 10 KHz was so smooth, and so the addition of a super tweeter with a simple high-pass filter could be successful, I think.

The Sound of Altec Corona Loudspeakers with the Addition of the Add-on JBL2405 Super-Tweeters  

I felt the JBL2405 add-on super-tweeter was in perfect harmony with the Altec Corona loudspeakers without adding any discomfort. 

The excellent tone was probably due to Alan-san’s exquisite level setting of JBL2405, which had a very organic and natural warmth to it. 

The JBL2405 is a wonderful tweeter. In other words, we were not aware of the existence of the tweeter at all. With the addition of the JBL 2405, the spatial presentation filled a large wall, and furthermore the very subtle nuances of female vocals, for example, sounded elegant and attractive. 

The horizontal directivity of JBL2405 is remarkably good among horn tweeters, with vast spaciousness, which was an excellent match for Alan-san’s large living room. Anyways, this was exactly what I was aiming for, and my initial hypothesis or assumption was confirmed during our listening. 

The Corona loudspeakers by themselves, without the JBL2405 super-tweeters, I couldn’t help but feel that the sound was a little bit old-fashioned and lacked clearness and openness. 

In conclusion, I’d like to recommend adding the JBL2405 super-tweeters system to Altec loudspeakers to all you Altec lovers as a radical and contemporary improvement in the sound quality of vintage Altec 2-way loudspeakers.

Alan-san’s Impressions of the Altec Corona Loudspeakers with the JBL2405 Add-on Super-Tweeter System!

“Earlier this October my wife and myself were blessed with a visit from Yazaki-san, a kindred spirit that is a very gentle and generous soul. My introduction to Yazaki-san was through Jeff-san’s blog and we have developed a wonderful relationship. Luckily, Yazaki-san has openly encouraged me to share in his audio path of his Real Sound Adventures. Most importantly, I am eternally grateful to have Yazaki-san as my close and dearest of friends.”

“Yazaki-san encouraged me to purchase this pair of vintage Altec Corona loudspeakers to mate with his continuously improving Marantz Model 7 preamplifier, and the Western Electric 310A and DA30 monaural SET amplifiers (with versions having both the Hashimoto and Tango transformers).”

“These were all linked together with the lovely NOS Western Electric WE16GA wiring.“

“The speakers are absolutely excellent transducers; however, there is a roll-off of the reproduced sound around 10KHz with these Altec Corona loudspeakers. Nevertheless, the in-the-moment reproduction of the Altec Corona loudspeakers provided a palpable realism that was immediately and happily addictive for us!”

“Later on, I received an email from Yazaki-san asking me if I would like to try an add-on JBL2405 super-tweeters which would provide extended frequency response for the vintage Altec Corona loudspeakers. I happily agreed, and off we went on this new adventure.” 

“As described by Yazaki-san in this article, the JBL2405 super-tweeter system comes with a flexible adjustable crossover system that he designed for this application.” 

“I must say, the integration with my Altec Corona loudspeakers is seamless and transformative in nature. There was an awakening of these lovely Altec Corona loudspeakers, complementing the original design, that gave a welcoming lift to the music, and surprisingly, brought forth a much more real, detailed, deep and wide 3D soundstage. I could feel the placement and outlines of the different instruments and voices, dancing along with a tactile in-the-room style of presentation of the musicians.”   

“Early in October, when Yazaki-san first heard my Altec Corona loudspeakers with the add-on JBL 2405 super-tweeter system, he expressed the same impression that I experienced upon first hearing the add-on JBL 2405s, which simply fits hand-in-glove with these speakers. Thank you, Yazaki-san for recommending the add-on JBL  2405 super-tweeter system!" 

The iPhone Adventure with Alan-san

It was Alan-san himself who named our marvelous experience the “iPhone Adventure”. We were really intoxicated by the wonderful and enjoyable music of the YouTube videos playing from his iPhone 12 during our final session in the afternoon on 4th October. 

At first, I prepared and hand-carried from Japan only two items, my Android Oppo Reno A cell phone, and a very small USB DAC, so I could check the sound quality of the modifications for the version upgrade of Alan-san’s mono SETs. 

These are neither a high-fidelity high-resolution source, nor high-quality high-resolution digital devices, and therefore, the prices of each were incredibly reasonable and affordable to purchase. 

