The JLH Gateway to Class-A - A Golden Jubilee Tribute


Gateway to Class-A -- Building the JLH Classic-1969


John Linsley-Hood (1925 -- 2004)
Audio designer nonpareil

John Linsley-Hood -- Truly a legendary name in audio electronics, whose signature Class-A amplifier design has achieved cult status and the 'classic' moniker in our times. More than half a century after publication (in Wireless World, April 1969), his "Simple Class-A 10 W amplifier"  is considered unmatched in simplicity and subjective audio quality. In this series of posts my attempt is to preserve for enthusiasts and DIYers the work of this great man, and perhaps offer a gateway, a "single window", into the audio world of 'JLH' (as he is fondly known worldwide), with the stress on the Classic-1969 design. The material presented here from authentic archives and other sources in my decades-old collection, is sure to keep enthusiasts occupied for many summers and winters, reading, building, and enjoying the fruits of the build in the manner the Master himself indicated. JLH had simply put it this way: " My main interest was in music, not in circuitry, so I thought it would be prudent to ask my ears what they thought ..." The great man was a first-rate engineer and designer, and his genius shines through in his timeless designs. But his greatness truly lies in how he was able to strike a fine balance between the science and art of audio design.

Epitaph for Sir Isaac Newton

        It is likely that most have heard of the poet Alexander Pope's famous epitaph for Sir Isaac Newton. It is a quote that I recall every time I think of my all-time 'hero' and 'Manasa Guru', John Linsley Hood. (The famous Sathya Sai Baba Bhajan goes: "Manasa Bhajare Guru Charanam...", which translates to "O mind, meditate at the feet of the Guru...".)  I'm virtually certain that Gabriel (the angel tasked with record keeping in Heaven) has in his files an equally pithy saying by God about our beloved John Linsley Hood too. Most of those who knew him and/or his work would love to remember him the way he is summed up in the words of an ardent fan and DIYer: " ...his work has made a lasting impact in the world of DIY electronics ... we should also celebrate his life that produced so much educational material and well-loved electronic designs which were often freely published for all to use, helping to create a whole new generation of electronic DIYer's..."

Gabriel, the 'Recording Angel'

        Another adds: "JLH was one of the most highly respected electronic engineers in the world, and his influence on the design of quality audio amplifers has been considerable ... the man himself may have passed away, but his great work will live on and will inspire future generations of engineers. His designs have brought pleasure and musical enjoyment to DIY'ers and lovers of music . Hope you're up there reading this Mr. Hood, and I trust God has set aside his premium workshop for you with lots of attractive angel assistants, and I'm sure heaven will sound a lot better with a JLH Class-A rig!"

The Magic of the JLH 'Classic-1969'

        Such sincere adulation and accolades are not commonly found in the annals of audio engineering. 'Diyaudio', the rightly famous do-it-yourselfer's online forum, has had many discussion threads running right from the publication of JLH's "Simple Class-A 10 Watt Amplifier" in the UK magazine Wireless World in April, 1969. And, guess what, the thread started in 2002 is still going strong today with the number of posts nearing 10,000! His timeless work has indeed continued to inspire generations of engineers and hobbyists. That his design has endured through the past half century marked by epochal technical developments, and is still delivering performance that offers a challenge to the 'best" designs of today, is the greatest testament to the genius of JLH.

        As I look back today, I see myself as a college age young hobbyist who was fortunate to build his '1969' design in the late 1970s, but who in utter folly chose to chase instead the other higher power amp designs of the period, ultimately reaping no lasting satisfaction from the mad quest. Like good wine that matures with age, it needed the passage of a few decades for the young man in me to mature 'audio-wise', and once again resolve to set out to build 'the original' and enjoy the magic of the spell cast by the JLH class-A amplifier.

Coming Full Circle in the 21st Century

        Is there another classic design that has stood the test of time as  the JLH Classic has over the past half century and more? Unlikely. Enthusiastic designers and DIY 'modders' have over the decades tried out umpteen mods and tweaks of the JLH, each of them satisfying the designer/tweaker and his close followers. Even the great Nelson Pass paid his tributes with his PLH amp design. Another well-received paen to JLH is the DLH amp by Diego M J, presented in Diyaudio.

        But DIYers the world over are indebted primarily to Geoff Moss who meticulously hosted all available JLH material in The Class-A Amplifier Site (TCAAS), and also made his own contributions to sterling builds of JLH amps. As the 'go-to wiz' for all things JLH, he was a constant presence in the forums even when age and health issues troubled him. Another notable designer in this context was the late Graham Maynard whose work also added to the JLH cache of audio wisdom. Of course, JLH himself had in 1969 and later in 2005 come up with more 'modern' implementations of his timeless design. But the 'JLH-1969' perhaps holds the record for making most of the builders come full circle, back to the classic design. Yours truly included, and therein lies the timeless magic of JLH!

The Roadmap

        These posts are meant to share with my readers and fellow DIYers my Golden Jubilee Tribute to the great Master JLH -- a 2024 build of the Classic design. Naturally this build reflects the insights I have garnered over the decades, and includes minor tweaks which I have found to be fruitful, but which in no way poses a threat to the 'sound' of the Master's design. At this point in time when my aging ears have made me sceptical of reposing any trust in them fully anymore, I recall with gratitude the many hours the "younger ears" in my group have spent in my company, helping me out with many accurate subjective assessments of the final build. My happiness is redoubled to see that the gen-Z too have fallen under the spell of the JLH Classic despite having grown up in the "high end" megabuck audio atmosphere of today. 

        A humble caveat to the reader is in order here. My attempt here is to offer to the JLH enthusiast a "single window" into the history/roadmap of the JLH corpus on the 1969 Classic amplifier, capping it all with my 2024 build of the JLH Classic amplifier. Virtually all of the published work of JLH related to the 'Simple Class-A Amplifier'  which I have been able to source will be accessible through these pages-- with major thanks going to the Grand Old Man Geoff Moss for his devotion and painstaking work collecting and hosting JLH circuits.

        No doubt, the hobby/discussion forums have been a veritable treasure chest of ideas and inspiration as regards the JLH-1969 amplifier. But over the previous decades, the voluminous accumulation of material (Imagine sifting through 10,000 posts, not to speak of the other hundreds of sources!) have transformed the forums into a churning ocean of riches, but not easily explorable by even the most intrepid of DIYers. My copious brief notes taken over the years could be of some help to the hobbyist here, I guess. The same goes for the collection of various circuit mods and redesigns and builds. By no means it is claimed that they are comprehensive or all-inclusive. But I believe they will serve to offer new ideas and limitless inspiration to the enthusiast trying to 'get a handle' on the JLH Classic-1969 amplifier.

        No tribute to the great man will be complete without reference to the voluminous cache of articles he has left behind. In order to avoid confusion, a new "single window / gateway" to host virtually the entire collection of his published material over the previous decades in various tech journals has been planned. (A few articles have been unavailable, but the majority have been sourced from authentic archives, including my own personal collection.) Selected articles, broadly in chronological order, with introductory commentary, will be carried in each blog post. Do visit the following link, but be reminded that it is a huge undertaking, and a "work in progress"; but rest assured that if it has been published by JLH, it would be available here...eventually!

https://jlh-memorabilia.blogspot.com/2024/12/jlh-memorabilia-past-perfect.html

        Let us without further ado move on to the the JLH collection -- the Classic-1969 first -- in the upcoming posts.

        Do read, comment, share -- and build and listen!!

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