Normally, these devices are not suitable for hearing tests with high-end audio equipment, and to review their performance. The small USB DAC is a “Douk Audio U4, Mini Bluetooth5.0, Valve Tube, Headphone Amplifier DAC and Stereo Preamp USB Sound Card”. 

For the past year or so, when I go to bed, I usually listen to my favorite music on YouTube videos, through the earphones attached to my mobile phone, and fall asleep while listening to this wonderful music. 

Of course, the sound quality of the music might be even better with high quality audiophile headphones, but I’m more than happy enough with my earphones for this use. 

There are probably two reasons for this. Of course, the first is that the sound quality of headphone output has become extremely good recently due to developments in digital technology. Also, the compressed audio format called MP3, which supports the sound of YouTube videos, turns out to be an excellent format for transferring music in a very natural and familiar way for human hearing. 

Let me be a little bold, am I the only one who feels that the MP3 format can be more musical than the CD format? 

On the other hand, even for recording for YouTube audio, the fact that it has become easy to obtain a really simple PCM recorder with excellent performance has contributed to the excellence of recent YouTube music quality. 

Well, as for this system, I suppose, with the headphone output of a YouTube video, which has already been converted to an analog signal in the mobile phone, might be transmitted by Bluetooth from the mobile phone to the USB DAC, and probably without any digital processing it might be received by the RCA 5670 tube, working as a buffer, with the signal output being low-impedance.

So the better the sound quality of the headphone output, the higher the purity of the output of the USB DAC could be brought, and this very simple signal path makes the freshness of the sound quality possible.  

Well, the purity and freshness of this USB DAC output seemed to be of a very high quality, although it definitely deteriorated through the tone amplifier of the Marantz Model 7. 

Please consider that Alan-san’s Model 7 is not only in the excellent condition, but also that I have already made performance upgrades to it twice.

I realized once again that the simplification of the signal path is an extremely effective and universal concept for my long seeking of “Real Sound”.

So, the reason why I adopted this audition source during my visit was that it was a sound source with high reproducibility. And, as Alan-san pointed out, it was just about being able to play our favorite high-quality YouTube videos “On Demand” at any time. Also, it allowed us to even adjust the volume level with our mobile phones. 

Anyways, in a limited two and a half days, with the evaluation of two sets of SETs monaural amplifiers after the version upgrade, doing hearing comparisons between non-feedback and newly improved PK feedback, for determining the sound quality differences between STC4328A and WE328A vacuum tubes, etc., a lot of hearing sessions were planned. Therefore, it was almost impossible to do the auditions using Alan-san’s favorite analog LPs, which required many preliminary rituals. 

In addition, I replaced the vacuum tube of this USB DAC with a vintage compatible tube, the RCA 5670. It is my favorite tube because of its bright and gorgeous sound, which was common to RCA miniature tubes of the 1950’s and early 1960’s. Fortunately, the WE 396A is also a compatible tube, and Alan-san and I are looking forward to listening to the sound and the tone differences between RCA 5670 and WE 396A. Of course, it would be fun time for each of us.

Furthermore, the last session was an amazing shock for me. Until then, the mobile phone I used to send out sound sources was my Android Oppo Reno A, and the sound quality was also worth listening to. 

However, when we changed to Alan-san’s iPhone 12, we recognized at once the sound and vocals changed completely. The frequency-range and dynamic-range of the sound expanded overwhelmingly. The physical characteristics were clearly changed and improved.

Anyways, I would like to hear Alan-san’s thoughts on the enjoyment of listening to YouTube videos using his iPhone 12. For me, my time was limited, so only a few songs could be heard of the sound of iPhone 12 at that time.

Two weeks have passed since my visit, and the sound quality of the modified 2 pairs of mono SETs must be even more natural and smooth by now. Therefore, Alan-san’s impressions will provide additional useful information for the eager and enthusiastic readers of Jeff’s Place, I believe.

Alan-san’s Impressions of Using the iPhone 12 and Douk Audio U4 Mini USB DAC as a Source

“Yazaki-san’s visit with us included major revisions to both models of the the WE310A and DA30 amplifiers. Recently, Yazaki-san was able to make two new changes to the amplifier’s circuits, and thought it would be best to make the changes here, instead of me shipping the four amplifiers back to Japan.” 

“Also, it would give me a chance to listen to the two options and make a decision regarding which one I preferred for both amplifiers. First, with the non-feedback option, and then with the new PK feedback option. However, most importantly, Paula-san and I would be able to have a wonderful time of fellowship and visiting with our dear friend, Yazaki-san.”

“This was a major undertaking to make all the required changes. Hours and  hours of building up the no-feedback option, listening, and then going through the process of building up the PK feedback option. First, both changes for the Tango transformers version of the monaural SET amplifiers, and then following up with the changes for the Hashimoto transformers version of the monaural SET amplifiers.” 

“This brings us to the iPhone 12 Adventure! It was important for us, after making the changes, to listen to the same music selections while making choices for the no-feedback and PK-feedback solutions.” 

“Yazaki-san brought his mini USB DAC, the Douk Audio U4 with a stellar RCA 5670 tube to bring out the magic of the mini USB DAC. For simplicity, we drove the amplifiers directly with the Douk Audio U4 mini USB DAC.   The first thing I thought was, “Really, this is not possible, it sounds amazing, not with the server and source we are utilizing!” Yazaki-san had a little smile on his face and said, “Amazing, huh?””   

“We spent hours and hours of blissful listening, and we laughed a lot! I gave credit to the wonderful genius of the RCA 5670 vacuum tube, and Yazaki-san shared the credit with my iPhone 12, and the wonders of YouTube providing the source material. This was really an unexpected surprise, and the Douk Audio U4 mini USB DAC was really an amazing piece of kit with the RCA 5670 tube. However, this will be followed by a new tube adventure with a NOS Western Electric 396A tube in the future.”

“Anyway, just before Yazaki-san left to return home, I became very lucky. He presented me with this wonderful Douk Audio U4 mini USB DAC, as a gift to memorialize our memorable adventures in real sound and our precious time together!”

The Second Installment of Part 5 Will Be Coming Soon!

I wrote this article, the first installment of Part 5, because I wanted to introduce Jeff’s Place readers to how we evaluated and enjoyed the results of the two sets of Alan-san's mono SET amplifiers upgrades. 

In the upcoming second installment of Part 5, I’d like to introduce the details of the modifications for the version upgrades.

Yes, I will talk about sound quality improvement measures that can be applied to almost any tube amplifiers, commercial or DIY, single-ended amplifiers or push-pull amplifiers.

Also, I want to talk about the hearing comparison between completely non-feedback and newly improved PK feedback, which is possible only for tube amplifiers with excellent basic characteristics.

Additionally, I’d like to report to Jeff’s Place readers about the sound differences between the rare vintage 7.5V specification driver tubes, the STC 4328A mesh and the WE328A mesh.

Anyways, I hope the first installment of Part 5 will be some kind of help for you, and if you look forward to second installment of Part 5, my motivation will be greatly stimulated!

Thank you very much for reading this far, so appreciated! 

Well, Yazaki-san's article was full of surprises!

Being a vintage Altec loudspeaker nut myself, I was particularly intrigued by the add-on JBL2405 super-tweeters to Alan-san's Altec Corona loudspeakers, which addresses the most common complaint about vintage Altec loudspeakers of being a little soft on top. 

I have been hearing from quite a few listeners now about using the iPhone as a source in combination with a USB DAC. Apparently, this approach has become the default for many young listeners, so I was quite intrigued by Yazaki-san's and Alan-san's listening impressions with the iPhone 12. Expect to hear more on this topic of using an iPhone for a source in the future. 

Yazaki-san, I am very much looking forward to your second installment of Part 5 about the modifications to Alan-san's monaural SET amplifiers!

As Yazaki-san mentioned in his article, you can catch up by reading the previous installments of this developing story at the following links:

October 2018: Adventures in Real Sound with Yazaki-san: Alan-san's GEC PX25 monaural SETs! (HERE)

November 2018: Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25 monaural SETs - Part 2! (HERE)

January 2019: Adventures in Real Sound with Yazaki-san: Alan-san’s & Harald-san's GEC PX25 monaural SETs - Part 3! (HERE

May 2019: Adventures in Real Sound with Yazaki-san: Alan-san’s GEC PX25A (DA30) Monaural SETs - Part 4! (HERE

For those of you who desire to read more about Yazaki-san's adventures and insights into Real Sound, you can find a wealth of information in the Archives section of Jeff's Place.

Click on the Archives link (or HERE), and scroll down to where you see Adventures In 'Real Sound' with Mr. Shirokazu Yazaki.

At the current count there are links to 55 articles for your reading enjoyment!

Many thanks to Yazaki-san for taking time to write his articles, and for sharing his insights and wisdom with us about Real Sound. Thank you Yazaki-san!

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

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